Monosaccharide Transport A

Arch Dis Child: first published as 10.1136/adc.42.224.341 on 1 August 1967. Downloaded from Review Article

Arch. Dis. Childh., 1967, 42, 341. Sugar Malabsorption Due to Deficiencies of Disaccharidase Activities and of Monosaccharide Transport A. HOLZEL From the Department of Child Health, University of Manchester In many societies including our own, carbo- maltase, were secreted by unspecified cells of the hydrates play a major part in the total calorie supply. intestinal mucosa into the lumen of the gut where According to the National Food survey figures the hydrolytic process took place. But studies in (Greaves and Hollingsworth, 1964), the average man during the past decade (Borgstrom, Dahlqvist, daily diet of adults contains nearly 350 g. of this Lundh, and Sjovall, 1957; Dahlqvist and Borgstrom, constituent. Diets of course vary with eating 1961) demonstrated that disaccharidase activity in habits and social class, but the dietary carbohydrates the intestinal lumen was extremely limited and did are largely ingested as poly-, oligo-, and disaccha- not account for the amount of carbohydrate rides. In the very young, however, the carbo- absorbed. They further indicated that the majority hydrate intake may consist almost entirely of of disaccharides were absorbed unhydrolysed and disaccharides, though this phase is now getting split intracellularly, a fact that accorded well with progressively shorter. As the rapid decrease in experimental findings (Cajori, 1933; Fridhandler

breast-feeding has been followed by the early and Quastel, 1955). copyright. introduction of cereals into the cow's milk formulae, The problem of localization of the sugar-splitting even the infant of only a few weeks of age has also enzymes was brought nearer its solution by Miller to digest polysaccharides. and Crane (1961), who were able to separate the The percentage of calories derived from carbo- brush-border from the rest of the intestinal mucosa hydrate increases from 40% in infancy to well over of the hamster, and found that the whole of the 50% later in life. The polysaccharides, starch and enzyme activity of the mucosa was accounted for by glycogen, are hydrolysed by salivary and pancreatic this layer. (-galactosidase (lactase) activity had

amylase to maltose and small quantities of isomal- been localized in the microsomes ofthe rat intestinal http://adc.bmj.com/ tose and glucose. The common disaccharides in mucosa by Doell and Kretchmer (1962), while our food are lactose and sucrose. The amount of Dahlqvist and Brun (1962), employing histochemi- lactose depends on the milk intake, as this is its main cal methods for the recognition of invertase and source. The human intestinal mucosa has there- trehalase in various animal tissues, associated their fore the task of absorbing large quantities of the activity with cytoplasmic granules. As yet there is disaccharides, maltose, isomaltose, sucrose, and no definite information concerning the possible lactose. For a long time surprisingly little attention relationship of the elements of fine structure of the was paid to this important absorptive function of the microvillus with its absorptive and digestive on September 26, 2021 by guest. Protected small intestine, but during recent years physiologists, functions. However, two related fractions have biochemists, and paediatricians have discovered been obtained by density gradient centrifugation of much of interest, and clinical observations have tris-disrupted brush-borders from hamster intesti- revealed a number of disorders associated with nal mucosa, and have been identified as the micro- sugar malabsorption. villus cores and their surrounding membranous coats (Overton, Eichholz, and Crane, 1965; Physiology of Disaccharide Absorption Eichholz and Crane, 1965). Until a few years ago it had been accepted that hydrolysis of the disaccharides into their component Specificity of human intestinal disacchari- monosaccharides had to precede their absorption dases. The belief that each enzyme has its and entry into the further stages of metabolism, and corresponding specific substrate has been modified that the disaccharidases, lactase, sucrase, and in so far as experimental and practical experience 341 Arch Dis Child: first published as 10.1136/adc.42.224.341 on 1 August 1967. Downloaded from

342 A. Holzel has shown that synthetic sugars which have the to slightly different conclusions, and thus to some- same glycosidic linkage as naturally occurring what differing nomenclature. Dahlqvist recognizes products will be split by the same enzyme. four maltases, while Auricchio and colleagues The following human intestinal disaccharidases separate five (Table I). have been identified by heat inactivation experiments (Dahlqvist, 1962; Dahlqvist, Auricchio, TABLE I Semenza, and Prader, 1963), gel-filtration on Classification of Maltases Sephadex and chromatography (Auricchio, Semenza, and Rubino, 1965c; Semenza, Auricchio, and Dahlqvist (1964a) Auricchio et al. (1965c) Enzyme Substrate Enzyme Rubino, 1965a). The maltases or ao-glycosidases Maltase Ia Isomaltose Maltase 5 hydrolyse maltose, isomaltose, sucrose, and palati- (isomaltase palatinase) Palatinose (isomaltase palatinase) Maltose nose. Trehalase exerts its activity on trehalose, a Maltase Ib Sucrose Maltase 3 (sucrase) (sucrase: invertase) Maltose Maltase 4 rare disaccharide that occurs in certain mushrooms. Maltase II Maltose Maltase 2 The 3-glycosidase lactase (P-galactosidase) attacks Maltase III Maltose Maltase I cellobiose, in addition to lactose. Cellobiose is a disaccharide resulting from the digestion of cellulose, which consists of two molecules of Maltase 5 (in the latter classification) hydrolyses glucose with a 1-4 3 linkage similar to that which maltose, isomaltose, and palatinose, a synthetic sugar joins the glucose and galactose molecules in consisting of one molecule glucose and one molecule lactose (Fig. 1). Although cellobiose plays little fructose in 1-6o0 linkage. Since palatinose and isomaltose have the same glycosidic bond, they are , galoctosi dase split by the same disaccharidase (Fig. 2). Palatinose can therefore be used to demonstrate isomaltase * *I * a~~ activity (Auricchio, Prader, Murset, and Witt, 1961) when isomaltose is in short supply (Fig. 2). * 0 *4 * * * 0 0 0

