Hum Genet (1993) 90:645-649 human .. genetics 9 Springer-Verlag 1993 A missense mutation, $349P, completely inactivates phenylalanine hydroxylase in North African Jews with phenylketonuria Michal Weinstein l, Randy C. Eisensmith 2, V~ronique Abadie 3, Smadar Avigad 1, Stanislas Lyonnet 3, Gerard Schwartz 4, Arnold Munnich 3, Savio L.C. Woo 2, Yosef Shiloh l t Department of Human Genetics, Sackler School of Medicine, Tel Aviv University, Ramat Aviv 69978, Israel 2Howard Hughes Medical Institute, Department of Cell Biologyand Institute of Molecular Genetics, BaylorCollege of Medicine, Houston, TX 77030, USA 3 Unit6 de Recherches sur les Handicaps G6n6tiques de L'Enfant, INSERMU. 12, H6pital des Enfants-Malades, 149, Rue de S~vres, F-75743 Paris Cedex 15, France 4Child DevelopmentInstitute, Sheba Medical Center, Tel Hashomer52621, Israel Received: 28 January 1992 Abstract. The majority of hyperphenylalaninemias (HPAs) result from mutations at the gene for phenylalanine hydroxy- lase (PAH). The broad phenotypic variability of these condi- tions, ranging from phenylketonuria (PKU) to mild benign HPA, is underlain by a wide spectrum of mutations giving rise to various genotypic combinations. Mutant PAH alleles, labeled by specific polymorphic haplotypes and mutations, are becoming useful markers in human population genetics. We report here a mutant PAH allele found in Jews from Mo- rocco and Tunisia, marked by haplotype 4 and a missense mutation, TCASer---~CCA Pr~ at codon 349 in exon 10 of the gene. In vitro expression of the mutation showed normal lev- els of mRNA with virtually no enzymatic activity or protein immunoreactivity, pointing to a highly unstable protein. A homozygote for this mutation showed the most severe ("clas- sical") type of PKU, while compound heterozygotes showed two other types of HPA - "atypical" PKU and "high benign" HPA - illustrating the interplay between different mutations that gives rise to various HPAs. Introduction The hepatic enzyme phenylalanine hydroxylase (PAH) cat- alyzes the irreversible hydroxylation of the amino acid phenylalanine to tyrosine. Mutations at the PAH locus block phenylalanine metabolism and result in excessive levels of serum phenylalanine, a condition termed hyperphenylala- ninemia (HPA) (Scriver et al. 1988, 1989). A genotypic com- bination at the PAH locus that results in serum phenylalanine levels of 1.2 mM and higher is usually expressed as the auto- somal recessive phenylketonuria (PKU) featured primarily by mental retardation. A variety of less severe HPAs are be- Correspondence to: Y. Shiloh nign and do not require treatment (Scriver et al. 1989; Guttler and Lou 1990). Over 20 PAH mutations involved in these conditions have been identified, with considerable linkage disequilibrium with specific haplotypes of polymorphic restriction sites at the PAH locus (Berthelon et al. 1991; Eisensmith and Woo 1991; Konecki and Lichter-Konecki 1991). Identification of the molecular defects leading to HPAs in the Israeli popula- tion is of particular interest because of their wide phenotypic variability in this country. Two variants of PKU ("classical" and "atypical") and two types of benign HPA ("high" and "low") have been characterized in Israel during the last 27 years (see Avigad et al. 1991 for details). We have recently shown that the majority of benign HPAs in our population re- sult from compound heterozygosity for PKU alleles and other mutations that have a milder effect on the enzyme (Avi- gad et al. 1991). A second interesting aspect of HPAs in Is- rael is their ethnic background (Shiloh et al. 1991). PKU has been found in this country in Arabs and among Sephardic and Oriental Jews (Cohen et al. 1978). Since in their previous locations these Jewish communities were usually genetic iso- lates, the patients are expected to show unique mutations. For example, a single gene deletion was found to be unique for all Yemenite Jewish patients with PKU (Avigad et al. 1990). We report here a missense mutation at the PAH locus found among Jews of North African extraction. This muta- tion, $349P, completely inactivates the enzyme and is in- volved in at least three types of HPA in this community. Subjects and methods Patients and families Newborns in Israel are routinely screened for HPA: phenylalanine lev- els are estimated in a central laboratory on dried blood spots, using the