Molecular basis for nonphenylketonuria hyperphenylalaninemia.

Area of Science:

• Biochemistry
• Genetics
• Metabolic Disorders

Background:

• Nonphenylketonuria hyperphenylalaninemia (non-PKU HPA) is characterized by elevated blood phenylalanine levels below 600 µmol/liter on a normal diet.
• It stems from phenylalanine hydroxylase (PAH) deficiency, presenting a diagnostic challenge compared to classic phenylketonuria (PKU).

Purpose of the Study:

• To investigate the molecular basis of non-PKU HPA in Danish families.
• To identify specific mutations in the PAH gene contributing to the non-PKU HPA phenotype.
• To differentiate non-PKU HPA from PKU through molecular analysis for appropriate newborn screening and management.

Main Methods:

• Haplotype analysis of the PAH locus in 17 Danish families.
• Allele-specific oligonucleotide (ASO) probing for known PKU mutations.
• Polymerase chain reaction (PCR) amplification and single-strand conformation polymorphism (SSCP) screening for novel mutations.

Main Results:

• Compound heterozygosity for PAH mutations was observed in all 17 families.
• Twelve families carried at least one common PKU mutation.
• Two novel missense mutations were identified: Asp415Asn and Ile306Val.
• These mutations, in combination with PKU alleles or other mutations, resulted in the non-PKU HPA phenotype.
• Specific mutation-haplotype combinations were associated with the non-PKU HPA phenotype.

Conclusions:

• The non-PKU HPA phenotype arises from the combined effect of different PAH mutations, including novel ones.
• Molecular analysis of the PAH gene and associated haplotypes can distinguish non-PKU HPA from PKU.
• This molecular approach enables early identification of neonates requiring dietary management, optimizing treatment strategies.