MALTASES copyright. Lactose Cellobiose Invertase Isomaltose FIG. 1.-f-galactosidase hydrolyses two disaccharides of different molecular composition but with the same * *ff<2 S glycosidic linkage. 0 0 * * 4 * 0 0 * 0 0 0 0 part in human nutrition, since cellulose cannot be * 0 0 6 0 6 0 0 hydrolysed in the small intestine, the sugar can be *Sucrose0 somaltose *0Polotinose: Maltose used as an additional substrate to verify lactase FIG. 2.-Isomaltase hydrolyses in addition to isomaltose http://adc.bmj.com/ activity. The presence of two intestinal lactases palatinose, a synthetic disaccharide. was demonstrated by Heilskov (1956) for the calf, and for the rat and rabbit by Doell and Kretchmer Distribution of disaccharidases along the (1962), who found one lactase associated with the small intestine. Comparison of a number of particulate fraction which hydrolyses two substrates, published animal and human investigations reveals namely lactose and ortho-nitrophenyl-3-galactoside, the presence of species differences. In the rat, while the enzyme the latter. lactose is in the middle of the soluble splits only activity stronger part on September 26, 2021 by guest. Protected Since ortho-nitrophenyl-3-galactoside is an artificial small intestine than in its proximal or distal regions, compound, the true function of the second enzyme maltase activity is uniformly distributed, while is unknown. Two lactases have also been postula- sucrase (invertase) and isomaltase are strongest in ted for the human intestinal mucosa (Semenza et al., the proximal areas. In the adult pig, the trehalase, 1965a). These authors have been able to show that lactase, and cellobiase activities are strongest in the the two 3-galactosidases in the mucosa of the proximal part, while the maltases are most active in human jejunum and ileum are not the result of an the distal part (Dahlqvist, 1964a). In adult man, artefact, and that the ratio of cellobiase activity according to Auricchio, Rubino, and Miirset (1965a), remains constant in relation to that of each of the enzyme assays on mucosal specimens obtained by lactases, further indicating that cellobiase and peroral intestinal biopsy indicate that sucrase, lactase activity are due to the same enzyme molecule. isomaltase, and lactase are less active in the first part With regard to the multiplicity of human maltases, than in the remainder of the duodenum; in the Dahlqvist (1964a) and Auricchio et al. (1965c) come upper jejunum and the last segments of the ileum Arch Dis Child: first published as 10.1136/adc.42.224.341 on 1 August 1967. Downloaded from

Sugar Malabsorption 343 disaccharidase activities are of the same order of decreases gradually to its lowest level in the adult magnitude. Taking the rate of absorption as a specimen. In other animals such as mice, rabbits, measure of disaccharidase activity, Gray and and guinea-pigs, the P-galactosidase activity may Ingelfinger (1965) found, with the aid of infusion decrease at different rates in the jejunum and ileum experiments, that sucrose absorption was about (Koldovsky, Heringova, Jirsova, Chytil, and twice as rapid in the human jejunum as in the ileum. Hoskova, 1966) according to the pH. In rats and Ingested sucrose was almost completely absorbed in pigs, sucrase (invertase) activity is not evident at the jejunum. In a study of 7 normal adults, 6 men birth, but develops later. Injections of hydrocorti- and 1 woman, Newcomer and McGill (1966) sone into young rats caused invertase activity in the carried out 6 to 13 peroral mucosal biopsies in each small intestine to appear at an earlier stage than subject at various levels of the small intestine from normal (Doell and Kretchmer, 1964). This was the first part of the duodenum until well into the further supported by immunochemical studies with ileum. Lactase, sucrase, and maltase activities were a fluorescent antibody technique (Doell, Rosen, and determined; disaccharidase activity was low in the Kretchmer, 1965). In man, lactase activity remains duodenum and ileum, while peak activity was found at a high level provided it is not altered by external at variable points in the jejunum and proximal ileum. factors. Foetal and neonatal intestinal disacchari- Sugar Transport dase activity. The prenatal and postnatal develop- Assuming the disaccharide-splitting enzymes to ment of disaccharidase activities is of importance be intracellular, the means by which sugars enter not only for academic reasons, but also in connexion the mucosal cells is still obscure. This could be by with the practical management of the very small diffusion, if for instance rapid hydrolysis of the premature infants. Lactosuria in the premature disaccharide within the cell maintained a gradient baby was recognized and explained half a century between it and the intraluminal medium. For ago by the absence of lactase activity (Langstein and glucose and galactose there also exists an active Meyer, 1914), the enzyme being functional in the carrier system. Actively transported sugars, i.e. full-term infant. An investigation of 32 human those transported against a concentration gradient, copyright. embryos, foetuses, and newborn infants (Auricchio possess certain structural features in common, a et al., 1965a) revealed that the enzyme activities were pyranose ring, an oxygen bridge between Cl and distributed uniformly throughout the small intestine C5, and a free -OH group at C2. except in the duodenum and terminal ileum, where A further essential requisite is the presence of only trehalase remained high. All glycosidases sodium ions on the membrane of the mucosal cell. were present by the third month of intrauterine life. Substitution of lithium, magnesium, or choline for

All a-disaccharidases (namely the maltases and sodium prevents active transport. The driving http://adc.bmj.com/ sucrase) reached a maximum during the sixth or force is regarded as a form of biological pump, with seventh month of intrauterine life while the 3- adenosine triphosphate (ATP) providing the im- glycosidases, lactase and cellobiase, developed more mediate energy source. Ouabain, phlorizin, and slowly before birth and reached their peak at term. 2: 4-dinitrophenol inhibit the absorption of glucose Premature infants had a low level of lactase activity and galactose. It has been suggested that ouabain which, however, rose rapidly in the postnatal period acts by virtue of its property of disturbing tissue independent of milk intake. Dahlqvist and Lind- electrolyte metabolism (Davenport, 1966). berg (1966), who studied human foetuses between Littman and Hammond (1965) have proposed on September 26, 2021 by guest. Protected 11 and 23 weeks of intrauterine life, found invertase that sugars enter the intestinal cell by means of a and isomaltase activities fully developed before the ternary sugar-Na-carrier complex. This carrier 11th week, trehalase between the 11th and 23rd would possess two specific binding sites, one for the week, while the maltases that act only on a maltose substrate and one for Na+. The rate of sugar substrate could not be detected. transport seems to be dependent on the difference Foetal meconium had a high enzyme activity, between intracellular and extracellular Na concen- probably originating from desquamated mucosal trations, and the driving force is derived from the cells, but the meconium obtained shortly after birth Na concentration gradient, which is maintained by from term infants was devoid of disaccharidases. an ouabain-sensitive mechanism. Czaky's hypo- Alkaline phosphatase, which seems to be more thesis, however, suggests that it is the energy yielding stable, was extremely active. system which requires intracellular Na for its In some mammals such as rats, pigs, and cows, activation and which is inhibited by the cardiac lactase activity is highest in the newborn and glycosides. The pump part is then an ATP- Arch Dis Child: first published as 10.1136/adc.42.224.341 on 1 August 1967. Downloaded from

