2842 Med Genet 1993; 30: 284-288

Phenylketonuria: variable phenotypic outcomes of the R261Q and maternal PKU in J Med Genet: first published as 10.1136/jmg.30.4.284 on 1 April 1993. Downloaded from the offspring of a healthy homozygote

Sandra Kleiman, Lina Vanagaite, Jeanna Bernstein, Gerard Schwartz, Nathan Brand, Avraham Elitzur, Savio L C Woo, Yosef Shiloh

Abstract the synthesis or of its cofactor, (PKU) and benign tetrahydrobiopterine. HPA with phenylala- hyperphenylalaninaemia (HPA) result nine levels of 12 mmol/l or higher is usually from a variety of in the gene expressed as the autosomal recessive disease for the hepatic enzyme phenylalanine phenylketonuria (PKU). PKU patients suffer hydroxylase. PKU has been found in the from severe mental retardation unless diag- Israeli population in two variants, classi- nosed soon after birth and treated with a low cal and atypical. The two are clinically phenylalanine diet throughout adolescence. indistinguishable and require treatment Phenylalanine levels of 0-24 to 1 1 mmol/l are with low phenylalanine diet to prevent usually regarded as benign HPA and are not mental retardation, but show differences considered an indication for dietary treatment. in serum phenylalanine levels and in The wide spectrum of HPAs has led to dif- tolerance to this amino acid. Maternal ferent designations for these conditions in dif- PKU is a syndrome of congenital anomal- ferent studies. ies and mental retardation that appears in In Israel, a pioneer in establishing a national offspring of PKU mothers as a result of screening programme for HPA,3 two variants fetal exposure to the high phenylalanine of PKU have been noted, which are clinically level in the maternal blood. We studied a indistinguishable in the untreated state: severe family in which two children with severe, classical PKU with serum phenylalanine levels classical PKU and their unaffected of 1-2 to 48 mmol/I on a normal diet and brother showed mild signs of maternal phenylalanine tolerance of 200 to 500 mg/day, PKU. Their mother had no clinical signs and atypical PKU with serum phenylalanine of of PKU, but the phenylalanine concentra- 1-2 to 2 4 mmol/I and a 500 to 1200 mg/day treatment is tion in her serum reached a level that tolerance. Less stringent dietary http://jmg.bmj.com/ usually characterises PKU patients. This required in atypical PKU. (Previous commu- woman represents a rare phenotype, nications referred to these variants of PKU as 'hidden' PKU 'North European' and 'Mediterranean',45 ref- Department of benign atypical PKU. Such Human Genetics, in women may lead to maternal PKU in lecting the lack of common nomenclature.) Sackler School of the offspring, similar to overt PKU. Benign HPA (also termed 'non-PKU HPA'4) Medicine, Tel Aviv Special attention should therefore be paid was classified in this population as 'high' or University, Ramat to women having children with any of the 'low', with serum phenylalanine levels of 0-6 to

Aviv 69978, Israel. on September 25, 2021 by guest. Protected copyright. S Kleiman clinical hallmarks of maternal PKU, and 1-08 and 0-24 to 0-72 mmol/l and phenylal- L Vanagaite to children born to women known to have anine tolerance of 1100 to 1700 and 1500 to J Bernstein Y Shiloh benign HPA. The mother was also found 2000 mg/day, respectively. to be homozygous for a missense muta- HPA variability reflects a wide spectrum of Child Development tion at the phenylalanine hydroxylase mutations at the PAH locus that reduce the Institute, Sheba to different extents. Over 30 Medical Centre, Tel locus, R261Q, which does not abolish en- enzyme activity Hashomer, Israel. zymatic activity completely. In two other such mutations have been identified since the G Schwartz families, homozygosity for this mutation cloning of the PAH gene, and the correspond- N Brand resulted in atypical PKU in four children. ing enzymatic defects have been correlated A Elitzur This observation suggests that mutations with the clinical-biochemical phenotypes asso- Howard Hughes that do not completely destroy phenylala- ciated with these mutations.67 The search for Medical Institute, nine hydroxylase activity may exhibit new mutations and the finding of known muta- Department of Cell their Biology and Institute variable phenotypic expression which is tions in patients is facilitated by associ- of Molecular Genetics, unpredictable. Compound heterozygosity ation with specific haplotypes of restriction Baylor College of for R261Q and other mutations led in fragment length polymorphisms (RFLPs) in Medicine, Houston, the last 25 Texas 77030, USA. other patients either to classical PKU or the PAH gene."' During years, S L C Woo to mild benign HPA. routine screening of newborns for HPA and Genet dietary treatment of PKU patients throughout Correspondence to (J7 Med 1993;30:284-8) Dr Shiloh, Howard Hughes childhood has resulted in increasing numbers Medical Institute Research level above of such patients who grow up and lead normal Laboratories, University of A raised serum phenylalanine Michigan Medical Center, 0 12 mmol/l is defined as hyperphenylalani- lives as adults without dietary restrictions. MSRB II, Room 4570, 1150 from of This success has been overshadowed, how- W Medical Center Drive, naemia (HPA), and results impairment Ann Arbor, Michigan phenylalanine hydroxylation to tyrosine in the ever, by the recent emergence of a new syn- 48109-0650, USA. liver.'2 The defective enzyme in more than drome, maternal PKU, in women's children Received 5 August 1992. exposed in utero to high phenylalanine levels Revised version accepted 98% of cases is phenylalanine hydroxylase 13 October 1992. (PAH), and the rest are explained by defects in in their mother's blood. Maternal PKU is Phenylketonuria: variable phenotypic outcomes of the R261Q mutation and maternal PKU in the offspring of a healthy homozygote 285

