Two mutations within the coding sequence of the phenylalanine hydroxylase gene

Area of Science:

• Biochemistry
• Genetics
• Molecular Biology

Background:

• Phenylketonuria (PKU) and hyperphenylalaninemia are genetic disorders caused by mutations in the phenylalanine hydroxylase (PAH) gene.
• Understanding genotype-phenotype correlations is crucial for diagnosing and managing these conditions.

Purpose of the Study:

• To identify and characterize novel mutations in the PAH gene.
• To investigate the impact of these mutations on phenylalanine hydroxylase enzyme activity and phenylalanine tolerance.

Main Methods:

• Restriction fragment analysis to detect mutations.
• Polymerase chain reaction (PCR) amplification of specific gene exons.
• Direct DNA sequencing to confirm mutation type and location.
• Analysis of patient genotypes and phenotypes.

Main Results:

• Two previously unidentified PAH mutations were discovered: one affecting exon 7 (BamHI site) and another affecting exon 11 (HindIII site).
• The exon 7 mutation involves a G/C to T/A transversion, creating a premature stop codon and leading to a truncated protein.
• The exon 11 mutation results in the deletion of a leucine codon in the enzyme's catalytic region.
• A patient with classical phenylketonuria was found to be a compound heterozygote for these two mutations.

Conclusions:

• Each identified mutation causes a significant loss of phenylalanine hydroxylase enzymatic activity.
• These novel mutations contribute to the spectrum of phenylketonuria and hyperphenylalaninemia.
• The findings support the role of multiple PAH gene mutations in explaining variable phenylalanine tolerance in patients.