Follow-up of two newborns with c.158G>A (p.Arg53His) mutation in <italic><bold>PAH</bold></italic> gene and assessment of the site function

: To investigate the clinical significance of c.158G>A mutation.: The blood phenylalanine (Phe) was continuously monitored in 2 unrelated newborns with suspected hyperphenylalaninimia (HPA) carrying c.158G>A mutation. The cross-species conservation of the mutant amino acid was analyzed using T-Coffee. Swiss-Model software was used to construct a 3D protein structure and the impact of candidate mutations on the secondary structure of the protein product was analyzed. The population carrying rate of the p.Arg53His mutation was analyzed by literature searching. Allelic phenotype values (APV) and genotypic phenotype values (GPV) were used to predict the phenotype associated with the mutation. Two mutations of gene were detected in each newborn: c.611A>G(p.Tyr204Cys), c.158G>A(p.Arg53His) and c.1238G>C(p.Arg413Pro), c.158G>A(p.Arg53His). Two children tolerated normal diet and plasma Phe levels were within the normal range during follow-up. The mother of case 2 was homozygous with p.Arg53His mutation under the condition of long-term normal diet, and the blood Phe concentration and Phe/Tyr were all within the normal range. The mutant amino acids were not highly conserved among the 13 different species. The 3D structural model showed that p.Arg53His mutation reduced the hydrogen bond from 2 to 1 between the 53rd and 49th amino acids of PAH. The allele frequency of p.Arg53His was 0.015 08 in HPA patients and 0.001 621 in normal population, while the prevalence of p.Arg53His allele was highest in the East Asian normal population (0.013 73). The APV and GPV system predicted that the mutation was related to mild HPA(MHP) type. : The different compound heterozygous mutations of p.Arg53His lead to clinical phenotype varieties. The reduction of enzyme activity caused by the mutation of p.Arg53His is not sufficient to cause symptoms of phenylketonuria, so the mutation may be "likely benign".