characterised by low birth weight, microce- tion, are healthy, and have no history of PKU phaly, mental retardation, and a high risk of or any other metabolic or in cardiac anomalies.'2'3 It can be avoided by their families. Both in middle class

grew up J Med Genet: first published as 10.1136/jmg.30.4.284 on 1 April 1993. Downloaded from reinstating the low phenylalanine diet before families with normal nutrition typical of this conception and throughout pregnancy.'4 The community. Physical examination showed all growing awareness of the consequences of three children to be microcephalic (head cir- HPA during pregnancy has directed attention cumference below the 2nd centile). The IQ of to females with benign HPA where high HPA the boy not affected with PKU (II-2) was 89, not sufficient to cause overt PKU in the while that of his parents was 100. Since these mother might nevertheless affect her fetus."-5'7 signs could be compatible with mild maternal Superti-Furga et all8 recently described a PKU, serum phenylalanine level was tested in family in which mild PKU in two sisters the mother and found to be 1-2 mmol-l. The resulted in maternal PKU in their offspring. high level was unusual, since most people with Both sisters were homozygous for a missense this degree of HPA are usually affected with mutation (R261Q) at codon 261 of the PAH PKU and show various degrees of mental gene, which does not totally abolish PAH retardation if not treated by diet. This woman enzymatic activity. was found, however, to be well adjusted We present here genetic and molecular ana- socially and works as a school teacher. Her lyses of a family in which PKU and maternal phenylalanine tolerance was 600 mg/day. We PKU coexist in the offspring. The molecular therefore assigned a specific phenotype to this basis for maternal PKU in this family is benign woman, benign atypical PKU. We concluded atypical PKU in the mother, who is homozy- that the signs of mild maternal PKU found in gous for the R261Q mutation. Other pheno- the children resulted from maternal HPA. types associated with this mutation in the Haplotype analysis showed the children Israeli population are presented. with classical PKU in this family to be com- pound heterozygotes with mutant haplotypes 1 and 4,20 while the mother was homozygous for Patients and families haplotype 1 (fig 1). The patients were tested Newborn screening in Israel and the criteria for the presence of the following mutations for classification of the different HPAs have previously found to be associated with haplo- been previously described.'-5 Psychological types 1 and 4 in other populations: R158Q, and developmental assessment of PKU R243ter, R252W, R261 Q, E280K, P281 L, patients is done on a yearly basis between the R408W, and Y414C.6921-25 Both patients were ages of 1 and 18 years using a variety of tests found to carry the missense mutation R261Q that examine IQ, motor-graphic ability, adap- on one of their PAH . This mutation tation, educational achievement, and emotion- changes an arginine residue into glutamine at al development. The families investigated are codon 261 of the PAH results gene and in http://jmg.bmj.com/ part of a cohort of 110 Israeli families with residual enzyme activity of 30%.21-23 25 None of HPA that recently underwent genetic and mo- the other mutations was found in these lecular analysis (Kleiman et al, in preparation). patients. The presence of the R261Q mutation can be detected by PCR and subsequent Hinfl digestion. Further investigation of the segre- Methods gation of this mutation in the family showed, For the molecular analysis, construction of unexpectedly, that the mother was homozy- RFLP haplotypes at the PAH gene and detec- gous for this defect (fig 2). Direct sequencing on September 25, 2021 by guest. Protected copyright. tion of previously recognised point mutations of PCR products (not shown) confirmed the were as previously described.419 homozygosity of this woman for R261Q. The father's mutation is still unknown. Results GENETIC-MOLECULAR ANALYSIS OF A FAMILY WITH PKU AND MATERNAL PKU In the family presented in fig 1, two of the 11 2 children are affected with classical PKU and are treated with a low phenylalanine diet. The parents are both of Palestinian Arab extrac- 2 3 2 3 :rs I bp