344 A. Holzel adenosine triphosphatase-sodium complex with a likely to be more severe in the infant at the breast or specific carrier for sugar. According to Semenza, on cow's milk formulae enriched with lactose. Tosi, Vallotton-Delachaux, and Mulhaupt (1964), Deficient hydrolysis of the sugar leads to its human intestinal sucrase is also activated by Na, retention in the gut and to an influx of large and a mechanism similar to that of glucose absorp- quantities of water to balance the increase in tion might be responsible for the transport of osmotic pressure. sucrose. Bacterial fermentation of the unabsorbed lactose Actively transported sugars move far faster than a produces appreciable quantities of short-chain fatty sugar such as fructose which crosses the cell acids, which account for the low pH of the sour membrane by diffusion. smelling, frothy, loose, or watery stools. Intestinal Disturbances of the transport mechanism have colics and extensive excoriation of the buttocks add recently been implicated in the pathogenesis of to the clinical features to form a fairly characteristic serious metabolic disorders in infancy. picture. Since the patients with primary lactase deficiency Deficient Lactase Activity (hypolactasia or alactasia) are young infants, in only Among the disaccharidase deficiencies, diminished a few cases has the diagnosis been supported by or absent, lactase activity is the most important. estimation of 3-galactosidase activity in peroral The congenital and probably hereditary type is rare biopsy specimens of intestinal mucosa (Davidson in childhood, but the acquired type has been found et al., 1964; Lifshitz, 1966; Launiala et al., 1966). associated with a large number of unrelated gastro- intestinal disorders. Lactase seems to be by far the Lactase deficiency in the adult. A syndrome most sensitive of sugar-splitting enzymes in the not unlike that seen in young infants with deficient brush-border of the small intestinal mucosa. lactase activity was first described in adults by Maybe because of its spatial localization it is both Haemmerli, Kistler, Ammann, Auricchio, and more easily damaged than the other disaccharidases, Prader (1963), Haemmerli, Kistler, Ammann, Marthaler, Semenza, Auricchio, and Prader (1965), and takes longer to recover function if the injury is copyright. reversible. and Auricchio, Rubino, Landolt, Semenza, and Prader (1963b). They recognized that lactose Congenital alactasia (hypolactasia). The malabsorption was the basis of the clinical first observation of primary, congenital, and most manifestations of milk intolerance previously likely hereditary, deficient lactose absorption in two diagnosed in a number of patients who, two hours sibs was made by Holzel, Schwarz, and Sutcliffe after milk ingestion, developed abdominal colic, (1959), who introduced the lactose tolerance test as flatulence, and watery diarrhoea. Removal of

circumstantial evidence for lactase activity; follow- lactose from the diet brought them rapid relief. http://adc.bmj.com/ ing a lactose loading dose the rise of the blood Enzyme studies of intestinal biopsy specimens glucose level was small compared with that after a proved the absence of lactase activity in an otherwise glucose-galactose load. 18 cases have subsequently morphologically normal mucosa. These observa- been recorded, of which 15 have been boys and 3 tions have been confirmed by Cuatrecasas, Lock- girls (Weijers, van de Kamer, Dicke, and Ijsseling, wood, and Caldwell (1965), Dunphy, Littman, 1961; Holzel, 1962, 1965; Thornton, Burkinshaw, Hammond, Forstner, Dahlqvist, and Crane (1965), and Kawerau, 1962; Davidson, Sobel, Kugler, and Peternel (1965), and McMichael, Webb, and Prader, 1964; Durand and La medica, 1962; Dawson (1965). on September 26, 2021 by guest. Protected Lifshitz, 1966; Launiala, Kuitunen, and Visakorpi, It has been pointed out, however, that not all 1966). adults with deficient lactase activity had clinical manifestations when given lactose. Nor did its Familial incidence and genetic factors. Three removal alleviate symptoms in other patients who pairs of sibs were found with the condition, but despite normal lactase could not take milk without there have been no cases with consanguineous discomfort. Since signs of milk intolerance had parents. not been evident during early childhood, it was Clinical picture. Diarrhoea, as in all the disac- postulated that the lactase-deficient patients had charidase malabsorptions, is the main feature, and acquired the defect later in life. There are, starts within a few days after birth as soon as milk however, few observations that would allow a feeding is well established. Since the lactose con- rational interpretation of pathogenetic factors tent of the food is the factor determining the severity occurring in older children or adults. A large of the alimentary tract manifestations, these are number of diseases of the alimentary tract have now Arch Dis Child: first published as 10.1136/adc.42.224.341 on 1 August 1967. Downloaded from

Sugar Malabsorption 345 been found to be accompanied by reduced or by Durand in 1958 under the title of 'Lattosuria impaired disaccharidase activity, but in general these idiopathica in una paziente con diarrea cronica ed have been associated with inflammatory or trophic acidosi'. He published the biochemical data of the changes in the intestinal mucosa, usually reversible case in greater detail in 1959. The two papers with improvement of the primary condition. A contain the case history of a 13-month-old girl of decrease in lactase activity from birth to the end of consanguineous parents who had recurrent episodes the suckling period, and continuing to a low level of diarrhoea from the first few days of life, accom- in the adult, has been observed in various animals, i.e. panied by a heavy lactosuria, minor degrees of the pig, calf, rabbit, and rat, and to some extent in the proteinuria, renal acidosis, failure to thrive, and cat and dog. This, however, does not apply to the eventual death at the age of 15 months. Necropsy human species (see above), nor is there any support showed an atrophic enteritis with degenerative for the concept that feeding large amounts of atrophic changes in adrenals, liver, and convoluted lactose may lead to an increase of lactase activity, as tubules in the kidney. Among other explanations reported in rats (Girardet, 1965; Cuatrecasas et al., Durand suggested the possibility of an intestinal 1965). Genetic aspects have therefore been scru- lactase deficiency as the cause of the disease. tinized more closely and their significance stressed. Darling, Mortensen, and S0ndergaard (1960) published records of two related infants suffering Racial factors. Of the 41 American Negroes from diarrhoea, vomiting, and failure to thrive, studied by Cuatrecasas et al. (1965), 30 were lactose associated with lactosuria and aminoaciduria, with non-absorbers. This high incidence of lactase death at a few weeks of age. Short periods of deficiency in the American Negro induced Cook and lactose-free diet had led to the disappearance of the Kajubi (1966) to examine its tribal distribution in mellituria, but did not seem to influence the course Uganda. They found lactase deficiency to be appreciably. A case of congenital lactose intoler- common in Baganda children and adults, and also ance in a 2-year-old child with lactosuria, renal among members of other Bantu tribes. Patients acidosis, increase in blood urea, vomiting, and with Hamitic ancestry from Rwanda and Ankole had failure to thrive, was recognized by Fois, Vedovini, much higher levels of activity. Tribal cultures and and Marinello (1961): recovery followed a lactose- copyright. habits may have been influenced by lactase levels, free regimen. Congenital lactosuria occurring as a since the Hamites studied were cattle owners and familial fatal disease in 3 sibs (Jeune, Charrat, lived mainly on milk, whereas the Baganda are an Cotte, Fournier, and Hermier, 1960) illustrates its agricultural society who lived mainly on a vegetable gravity. A lactose-free diet ensured recovery in a diet. The incidence of lactase deficiency in the number of cases (Fois et al., 1961; Inall and American Negro was further studied by Bayless and Burkinshaw, 1960; Holzel, Mereu, and Thomson, Rosenzweig (1966) with 40 healthy, well-nourished 1962). volunteers. 7000 of the Negroes had low levels of It has been suggested that this disorder is a more http://adc.bmj.com/ activity, compared with 5% of the Caucasians. severe form of deficient lactase activity and lactose McMichael et al. (1965, 1966), referring to a malabsorption, but our studies lead to the view that personal communication by Moskoutis regarding congenital (familial) lactose intolerance is an entirely the great frequency of lactase deficiency among different clinical and pathological entity, with a Greeks, point out that 15 out of 17 Greek Cypriots separate pathogenesis, pathophysiology, and progno- living in London whose lactose tolerance was tested sis. There may be some similarity in symptomato- also had lactase deficiency. The experience of

