A Rare Combination of Compound Heterozygous Mutations in the PAH Gene in Three Unrelated Consanguineous Iranian Families with Classical Phenylketonuria

Background: The PAH gene mutations have been linked to the development of phenylketonuria (PKU), which is recognized as the most common inborn metabolic disorder, and is caused by a deficiency in the phenylalanine hydroxylase (PAH) enzyme. The Iranian population, known for its diversity and high consanguinity, offers a valuable sample for studying autosomal recessive disorders. Our study investigated three unrelated families with PKU from Iran, utilizing clinical, laboratory, and computational approaches. Materials and Methods: We performed direct PCR sequencing for 13 exons of the PAH gene on three Iranian patients who were diagnosed with PKU. Then, Sanger sequencing confirmed the segregation of the mutations from parents to probands. Pathogenicity predictor tools, including ACMG, CADD, SIFT, Polyphen-2, and Mutation Taster, were utilized to analyze the identified genetic variants. The three-dimensional structure of the mutant forms of the protein was predicted. We also analyzed the protein-protein interactions of PAH using the STRING database. Results: All three patients exhibited rare compound heterozygosity rearrangements in the PAH gene (NM_000277.3). These included three missense variants: [c.533A>G/c.1222C>T], [c.526C>T/c.1222C>T], and [c.533A> / c.526C>T]. Conclusion: This study adds to the body of evidence establishing the association between PAH mutations and the development of PKU. We speculated that the conjunction of a high consanguinity rate in populations such as Iran, coupled with the founder effect, can give rise to atypical genetic profiles, as observed in the rearrangement of compound heterozygosity in this study Moreover, our research underscores the significance of genetic testing in the precise diagnosis of individuals affected by inborn errors of metabolism.