°-O 2 - 193 4/12 1/1 84-l -84

Figure 2 Detection of the R261Q mutation using 11 restriction endonuclease digestion of amplified exon 7 of 2 3 the PAH gene. The mutation eliminates a HinfI site 4/1 12/1 4/1 that divides the amplifiedfragment (193 bp) into two portions of 109 and 84 bp. Lane 1: undigested PCR Figure 1 Pedigree of the family with PKU and product. Lane 2: PCR product of an R261Q maternal PKU. Numbers denote PAH haplotypes homozygote, digested with HinfI. Lane 3: digested according to Woo.20 product from a normal homozygote. 286 Kleiman, Vanagaite, Bernstein, Schwartz, Brand, Elitzur, Woo, Shiloh

VARIABLE PHENOTYPES ASSOCIATED WITH THE severity of maternal PKU in the offspring has R261Q MUTATION also been noted by others.2829 It is noteworthy In order to assess the involvement of the that the two PKU children in our family and J Med Genet: first published as 10.1136/jmg.30.4.284 on 1 April 1993. Downloaded from R261Q mutation in HPA in the Israeli popula- their unaffected brother exhibited the same tion, the entire cohort of 110 HPA families signs of maternal PKU, similar to the family (Kleiman et al, in preparation) was screened reported by Levy et al.27 These findings indic- for the presence of this defect using PCR with ate that phenylalanine hydroxylase activity in Hinfl digestion and sequencing in cases posit- the normal fetus did not protect him against ive for this test. The mutation was detected in the excess phenylalanine in the maternal another five Palestinian Arab and Jewish fami- blood. lies with different HPAs (table). It is note- These observations indicate the possibility worthy that in two Palestinian families, homo- of mild cases of maternal PKU, primarily zygosity for R261Q resulted in the atypical microcephaly, might be a sign to the paediatri- variant of PKU requiring dietary treatment. cian to examine serum phenylalanine in the Compound heterozygosity for R261Q and mother. A finding of maternal HPA would other mutations led either to classical PKU or imply a high risk for recurrence of this syn- to benign HPA. The R261Q mutation was drome in subsequent offspring, and hence the associated with haplotype 1 in all but one necessity of dietary treatment during each family (table). pregnancy. Moreover, pregnancy outcomes should be systematically followed up in women previously diagnosed as having benign Discussion HPA. Similar concerns were recently The term HPA covers a broad spectrum of expressed by other investigators.'529 phenotypes differently designated in various The molecular basis of benign HPA in our studies. The mother in the family studied here family is of particular interest. The R261Q exhibits a rare phenotype, with a phenylala- mutation has been previously identified in nine level characteristic of PKU patients but PKU patients, 21 22bubut seems to be variably with normal intelligence without dietary treat- expressed. We identified in our population two ment. Subjects with high, untreated HPA and phenotypic outcomes of homozygosity for this normal development have occasionally been mutation: atypical PKU which should be noted in the past.'26 While this phenotype treated with diet to prevent mental retard- indicates the ability of the central nervous ation, and benign atypical PKU with normal system to cope with high HPA under certain intelligence under a normal diet. The sisters undefined circumstances, the maternal PKU with high HPA and children affected with in our patient's children shows that the off- maternal PKU reported by Superti-Furga et spring of such subjects do not always escape all8 were also homozygous for the R261 Q mu-

