A n n a l s o f C linical Laboratory Science, Vol. 2, No. 4 Copyright © 1972, I n s t i t u t e for Clinical Science Enzyme Defects in the Sphingolipidoses and Their Application to Diagnosis* ROSCOE O. BRADY, M.D. Developmental and Metabolic Neurology Branch National Institute of Neurological Diseases and Stroke National Institutes of Health Bethesda, MD 20014 Chronicle methods for detecting fetuses afflicted with The first clinical indication of a heritable each of the nine now known lipid storage diseases sufficiently early in pregnancy for disorder of lipid metabolism appeared just precise genetic counseling. This paper is a over 90 years ago with Warren Tay’s de­ brief review of how these developments scription of changes in the macular region came about. Moreover, an effort is made to of the eyes of children.33 Six years later, anticipate further progress in this family Bernard Sachs reported that patients with of genetic diseases. these eye lesions were also severely re­ tarded.28 In time this condition was named Tay-Sachs disease. However, most of the Clinical Manifestations of Lipid pioneering developments in the field of Storage Diseases lipid storage diseases have arisen from in­ The signs and symptoms of patients with tensive investigations in another of these the sphingolipidoses are quite varied and conditions called Gaucher’s disease. The are functions of the nature of the accumu­ first clinical description of patients with lating lipid and the particular organs and this syndrome postdated Tay’s communica­ tissues involved in the storage process tion by only a year.14 The chemical struc­ (table I). The development of the central ture of the stored lipid was first identified nervous system may be impaired in eight in Gaucher’s disease,1 and the nature of of the nine known disorders; the apparent the explicit metabolic derangement was single exception is Fabry’s disease in which elucidated first in this sphingolipodys- neuralgias and peripheral neuropathy are trophy.7’9 Through this demonstration, an frequently encountered. If the underlying unbroken precedent regarding the under­ metabolic abnormality is less severe than a lying metabolic defect in all of the sphingo­ total loss of the requisite enzyme, patients lipidoses was established. Much practical may escape cerebral damage. Patients with benefit followed this demonstration, includ­ the so-called “juvenile” and “adult” forms ing (1) accurate diagnostic tests, (2) pro­ of Gaucher’s disease are frequently en­ cedures for identifying heterozygous car­ countered in medical clinics because of riers of the lipidoses, and (3) reliable organomegaly, thrombocytopenia, or patho­ logic fractures of the long bones and verte­ * Presented at the Applied Seminar on the Clin­ brae in whom mental function is perfectly ical Pathology of the Lipids, November, 1971. normal. Improved diagnostic procedures 285 286 BRADY TABLE I M a j o r S i g n s a n d S y m p t o m s o f t h e S phingolipidoses Gaucherrs disease Mental retardation (infantile form only), hepatosplenomegaly, hip and long bone involvement, Oil-red-O and PAS-positive lipid-laden (Gaucher) cells in bone marrow, increased serum acid phosphatase, mild anemia, and thrombocytopenia Niemann-Pick disease Generally similar to Gaucher's disease? 30 percent with cherry-red spot in macula; marrow cells (foam cells) stain for both lipid and phosphorus, cachexia Globoid leukodystrophy Mental retardation? almost total absence of myelin, severe (Krabbe's disease) gliosis, and multinucleated "globoid bodies” in white matter Metachromatic leukodystrophy Mental retardation? psychological disturbances (adult form)? decreased nerve conduction time? nerve biopsy shows yellow- brown droplets when stained with cresyl violet (metachromasia) Ceramide lactoside lipidosis Slowly progressing CNS impairment? hepatosplenomegaly; macrocytic anemia, leukopenia and thrombocytopenia due to involvement of bone marrow and spleen Fabry's disease Reddish-purple maculo-papular rash in umbilical, inguinal and scrotal areas? renal impairment? corneal opacities; peripheral neuralgias and abnormalities of EKG Tay-Sachs disease Mental retardation, amaurosis, cherry-red spot in macula, macrocephaly, neuronal cells distended with "membranous cytoplasmic bodies” Generalized gangliosidosis Mental retardation, cherry-red spot in macula (50 percent of patients), hepatosplenomegaly, foam cells in bone marrow, rarefaction of all bones and skeletal deformities now available have permitted the conclu­ X-chromosome, and therefore only the fe­ sive identification of patients with Nie- male need be a carrier in order to have a mann-Pick disease also without neuronal male child affected with this disorder. Half involvement. Except for Fabry’s disease of her sons will have the disease, 50 percent and Tay-Sachs disease, hepatosplenomegaly of her daughters will be heterozygous, and is usually observed in patients with a the others will not be involved. In order sphingolipidosis. Large lipid-laden histio­ to produce an offspring afflicted with