Molecular basis for nonphenylketonuria hyperphenylalaninemia.
Nonphenylketonuria hyperphenylalaninemia (non-PKU HPA) is defined as phenylalanine hydroxylase (PAH) deficiency with blood phenylalanine levels below 600 mumol/liter (i.e., within the therapeutic range) on a normal dietary intake. Haplotype analysis at the PAH locus was performed in 17 Danish families with non-PKU HPA, revealing compound heterozygosity in all individuals. By allele-specific oligonucleotide (ASO) probing for common PKU mutations we found 12 of 17 non-PKU HPA children with a PKU allele on one chromosome. To identify molecular lesions in the second allele, individual exons were amplified by polymerase chain reaction and screened for mutations by single-strand conformation polymorphism. Two new missense mutations were identified. Three children had inherited a G-to-A transition at codon 415 in exon 12 of the PAH gene, resulting in the substitution of asparagine for aspartate, whereas one child possessed an A-to-G transition at codon 306 in exon 9, causing the replacement of an isoleucine by a valine in the enzyme. It is further demonstrated that the identified mutations have less impact on the heterozygote's ability to hydroxylate phenylalanine to tyrosine compared to the parents carrying a PKU mutation. The combined effect on PAH activity explains the non-PKU HPA phenotype of the child. The present observations that PKU mutations in combination with other mutations result in the non-PKU HPA phenotype and that particular mutation-restriction fragment length polymorphism haplotype combinations are associated with this phenotype offer the possibility of distinguishing PKU patients from non-PKU individuals by means of molecular analysis of the hyperphenylalaninemic neonate and, consequently, of determining whether a newborn child requires dietary treatment.
John F. Kennedy Institute, Glostrup, Denmark.
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Economou-Petersen
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KF
Henriksen
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Guldberg
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Güttler
D001483:Base Sequence; D005091:Exons; D005260:Female; D006239:Haplotypes; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D008661:Metabolism, Inborn Errors / Q000235:genetics*; D008969:Molecular Sequence Data; D015345:Oligonucleotide Probes; D010375:Pedigree; D010649:Phenylalanine / Q000097:blood*; D010651:Phenylalanine Hydroxylase / Q000172:deficiency*; D010661:Phenylketonurias / Q000150:complications*; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D014443:Tyrosine / Q000097:blood
D015345:Oligonucleotide Probes; D014443:Tyrosine; D010649:Phenylalanine; D010651:Phenylalanine Hydroxylase