the harmful effect of high maternal HPA. tation, with somewhat more pronounced phe- http://jmg.bmj.com/ The coexistence of classical PKU and notypic effects and more grave consequences maternal PKU in the same subjects was noted in the children. Okano et aP3 recently showed recently by Levy et aF7 in a family in which the that in European populations subjects homo- mother had overt, untreated, classical PKU. zygous for R261Q exhibit a condition which, The maternal PKU in our family is less severe, in our nomenclature, falls into the category of however, than that usually observed in chil- high benign HPA. This variable phenotypic to mothers.'21' In the expression might be the result of interaction dren born PKU family on September 25, 2021 by guest. Protected copyright. described by Superti-Furga et al,'8 the two with genetic and physiological factors of sisters had serum phenylalanine levels of 1 26 unknown nature. DiSilvestre et aP0 described and 1-34 mmol/l, low-normal intelligence, and clinical differences between sibs with identical more severe maternal PKU in their children PAH haplotypes; although serum phenylala- than was seen in our patients. This correlation nine and phenylalanine tolerance were identi- between the extent of maternal HPA and the cal, PKU appeared in one sib and benign HPA

Association of the R261Q mutation with different HPAs. Mutant Serum Phenylalanine PAH PAH Ethnic origin phenylalanine tolerance Phenotypic Patient haplotypes mutations of R261Q (mmol/l)* (mg/day) classificationt R261Q homozygotes FA$ 1/1 R261Q/R261Q Palestinian-Arab 1 2 600 Benign atypical PKU MW sibs 1/1 R261Q/R261Q Palestinian-Arab 1-7 700 Atypical PKU VW 1/1 R261Q/R261Q Palestinian-Arab 1-8 800 Atypical PKU SS i 1/1 R261Q/R261Q Palestinian-Arab 1-6 600 Atypical PKU AS 1/1 R261Q/R261Q Palestinian-Arab 19 600 Atypical PKU R261Q compound heterozygotes CL 1/2 R261Q/R408W Jewish-Iraqi 2 5 300 Classical PKU MA§ 1/4 R261Q/? Palestinian-Arab 2-2 400 Classical PKU HAIl 1/4 R261QJ? Palestinian-Arab 1-9 400 Classical PKU NH 1/1 R261Q/? Palestinian-Arab 2-5 350 Classical PKU YH sibs 1/1 R261Q/? Jewish-Iraqi 1-56 350 Classical PKU ZH 1/1 R261Q/? Jewish-Iraqi 1-38 350 Classical PKU OF 28/10 R261Q/? Jewish-Iraqi 1-8 300 Classical PKU KH¶ 1/1 R261Q/? Jewish-Iraqi 0-48 1600 Mild benign HPA MH** 1/1 R261Q1? Jewish-Iraqi 0 51 1700 Mild benign HPA * Under normal diet. t See Avigad et al.4 In that paper classical PKU was termed 'the North European variant', atypical PKU was designated 'the Mediterranean variant', and benign HPA was termed 'non-PKU HPA'. t I 2 in fig 1. § II in fig 1. 1II-3 in fig 1. ¶ Mother of YH and ZH. ** Brother of KH. Phenylketonuria: variable phenotypic outcomes of the R261Q mutation and maternal PKU in the offspring of a healthy homozygote 287