one cytes are present in the bone marrow and of the other lipid storage diseases, both elsewhere throughout the reticuloendothe­ parents must be heterozygotes. Of four lial system. In Fabry’s disease, there is an children born to such parents on a statis­ accumulation of glycolipid in the glomeruli tical basis, one child will have the disease, of the kidney, the vascular endothelium, two will be heterozygotes, and one will be and lymphatics. In patients with Tay-Sachs uninvolved. Obviously in these disorders, disease, only the neuronal cells in the both of the sexes are equally affected. central nervous system and myenteric There are interesting clinical subtleties plexus are extensively involved.34 regarding heterozygotes. Female carriers for Fabry’s disease may have varying de­ Genetics grees of ophthalmological difficulties pri­ All of the lipid storage diseases which marily affecting the cornea. By and large, are known at the present time are trans­ heterozygotes for the other lipidoses are mitted as autosomal recessive traits with symptom-free and some speculation has the exception of Fabry’s disease. The muta­ even appeared regarding the possibility that tion in Fabry’s disease is linked to the survival advantage may be a consequence ENZYME DEFECTS IN THE SPHINGOLIPIDOSES 287 of being heterozygous for Tay-Sachs dis­ lipid component of brain.36 It was there­ ease.31 fore necessary to determine whether gluco­ cerebroside was synthesized in patients Metabolic Derangements with Gaucher’s disease instead of galacto- At least five biochemical aspects are con­ cerebroside because of faulty galactose me­ stant features of all of the lipid storage tabolism. This possibility was dispelled by diseases: (1) in all of these disorders there Thannhauser in 195035 by his demonstrat­ is an accumulation of a complex lipid in ing that there was no abnormality of galac­ various tissues of the body; (2) a portion tose tolerance in Gaucher patients. We of the structure of all of the involved lipids confirmed Thannhauser’s observation and is similar and it is called ceramide (N-fatty set about to try to decide between the acyl sphingosine) following two alternatives: (1) the possi­ bility of an overproduction of a normally [CHs—(CH2) 12—CH=CH—CH (OH) minor tissue component, or (2) an impair­ —CH( NHCOR)—CH2OH]; ment of catabolism of the accumulating glycolipid. Experiments were carried out in (3) the rate of synthesis of the stored lipid 1959 dealing with the biosynthesis of cere- in patients with these disorders is com­ brosides in spleen tissue slices obtained parable to that in non-involved humans; from various control human sources and (4) the enzymatic defect in each of the from patients with Gaucher’s disease. diseases is a deficiency of a specific hydro­ These investigations revealed that there lytic enzyme required for the degradation was no increase in the rate of cerebroside of the acculating lipid; and (5) the degree formation in the tissues obtained from of attenuation of enzymatic activity is simi­ Gaucher’s patients.37 This observation led lar in all of the tissues of an affected indi­ to the idea that a deficiency of a catabolic vidual. These important concepts should enzyme was responsible for the accumula­ be kept in mind since they constitute an tion of the lipid. In 1965, it was shown important basis for investigations which conclusively that the activity of glucocere­ have provided impressive advances towards broside /J-glucosidase was drastically dimin­ the understanding and management of the ished in tissue preparations obtained from sphingolipidos es. patients with Gaucher’s disease compared The best documentation of the funda­ with the activity of this enzyme in normal mental biochemical aspects of lipid storage humans.7’9 These experiments provided the diseases has evolved over the years in the foundation for understanding the nature of course of investigations on the etiology of the metabolic abnormality in all of the Gaucher’s disease. The lipid which accu­ presently known lipid storage diseases; viz, mulates in patients with this disease is a deficiency of a specific hydrolytic enzyme called glucocerebroside. It consists of a which catalyzes the degradation of the ac­ single molecule of glucose linked by a p- cumulating lipid. Following this initial glycosidic bond to carbon atom 1 of cera­ demonstration, the underlying abnormal mide (figure 1). In order to elucidate the enzymology was soon established for meta- nature of the metabolic abnormality in chromatic leukodystrophy,22 Niemann-Pick Gaucher’s disease, a decision was required disease,8 and Fabry’s disease.5 In time, the which involved at least three separate pos­ specific enzyme deficiency was identified sibilities. The first was the formation of in the remaining lipid storage disease (fig­ an abnormal cerebroside due to an altera­ ure 1). The metabolic lesion in the lipi­ tion of carbohydrate metabolism. It had doses are quite straight-forward with the been known since 1901 that galactocere- exception of Tay-Sachs disease.