logy, since a temporary reduction of lactase activity on September 26, 2021 by guest. Protected Jeejeebhoy, Desai, and Verghese (1964) with may be part of some process interfering with the patients suffering from sprue indicates that deficient more general absorptive functions and an increased lactase activity is not uncommon in the Indian permeability of the small intestinal mucosa. The population, though this relates to special circum- associated sucrosuria, glucosuria, and steatorrhoea stances. Its occurrence as a post-gastrectomy are in keeping with such a view. The gastro- complication transcends racial limits and has mainly intestinal manifestations are mainly vomiting and been reported in Caucasians (Hooft, van Hauwaert, only to a lesser extent diarrhoea; renal involvement de Laey, and Adriaenssens, 1963; Plotkin and can be deduced from the presence of acidosis, Isselbacher, 1964). aminoaciduria, mellituria, and a rise in blood urea. Haemorrhagic complications are not unusual in the Familial lactose intolerance. Discussions of untreated patient whose condition is precarious. the published material on lactose malabsorption The disease is self-limiting, and tolerance for often make reference to a syndrome first described lactose may return 6-18 months after the onset. Arch Dis Child: first published as 10.1136/adc.42.224.341 on 1 August 1967. Downloaded from

346 A. Holzel Too early resumption of milk feeding may end in the abnormal gene. Four families, each with a catastrophe. child suffering from sucrose-isomaltose absorption, The reasons for regarding 'familial lactose intol- were submitted to peroral intestinal biopsies, and erance' as a separate entity are: (1) difference in the values of the disaccharidase assay were compared clinical pattern; (2) the presence of lactosuria which with those obtained in a group of normal adults and is absent in even the severe forms of deficient children. All the parents of the affected children lactase activity; (3) the satisfactory rise in blood had intestinal sucrase and isomaltase levels below glucose levels following lactose-loading doses during the average found in the control group. When the the active phase of the disease (Darling et al., 1960; levels of the enzymes were expressed as ratios to Fois et al., 1961; Holzel et al., 1962); (4) the return lactose they differed significantly from the control to normal lactose absorption after brief periods of group. The authors therefore concluded that lactose-free diet, with exacerbation of lactose sucrase-isomaltase deficiency was a recessively- intolerance if lactose feeding continues; (5) the transmitted disorder. self-limiting nature of the disorder, hardly compa- A special problem in this hereditary condition is tible with a hereditary enzyme defect; and (6) the constant association of two enzyme defects. lactase activity demonstrated to be normal after According to Dahlqvist (1962) the two activities are recovery (Holzel, 1967). attributable to separate enzymes. To reconcile the available facts with the 'one gene one enzyme Primary Sucrase-Isomaltase Deficiency hypothesis', is somewhat puzzling. However, if it The description by Weijers et al. (1961) of a be assumed that one defective structural element diarrhoeal disorder in children due to sucrose may possess two active side chains for different malabsorption was soon followed by others. substrates this would readily explain the data Prader, Auricchio, and Murset (1961), Delaitre, (Launiala et al., 1964). Fonty, Varlet, and Fourrier (1961), Auricchio et al. (1961), Auricchio, Dahlqvist, Miirset, and Prader Clinical features. Diarrhoea, the most con- (1962), and Auricchio, Dahlqvist, Murset, and stant symptom in all the sugar malabsorption

Prader (1963a), Auricchio, Rubino, Prader, Rey, Jos, syndromes, follows the introduction of sucrose and copyright. Freza], and Davidson (1965b) demonstrated the starch into the infant's diet. In the breast-fed simultaneous occurrence of isomaltase deficiency in infant this is likely to be at a later date than in the their patients, and this was confirmed by investigators bottle-fed one. Though many of the commercially in different parts of the globe (Anderson, Messer, prepared baby foods contain only lactose, starch is Townley, and Freeman, 1963; Rey, Frezal, Jos, now being offered at an increasingly early age. The Bauche, and Lamy, 1963; Burgess, Levin, persistence of the fermentative diarrhoea is accom- Mahalanabis, and Tonge, 1964; Launiala, panied by a failure to thrive, which is never as Perheentupa, Visakorpi, and Hallman, 1964; Nordio marked as in the cases with lactase deficiency. http://adc.bmj.com/ and La medica, 1964; Sonntag, Brill, Troyer, Welsh, Some patients manifest also minor degrees of Semenza, and Prader, 1964; Townley, Khaw, and steatorrhoea (Nordio, La medica, and Vignolo, 1961; Shwachman, 1965; Semenza, Auricchio, Rubino, Anderson et al., 1963; Francois, Frederich, Vicens- Prader, and Welsh, 1965b). Calvet, Bertrand, and Ruitton-Ugliengo, 1963; Rey In recent reviews of the condition, the number of et al., 1963; Gorouben, Bedu, Le balle, Grumbach, published cases has been given as 40 by Townley Yonger, Weill, and Kaplan, 1963; Burgess et al., (1966), while Prader and Auricchio (1965) know of 1964; Lifshitz and Holman, 1964). Spontaneous 63 cases, 34 male and 29 female, among them only improvement has been known to occur (Auricchio on September 26, 2021 by guest. Protected 5 adults. et al., 1961), but in the vast majority of patients Genetics. The mode of inheritance has yet to dietary adjustment, such as the replacement of be established. A dominant trait was initially sucrose and starch by glucose, is enough to bring suggested (Auricchio et al., 1961), but a recessive about lasting improvement. disorder seems probable, since there are at least 10 records of affected sibs and 2 of consanguineous Diagnosis of Disaccharidase Deficiencies parents (Prader and Auricchio, 1965). One of the This should be considered whenever there is a difficulties in establishing the recessive nature of the history of diarrhoea, with onset in early infancy. condition is the recognition of the heterozygote. Marked malnutrition will only be encountered in the Kerry and Townley (1965) decided to use the more severe forms and is more likely to be the result quantitative assay of disaccharidase in small bowel of lactase deficiency than of defective sucrase and biopsy specimens for the detection of the carrier of isomaltase activity. The frothy appearance of the Arch Dis Child: first published as 10.1136/adc.42.224.341 on 1 August 1967. Downloaded from