in the other. The mutations responsible for operation. S L C Woo is an investigator at the these phenotypes were not reported. The phe- Howard Hughes Medical Institute. This study associated with was the United States-Israel notypic variability certain supported by J Med Genet: first published as 10.1136/jmg.30.4.284 on 1 April 1993. Downloaded from PAH mutations is expected to present some Binational Science Foundation. difficulty when prenatal diagnosis of PKU is based on the identification of such mutations. 1 Scriver CR, Kaufmnan S, Woo SLC. The hyperphenyl- alaninemias. In: Scriver CR, Beaudet AL, Sly WS, Valle The variety of phenotypes associated with D, eds. The metabolic basis ofinherited disease. 6th ed. New for and York: McGraw-Hill, 1989:495-546. compound heterozygosity R261Q 2 Guttler F, Lou H. Phenylketonuria and hyperphenylalani- other mutations (table) has been noted by nemia. In: Fernandes J, Saudubray JM, Tada K, eds. and is not in view of Inborn metabolic diseases - diagnosis and treatment. Berlin: others,'021-232531 surprising Springer, 1990:161-74. the fact that it leaves a residual enzymatic 3 Cohen BE, Szeinberg A, Levine T, et al. Phenylketonuria in activity of 30%.2 However, even subjects with Israel. Monogr Hum Genet 1978;9:95-101. 4 Avigad S, Kleiman S, Weinstein M, et al. Compound similar genotypes can show different pheno- heterozygosity in non-PKU hyperphenylalaninemia: the types. Two with the contribution of mutations for classical PKU. Am J Hum patients R261Q/R408W Genet 1991;48:393-9. genotype reported by Okano et aP3 had serum 5 Shiloh Y, Avigad S, Kleiman S, et al. Molecular analysis of phenylalanine levels of 1 26 and 102 mmol/l hyperphenylalaninemia in Israel: a study of Jewish gen- etic diversity. In: Bonne-Tamir B, Adam A, eds. Genetic under normal diet, compared to 2-5 mmol/l in diversity among Jews: diseases and markers at the DNA our patient with this genotype (table). Since level. Oxford: Oxford University Press, 1992:237-47. 6 Eisensmith RC, Woo SLC. Phenylketonuria and the the R408W mutation completely abolishes phenylalanine hydroxylase gene. Mol Biol Med 1991;8:3- PAH activity, a residual enzymatic activity of 18. 7 Konecki DS, Lichter-Konecki U. The phenylketonuria 15% is expected in such a compound heterozy- locus: current knowledge about alleles and mutations of gote. We would have expected high benign the phenylalanine hydroxylase gene in various popula- tions. Hum Genet 1991;87:377-88. HPA or atypical PKU in such patients, but our 8 John SWM, Rozen R, Scriver CR, Laframbroise R, patient shows classical PKU. Indeed, Okano et Laberge C. Recurrent mutation, gene conversion, or out recombination at the human phenylalanine hydroxylase aP3 noted that of nine patients with locus: evidence in French-Canadians and a catalog of expected residual PAH activity of 15%, four mutations. Am J Hum Genet 1990;46:970-4. a 9 Berthelon M, Caillaud C, Rey F, et al. Spectrum of phenyl- showed mild variant of PKU and five had ketonuria mutations in Western Europe and North classical PKU. These observations underline Africa, and their relation to polymorphic DNA haplo- types at the phenylalanine hydroxylase locus. Hum Genet the importance of as yet undefined genetic and 1991; 86:355-8. physiological factors affecting the final pheno- 10 Dianzani I, Forrest SM, Camaschella C, Saglio G, Ponzone outcome in A, Cotton HG. Screening for mutations in the phenylala- typic PAH deficiencies. nine hydroxylase gene from patients with phenylketo- It is noteworthy that in one of the Jewish- nuria by using the chemical cleavage method: a new splice both classical PKU and mild mutation. AmJ Hum Genet 1991;48:631-5. Iraqi families, 11 Svensson E, von Dobeln U, Hagenfeldt L. Polymorphic benign HPA were associated with the R261Q DNA haplotypes at the phenylalanine hydroxylase locus mutation in different and their relation to phenotype in Swedish phenylketo- subjects (see YH, ZH, nuria families. Hum Genet 1991;87:11-17. KH, and MH, table). We assume that the 12 Levy HL. Maternal phenylketonuria. Prog Clin Biol Res mutations associated with the other PAH 1988;281 :227-42. 13 Rouse B, Lockhart L, Matalon R, et al. Maternal phenyl- http://jmg.bmj.com/ in each of these phenotypes are different: a ketonuria pregnancy outcome: a preliminary report of classical PKU mutation in the affec- facial dysmorphology and major malformations. J Inher severely Metab Dis 1990;13:289-91. ted subjects, and a mutation with a milder 14 Smith I, Glossop J, Beasley M. Fetal damage due to effect on the enzyme in those affected with maternal phenylketonuria: effects of dietary treatment and maternal phenylalanine concentrations around the benign HPA. This genetic model for benign time of conception (an interim report from the UK HPA has been discussed in a pre- Phenylketonuria Register). J Inher Metab Dis 1990; extensively 13:651-7. vious communication from our laboratory.4 15 Luder ASW, Greene CL. Maternal phenylketonuria and Haplotype 1 is associated with 50% of the hyperphenylalaninemia: implications for medical practice on September 25, 2021 by guest. Protected copyright. in the United States. AmJ Obstet Gynecol 1989;161:1102- mutant PAH alleles among Palestinian Arabs 5. (Kleiman et al, in preparation). In this com- 16 Hanley WB, Clarke TR, Schoonheyt WE. Undiagnosed phenylketonuria in adult women: a hidden public health munity eight of 36 mutant alleles with this problem. Can Med Assoc 71990;143:513-6. haplotype carry the R261Q mutation, which is 17 Waisbren SE, Levy HL. Effects of untreated maternal hyperphenylalanemia on the fetus: further study of fami- also usually associated with this haplotype lies identified by routine cord blood screening. J7 Pediatr in European and Mediterranean popula- 1990;1 16:926-9. 18 Superti-Furga A, Steinmann B, Duc G, Gitzelman R. tions.6791021-23 Interestingly, a similar PAH Maternal phenylketonuria syndrome in cousins caused by allele bearing the same mutation and haplotype mild, unrecognized phenylketonuria in their mothers was homozygous for the phenylalanine hydroxylase arg- found in five Jewish families of Iraqi 261 -gln-261 mutation. Eur J Pediatr 1991;150:493-7. origin. In another family from the same com- 19 Weinstein M, Eisensmith RC, Abadie V, et al A missense mutation, S349P, completely inactivates phenylalanine munity, R261 Q was associated with haplotype hydroxylase and is involved in different hyperphenylala- 28 (table). A rare association of this mutation ninemias in North African Jews. Hum Genet (in press). with P4 20 Woo SLC. Collation of RFLP haplotypes at the human haplotype 28 was noted by Tyfield et a phenylalanine hydroxylase (PAH) locus. Am3'Hum Genet in south west England. The site of this muta- 1989;43:781-3. tion involves a 21 Abadie V, Lyonnet S, Maurin N, et al. CpG dinucleotides CpG dinucleotide, a known hot are mutation hot spots in phenylketonuria. Genomics spot for sequence variation, making the recur- 1989;5:936-9. rence of this mutation832 a 22 Okano Y, Wang T, Eisensmith RC, Steinmann B, Gitzel- possibility. How- mann R, Woo SLC. Missense mutations associated with ever, gene flow between different populations RFLP haplotypes I and 4 of the human phenylalanine cannot be ruled out. We to hydroxylase gene. Am J Hum Genet 1990;46:18-25. hope resolve this 23 Okano Y, Eisensmith RC, Guttler F, et al. Molecular basis question using additional sequence variations of phenotypic heterogeneity in PKU. N Engl J Med at the PAH locus. 1991;324:1232-8. 24 Tyfield LA, Osbom MJ, Holton JB. Molecular hetero- geneity at the phenylalanine hydroxylase locus in the population of the South-west of England. J Med Genet We thank the staff of the Institute for Child 1991;28:244-7. at the Sheba Mecical 25 Okano Y, Wang T, Eisensmith RC, et al. Phenylketonuria Development Centre and missense mutations in the Mediterranean. Genomics the patients and their families for their co- 1991,9:96-103. 288 Kleiman, Vanagaite, Bernstein, Schwartz, Brand, Elitzur, Woo, Shiloh

