A defective splice site at the phenylalanine hydroxylase gene in phenylketonuria and benign hyperphenylalaninemia among Palestinian Arabs

Genotype-phenotype correlations analysis of mutations in the phenylalanine hydroxylase (PAH) gene

The aims of our research were to define the genotype-phenotype correlations of mutations in the phenylalanine hydroxylase (PAH) gene that cause phenylketonuria (PKU) among the Israeli population. The mutation spectrum of the PAH gene in PKU patients in Israel is described, along with a discussion on genotype-phenotype correlations. By using polymerase chain reaction/denaturing high-performance liquid chromatography (PCR/dHPLC) and DNA sequencing, we screened all exons of the PAH gene in 180 unrelated patients with four different PKU phenotypes [classic PKU, moderate PKU, mild PKU, and mild hyperphenylalaninemia (MHP)]. In 63.2% of patient genotypes, the metabolic phenotype could be predicted, though evidence is also found for both phenotypic inconsistencies among subjects with more than one type of mutation in the PAH gene. Data analysis revealed that about 25% of patients could participate in the future in (6R)-L: -erythro-5, 6, 7, 8-tetrahydrobiopterin (BH4) treatment trials according to their mutation genotypes. This study enables us to construct a national database in Israel that will serve as a valuable tool for genetic counseling and a prognostic evaluation of future cases of PKU.

The structural basis of phenylketonuria

The human phenylalanine hydroxylase gene (PAH) (locus on human chromosome 12q24.1) contains the expressed nucleotide sequence which encodes the hepatic enzyme phenylalanine hydroxylase (PheOH). The PheOH enzyme hydroxylates the essential amino acid l-phenylalanine resulting in another amino acid, tyrosine. This is the major pathway for catabolizing dietary l-phenylalanine and accounts for approximately 75% of the disposal of this amino acid. The autosomal recessive disease phenylketonuria (PKU) is the result of a deficiency of PheOH enzymatic activity due to mutations in the PAH gene. Of the mutant alleles that cause hyperphenylalaninemia or PKU 99% map to the PAH gene. The remaining 1% maps to several genes that encode enzymes involved in the biosynthesis or regeneration of the cofactor ((6R)-l-erythro-5,6,7,8-tetrahydrobiopterin) regenerating the cofactor (tetrahydrobiopterin) necessary for the hydroxylation reaction. The recently solved crystal structures of human phenylalanine hydroxylase provide a structural scaffold for explaining the effects of some of the mutations in the PAH gene and suggest future biochemical studies that may increase our understanding of the PKU mutations.

Phenylketonuria in a low incidence population: molecular characterisation of mutations in Finland

The incidence of phenylketonuria (PKU) in Finland is extremely low, probably below 1 in 100,000. We describe the mutations and haplotypes in all four presently known patients. Mutation R408W was found on four mutant chromosomes (all haplotype 2), and IVS7nt1, R261Q, and IVS2nt1 were each found on a single chromosome. No mutation was found on the remaining chromosome. These findings support a pronounced negative founder effect as the cause of the low incidence of PKU in Finland, and are consistent with existing data regarding the European and Baltic origin of Finnish genes.