Sugar Malabsorption 347 stools and their sour smell may arouse the first flat lactose tolerance curve, and Kern and Struthers suspicion of such a disorder. (1966) found that in these cases the intraduodenal administration of 30 g. lactose in 300 ml. water in Faecal pH. The faecal pH can be used as a 30 minutes caused a normal rise of blood glucose. screening test, but is not very reliable since it may Peternel (1965), in evaluating the oral lactose also be lowered in infective forms of gastro- tolerance test as a screening test, found a good enteritis, and may occasionally be normal. In serial correlation between an increase in blood glucose stool examination on several adult patients with greater than 20 mg./100 ml. above the fasting level, hypolactasia, McMichael et al. (1965) found that the with normal lactase activity. Girardet and Richte- pH fluctuated, and that not even after lactose rich (1962) failed to obtain a rise in glucose blood administration was a low value registered. Values levels in some healthy adults after lactose loading, were similar to those found in 14 control patients, and this may occasionally happen. In our experi- and in no patient was a random pH of less than 5 - 7 ence, lactose tolerance tests can be usefully employed recorded. However, in infants on cows' milk feeds iftheir results are reproducible. To a large measure, the stool has a pH between 6 * 5 and 7 * 5, while in the this applies also to other disaccharide loading tests, fermentative diarrhoeas it is below 6 and sometimes in particular to sucrose tolerance tests. An increase closer to 5. of blood glucose of more than 30 mg./100 ml. above fasting level at any point of the tolerance curve may Lactic acid in faeces. Since the fall in pH is be regarded as an indication ofnormal disaccharidase the result of the formation of large quantities of low activity, values that do not exceed 20 mg. usually molecular weight organic acids, the estimation of denoting impaired absorption. An increase of lactic acid has been recommended as a useful test. 20-30 mg./100 ml. above fasting level is of doubtful Lactic acid can be determined by enzymatic or significance. chemical methods; a simple technique has been It is important to carry out control tests with the developed by Clarke and Podmore (1966). corresponding component monosaccharides mixed Although increase in lactic acid excretion may in equal parts to eliminate disturbances with similar occur in other forms of diarrhoea, and cannot there- symptomatology but different pathogenesis, such as copyright. fore be regarded as specific, a healthy child on a the glucose-galactose malabsorption syndromes, or normal diet rarely excretes more than 35 mg. lactic conditions associated with a gross general reduction acid per 24 hours. By contrast, in a fermentative of small intestinal absorptive capacity. Congenital diarrhoea several grammes may be excreted in the monosaccharide malabsorption has not been reported course of 24 hours (Weijers and van de Kamer, in adults and the control tests have therefore less 1964), and the finding of more than 50 mg. lactic significance. Fat balance studies, xylose excretion, acid in a random sample of 100 g. faeces can be etc. have to be employed to excJude disaccharidase taken to indicate excess fermentation. deficiencies secondary to other causes of mal- http://adc.bmj.com/ Determination of the total content of low molecu- absorption (Anderson, 1966). lar weight volatile fatty acids (Weijers and van der Kamer, 1964) provides no more reliable evidence Sugar excretion in the urine. Excluding the than the tests mentioned; no increase was found in minute quantities that occur physiologically, this is lactase-deficient adults (McMichael et al., 1965). not raised in the primary disaccharidase deficiencies, but is present to an appreciable degree in lactose

Sugar-loading tests. If carried out in the intolerance (see above). The faeces, however, may on September 26, 2021 by guest. Protected absence of diarrhoea, these tests are extremely useful contain increased amounts of the disaccharide or, in the assessment of disaccharidase activity. The under special bacteriological conditions, also the recommended dose of sugar administered orally is monosaccharides. Chromatographic demonstration 2 g./kg. body weight or 50 g./m.2 body surface area. of the sugars in the faeces and urine may prove a It makes little difference which of the two standards valuable diagnostic aid. Application of the 'clini- one accepts, provided it is maintained. It seems test' to the liquid part of the motions was suggested advisable to precede the test for a few days with a as a helpful screening procedure in cases suspected diet rich in carbohydrates. Since absorption is of disaccharide malabsorption by Burke, Kerry, and influenced by a variety of factors besides disacchari- Anderson (1965). dase activity, as for instance the rate of gastric emptying, the standard use of a 10% solution of the Radiological diagnosis. Recently an attempt required sugar is probably wise (Girardet, 1965). has been made to exploit radiography in the recogni- In some adults slow gastric emptying may lead to a tion of sugar malabsorption, by utilizing a suspen- Arch Dis Child: first published as 10.1136/adc.42.224.341 on 1 August 1967. Downloaded from