26 Primrose DA. Phenylketonuria with normal intelligence. 30 DiSilvestre D, Koch R, Groffen J. Different clinical mani- Ment Defic Res 1983;27:239-41. festations of hyperphenylalaninemia in three siblings with 27 Levy HL, Lobbregt D, Sansaricq C, Snyderman SE. Com- identical phenylalanine hydroxylase genes. Am Hum parison of phenylketonuric and nonphenylketonuric sib- Genet 1991;48:1014-6. lings from untreated preganancies in a mother with 31 Tyfield LA, Meredith AL, Osborn MJ, et al. Genetic J Med Genet: first published as 10.1136/jmg.30.4.284 on 1 April 1993. Downloaded from phenylketonuria. Am Hum Genet 1992;44:439-42. analysis of treated and untreated phenylketonuria in one 28 Levy HL, Waisbren SE. Effects of untreated maternal family. Med Genet 1990;27:564-8. phenylketonuria and hyperphenylalaninemia on the fetus. 32 Okano Y, Wang T, Eisensmith RC, Guttler F, Woo SLC. N EnglJ7 Med 1983;309:1269-74. Recurrent mutation in the human phenylalanine hydrox- 29 Hanley WB, Clarke JTR, Schoonkeyt W. Maternal phenyl- ylase gene. AmJ_ Hum Genet 1990;46:919-24. ketonuria (PKU) - a review. Clin Biochem 1987;20:149- 58. http://jmg.bmj.com/ on September 25, 2021 by guest. Protected copyright.