348 A. Holzel sion of micropaque barium sulphate with 25 g. of TABLE III lactose or other sugars, according to the suspected Disaccharide Activity (units/g. protein) in enzyme deficiency. Laws and Neale (1966) found Jejunal Mucosa in Normal Children characteristic changes: the small intestine appeared (Burke et al., 1965) distended by dilute contrast medium; peristalsis was very active, the contrast medium reaching the Lactase Sucrase Isomaltase Maltase transverse or descending colon within an hour; II while the haustral pattern was strikingly prominent. Range 1 4-132 32-228 31-177 83-615 Quantitative biochemical assay of disaccharidases Mean 49 95 89 260 in peroral biopsy specimens of intestinal mucosa is regarded as the most reliable diagnostic means. The technique, difficulties, and limitations ofperoral Burgess et al. (1964) expressed the unit of enzyme biopsy have been very fully discussed by Anderson activity as equal to the hydrolysis in ,umole of (1966). Since only a tiny fraction of intestinal substrate/g. wet mucosa per minute; the values ob- mucosa is examined, one may obtain entirely tained in normal children are given in Table IV. misleading information, particularly in disacchari- Choosing the same standard, Holzel (1966) found dase deficiencies secondary to diseases of the small the values ranging for lactase, 5-12; for maltase, gut. In conditions where the proximal part is more 34-70; and for sucrase, 7-21. Recently Messer and heavily involved than the distal, one may be faced Dahlqvist (1966) described a one-step ultramicro with the conflicting results of tolerance tests and method for the assay of intestinal disaccharidases, enzyme assay, namely that disaccharide absorption which is more suitable for the small quantities of may be taking place even in the seemingly complete mucosa removed by peroral biopsy than the two- absence of the sugar-splitting enzymes. Alterna- step method originally developed by Dahlqvist tively, a variety of agents may temporarily inhibit (1964a, b). enzyme activity, but the resulting sugar malabsorp- TABLE IV tion may be only one minor consequence of an Disaccharide Activity (units/g. wet mucosa per underlying gross inflammatory process. minute) in Jejunal Mucosa in Normal Children copyright. Prader and Auricchio (1965) give the following (Burgess et al., 1964) figures for the disaccharidase activities in the mucosa of the jejunum of the adult obtained by Lactase Maltase Sucrase biopsy (Table II). The enzyme activity is expres- Range 7-12 43-90 12-20 sed in units per g. protein; each unit splits one Mean 8 -7 62 -6 17 *4 micromole substrate per minute.

TABLE II Acquired Disaccharide Malabsorption http://adc.bmj.com/ Disaccharide Activity in Jejunal Mucosa in With the knowledge that the disaccharidases were Normal Adults (Prader and Auricchio, located in the exposed position of the brush-border 1965) of the mucosal epithelium, intensive investigation Enzyme Activity (units/g. protein) of all those disorders associated with structural Disaccharidase Mean changes of the intestinal mucosa for sugar mal- Range absorption has revealed a large number of secondary Maltase .593 310-1120 Sucrase .173 70-325 disaccharidase deficiencies, both in children and on September 26, 2021 by guest. Protected Isomaltase .159 65-268 Lactase .107 39-258 adults. Lactase was far more commonly deficient Cellobiase .14 9-21 than other disaccharidases, particularly amongst adults. In children, reduced or absent activity related often to two or even three of the hydrolytic These authors also point out that though there is enzymes. great variation in the absolute values of disacchari- Secondary lactase deficiency in adults (Haemmerli dase activity, the ratios between the various enzymes et al., 1965) has been encountered following gastro- are constant with the exception of lactase activity. jejunostomy (Gryboski, Thayer, Gryboski, Gabriel- Maltase activity is three to four times higher than son, and Spiro, 1963), bowel resection (Kern, sucrase or isomaltase, and the latter about three to Struthers, and Attwood, 1963), and various other four times higher than lactase activity. Burke et al. affections of the gut. Combined disaccharidase (1965) gave the normal range of disaccharidase deficiences were common in coeliac disease of the activity in jejunal mucosa in children (Table III). adult (Plotkin and Isselbacher, 1964). In children, Arch Dis Child: first published as 10.1136/adc.42.224.341 on 1 August 1967. Downloaded from

Sugar Malabsorption 349 the most striking form of deficient disaccharidase Giardiasis. Lactose malabsorption in heavy activity is associated with gluten-induced entero- infestation with Giardia intestinalis has been recor- pathy (Holzel, 1964; Shmerling, Auricchio, Rubino, ded by Durand (1964), Nordio, La medica, and Hadorn, and Prader, 1964; Nordio, La medica, Vignolo (1963), and Holzel (1967). Depres- Vignolo, and Berio, 1965; Arthur, Clayton, Cottom, sion of lactase activity may occur as an isolated Seakins, and Platt, 1966; Lubos, Gerrard, and phenomenon, or as part of the more general reduc- Buchan, 1967). Our studies and those of other tion of disaccharidase activity. Mucosal biopsy in workers agree on the fact that during the florid phase our cases showed only minor degrees of inflamma- of the illness, when the surface structures of the tory reaction with no major alteration in the mucosal small intestinal mucosa are considerably disor- pattern. Eradication of the infection was followed ganized, disaccharide absorption is grossly impaired. by very slow recovery of enzyme function. Lactose tolerance is much more reduced than that of other disaccharides, and malabsorption of this sugar Gastro-enteritis. Intolerance to milk following persists for much longer than that of the other infective forms of gastro-enteritis was known to the common disaccharides. Patients with inadequate paediatricians of the early decades of this century, dietary control, and in relative well-being though but the protein and fat constituents were then with some delay in growth, have been able to regarded as causing the damage. Sunshine and absorb glucose at a normal rate but have shown flat Kretchmer (1964) and Burke et al. (1965) produced disaccharide tolerance curves. It seems, therefore, laboratory evidence that dietary lactose was the that disaccharide loading tests can be used as a noxious factor in the persistent diarrhoea in these, further tool in the assessment of absorptive recovery. cases. The occurrence of crises has in some of our coeliac patients been related to an increased intake of lactose. In one patient, enzyme assay of the Monosaccharide Malabsorption intestinal mucosa specimen showed almost complete It is not unknown for the same important absence of lactase activity. A lactose- and gluten-

scientific observation to be made by independent copyright. free diet led to elimination of the crises and scientific workers at the same time in different parts uninterrupted progress towards recovery. The rou- of the world. Preoccupation with similar topics of tine imposition of lactose-, sucrose- and gluten-free research is a common feature in the Western nations diets (Arthur et al., 1966) on every child with and probably more the result of modern means of coeliac disease may place an unnecessarily heavy communication than of the influence of a genius burden on hospital and home, but where a gluten- mundi. free diet alone does not achieve the desired result, It is nevertheless interesting to record that removal of the disaccharides may hasten recovery. Lindquist, Meeuwisse, and Melin (1962) and http://adc.bmj.com/ The disacchariduria in these patients (Arthur et al., Lindquist and Meeuwisse (1962) in Sweden 1966) is more likely an expression of the severity of recognized a new disorder of monosaccharide mucosal damage than an index of disaccharide malabsorption more or less simultaneously with the intolerance (Prader, Shmerling, and Hadorn, French authors, Laplane, Polonovsky, Etienne, 1966). Debray, Lods, and Pissarro (1962). It was rightly named glucose-galactose malabsorption by Lind- Kwashiorkor. Protein-calorie malnutrition is quist and his colleagues, who realized that basically another disorder that includes in its symptom it was probably due to some major disturbance of on September 26, 2021 by guest. Protected complex severe and often persisting diarrhoea. the absorptive mechanism, and they, as well as the Bowie, Brinkman, and Hansen (1965) demonstrated French workers, assumed a congenital disturbance that children suffering from the condition could of the active transfer mechanism. Since then absorb monosaccharides satisfactorily, but seemed further cases have been published in Germany intolerant of disaccharides; exclusion from the diet (Linneweh, Schauml6ffel, and Barthelmai, 1965), resulted in control of the diarrhoea. Cook and Lee Australia (Anderson, Kerry, and Townley, 1965), (1966), in an attempt to assess the degree of recovery U.S.A. (Schneider, Kinter, and Stirling, 1966; of disaccharidase activity, examined 7 Baganda and Marks, Norton, and Fordtran, 1966), and Belgium 13 Bahutu children 4-10 years after diagnosis and (Eggermont and Loeb, 1966). At least 11 well- treatment of kwashiorkor. Lactase levels in 18 documented cases prove the wide distribution of biopsy specimens were low. Lactase deficiency was this inborn error of metabolism; familiarity with its confirmed in 17 children by tolerance tests. All clinical manifestation will in due course lead to a other disaccharidases were within normal limits. true assessment of its incidence. Arch Dis Child: first published as 10.1136/adc.42.224.341 on 1 August 1967. Downloaded from

350 A. Holzel Clinical picture. There is severe watery succeeded in determining the residual enzyme diarrhoea starting in the first week of life, leading to activity in their patient with monosaccharide mal- rapid and life-threatening dehydration. The faeces absorption; it was 7 6% for glucose and 4 6% for contain large quantities of sugars and lactic acid; galactose. Dietary treatment can be successfully the urine may also contain reducing substances in carried out with a formula consisting of casein, corn small amounts. The gravity of the condition oil, and fructose, with adequate vitamin comple- varies; it may cause death in the untreated, or if less ments. A rather ill-defined form ofmonosaccharide severe may produce a severe marasmus accompanied malabsorption of a transitory nature in young by chronic diarrhoea. The most telling feature is infants has recently been reported from Australia probably the almost instantaneous cessation of the (Burke and Danks, 1966). Although these babies explosive diarrhoea when oral feeds are stopped, were thoroughly investigated, the results did not only to start again if foods containing monosacchar- allow any aetiological or pathogenetic conclusions. ides other than fructose or disaccharides are given, which by hydrolysis lead to the breakdown to The rapidly expanding knowledge of the enzy- monosaccharides. Familial incidence was observed matic mechanism involved in sugar absorption and by Lindquist et al. (1962), Laplane et al. (1962), and its disturbances has by no means reached its limits, Anderson et al. (1965). Routine laboratory in- and no doubt further development will add to a vestigations of the faeces for pathogens are generally better understanding of the physiological processes involved. unhelpful. Slight steatorrhoea was observed in one REFERENcES patient only. A glucose or galactose loading test Anderson, C. M. (1966). Intestinal malabsorption in childhood. did not produce an adequate rise in blood glucose Arch. Dis. Childh., 41, 571. -, Kerry, K. R., and Townley, R. R. W. (1965). An inborn levels, in contrast to fructose which caused an defect of intestinal absorption of certain monosaccharides. increase of both glucose and fructose in the blood. ibid., 49, 1. -, Messer, M., Townley, R. R. W., and Freeman, M. (1963). Dehydration was associated with disturbances of Intestinal sucrase and isomaltase deficiency in two siblings. electrolyte and nitrogen balance. Peroral biopsy Pediatrics, 31, 1003. specimen showed normal disaccharidase activity, Arthur, A. B., Clayton, B., Cottom, D. G., Seakins, J. W. T., and

Platt, J. W. (1966). Importance of disaccharide intolerance in copyright. and seemed structurally normal. the treatment of coeliac disease. Lancet, 1, 172. Auricchio, S., Dahlqvist, A., Murset, G., and Prader, A. (1962). In view of the tolerance for fructose, with its Intestinal isomaltase deficiency in patients with hereditary different mode of absorption, it was a fair assump- sucrose and starch intolerance. ibid., 1, 1303. tion that the active carrier system might be at fault, and - (1963a). Isomaltose intolerance causing decreased ability to utilize dietary starch. J. Pediat., 62, 165. and a good deal ofevidence has been brought forward -, Prader, A., Murset, G., and Witt, G. (1961). Saccharosein- in its support. Loading tests with 3-0-methylglu- toleranz. Durchfall infolge hereditiren Mangels an intestinaler Saccharaseaktivitat. Helv. paediat. Acta, 16, 483. cose (Anderson et al., 1965), a synthetic sugar with -, Rubino, A., Landolt, M., Semenza, G., and Prader, A. (1963b). the requisite configuration for active transport, Isolated intestinal lactase deficiency in the adult. Lancet, 2, 324. http://adc.bmj.com/ showed failure of absorption. The application of -, -, and Murset, G. (1965a). Intestinal glycosidase activities autoradiography to fresh specimens of intestinal in the human embryo, foetus and newbom. Pediatrics, 35, 944. mucosa with 14C-labelled galactose in a -,, - , Prader, A., Rey, J., Jos, J., Frezal, J., and Davidson, M. special (1965b). Intestinal glycosidase activities in congenital mal- medium, demonstrated the inability of the cells of absorption of disaccharides. J. Pediat., 66, 555. the patient's mucosa to accumulate the galactose, -, Semenza, G., and Rubino, A. (1965c). Multiplicity of human intestinal disaccharidases. II. Characterization ofthe individual while the uptake succeeded in the control specimen. maltases. Biochim. biophys. Acta (Amst.), 96, 498. Eggermont and Loeb (1966) tried to prove that Bayless, T. M., and Rosenzweig, N. S. (1966). Lactase deficiency in Uganda. Lancet, 2, 225. glucose-galactose malabsorption was the result of a Borgstrom, B., Dahlqvist, A., Lundh, G., and Sjovall, J. (1957). on September 26, 2021 by guest. Protected derangement of the sodium-dependent active Studies of intestinal digestion and absorption in the human. transport. Meeuwisse and Dahlqvist (1966) ob- J. clin. Invest., 36, 1521. Bowie, M. D., Brinkman, G. L., and Hansen, J. D. L. (1965). tained intestinal biopsy specimens from 2 patients Acquired disaccharide intolerance in malnutrition. J. Pediat., with this disorder. The mucosa appeared normal 66, 1083. Burgess, E. A., Levin, B., Mahalanabis, D., and Tonge, R. E. (1964). on light microscopy. On incubation of the Hereditary sucrose intolerance: levels of sucrose activity in specimens with 14C-labelled glucose there was no jejunal mocosa. Arch. Dis. Childh., 39, 431. in the tissue than Burke, V., and Danks, D. M. (1966). Monosaccharide mal- greater accumulation of the sugar absorption in young infants. Lancet, 1, 1177. in the medium, while in control experiments -, Kerry, K. R., and Anderson, C. M. (1965). The glucose in the mucosa was 4 times as high as that in relationships of dietary lactose to refractory diarrhoea in infancy. Aust. paediat. J., 1, 147. the medium. They are also of the opinion that the Burkinshaw, J. H. (1960). Lactosuria and sucrosuria with failure defect is in the glucose-galactose specific carrier. to thrive. Proc. roy. Soc. Med., 53, 318. Cajori, F. A. (1933). The enzyme activity of dogs' intestinal juice In a special study with 14C-labelled sugars, and its relation to intestinal digestion. Amer. J. Physiol., 104, Linneweh, Schauml6ffel, Graul, and Bode (1966) 659. Arch Dis Child: first published as 10.1136/adc.42.224.341 on 1 August 1967. Downloaded from

Sugar Malabsorption 351 Clarke, A. D., and Podmore, D. A. (1966). The enzymatic deter- Girardet, P. (1965). Absorption et Malabsorption du Lactose. mination of lactic acid in faeces in glycosidase deficiency. H. Huber, Berne and Stuttgart. Clin. chim. Acta, 13, 725. -, and Richterich, R. (1962). A propos de l'alactasie congenitale Cook, G. C., and Kajubi, S. K. (1966). Tribal incidence of lactase et des courbes de surcharge au lactose. Ann. paediat. (Basel), deficiency in Uganda. Lancet, 1, 725. 198, 127. -, and Lee, F. D. (1966). The jejunum after kwashiorkor. Gorouben, J. C., Bedu, J., Le balle, J. C., Grumbach, R., Yonger, ibid., 2, 1263. J., Weill, J., and Kaplan, M. (1963). L'intolerance au Cuatrecasas, P., Lockwood, D. H., and Caldwell, J. R. (1965). saccharose. Etude clinique et biologique de 5 cas. Arch. Lactase deficiency in the adult: a common occurrence. ibid, 1, franc. Pediat., 20, 253. 14. Gray, G. M., and Ingelfinger, F. J. (1965). Intestinal absorption Dahlqvist, A. (1962). Specificity of the human intestinal disac- of sucrose in man: the site of hydrolysis and absorption. charidases and implications for hereditary disaccharide intoler- J. clin. Invest., 44, 390. ance. J. clin. Invest., 41, 463. Greaves, J. P., and Hollingsworth, D. F. (1964). Changes in the (1964a). Intestinal disaccharidases. In Disorders due to pattern of carbohydrate consumption in Britain. Proc. Nutr. Intestinal Defective Carbohydrate Digestion and Absorption, Soc., 23, 136. ed. P. Durand. I1 Pensiero Scientifico, Rome. Gryboski, J. D., Thayer, W. R., Jr., Gryboski, W. A., Gabrielson, - (1964b). Method for assay of intestinal disaccharidases. I. W., and Spiro, H. W. (1963). A defect in disaccharide Analyt. Biochem., 7, 18. metabolism after gastrojejunostomy. New Engl. J. Med., 268, -, Auricchio, S., Semenza, G., and Prader, A. (1963). Human 78. intestinal disaccharidases and hereditary disaccharide intoler- Haemmerli, U. P., Kistler, H. J., Ammann, R., Auricchio, S., and ance. The hydrolysis of sucrose, isomaltose, palatinose Prader, A. (1963). Lactasemangel der Dusmdarmmucosa als (isomaltulose) and a 1, 6-a-oligosaccharide (iso-malto- Ursache gewisser Formen erworbener Milchintoleranz beim oligosaccharide) preparation. J. clin. Invest., 42, 556. Erwachsenen. Helv. med. Acta, 30, 693. -, and Borgstrom, B. (1961). Digestion and absorption of Marthaler, T., Semenza, G., Auricchio, S., and disaccharides in man. Biochem. J., 81, 411. Prader, A. (1965). Acquired milk intolerance in the adult -, and Brun, A. (1962). A method for the histochemical caused by lactose malabsorption due to a selective deficiency of demonstration of disaccharidase activities: application to intestinal lactase activity. Amer. J. Med., 38, 7. invertase and trehalase in some animal tissues. J. Histochem. Heilskov, N. S. C. (1956). Studies on animal lactase. Dissertation, Cytochem., 10, 294. Copenhagen. -, and Lindberg, T. (1966). 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Intestinal lactase deficiency of presumed congenital origin in ed. T. J. Thomson and I. E. Gillespie, p. 68. Bailliere, two older children (Abstr.). Gastroenterology, 46, 737. Tindall & Cassell, London. Delaitre, R., Fonty, Varlet, and Fourrier (1961). Diarrh6e (1967). Disorders of carbohydrate metabolism. J. roy. Coll. chronique chez un nourrisson par intolerance au saccharose. Phycns (Lond.), 1, 177. Arch. franc. Pidiat., 18, 1202. (1967). Disaccharide intolerances. Symposium on disorders Doell, R. G., and Kretchmer, N. (1962). Studies of small intestine of carbohydrate metabolism. Proc. of Society for the Study of during development. I. Distribution and activity of j3- Inborn Errors of Metabolism. In the press. galactosidase. Biochim. biophys. Acta (Amst.), 62, 353. -, Mereu, T., and Thomson, M. L. (1962). Severe lactose -, and - (1964). Intestinal invertase: precocious develop- intolerance in infancy. Lancet, 2, 1346. ment of activity after injection of hydrocortisone. 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352 A. Holzel , Perheentupa, J., Visakorpi, J., and Hallman, N. (1964). Overton, J., Eichholz, A., and Crane, R. K. (1965). Studies on the Disaccharidases of intestinal mucosa in a patient with sucrose organization of the brush border in intestinal epithelial cells. intolerance. Pediatrics, 34, 615. II. Fine structure of fractions of Tris-disrupted hamster Laws, J. W., and Neale, G. (1966). Radiological diagnosis of brush borders. J. cell Biol., 26, 693. disaccharidase deficiency. Lancet, 2, 139. Peternel, W. W. (1965). Lactose tolerance in relation to intestinal Lifshitz, F. (1966). Congenital lactase deficiency. J. Pediat., 69, lactase activity. Gastroenterology, 48, 299. 229. Plotkin, G. R., and Isselbacher, K. J. (1964). Secondary disac- , and Holman, G. H. (1964). Disaccharidase deficiencies with charidase deficiency in adult celiac disease (nontropical sprue) steatorrhea. ibid., 64, 34. and other malabsorption states. New Engl. J. Med., 271, 1033. 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