Mutational Spectrum Of Phenylalanine Hydroxylase Gene In Ningxia Patients With Phenylketonuria

Objective Phenylketonuria is a common autosomal recessive inborn error ofamino acid metabolism and mainly results from mutations of the phenylalaninehydroxylase gene. The incidence of PKU as determined by newborn mass screeningin Chinese is1/111441, while the incidence of PKU in Ningxia is1/3065. The ratio ismuch higher than that of the national average. This may be related to the uniquegeographical location and ethnic composition of Ningxia region. Becauce economy ofNingxia is behind the average level, PKU treatment rate is relatively lower. Mostchildren are not timely diagnosis and treatment, resulting in mental retardation andhyperphenylalaninemia. In this study, we charactered the mutation distribution ofPAH gene in Ningxia, and identified the hot spots and regions and built the mutationscreening scheme, and provided base database for gene diagnoses, prenatal diagnosis,geneticis counseling.Methods The13exons and their surrounding introns of the phenylalaninehydroxylase (PAH) gene in30patients in Ningxia were directly sequenced. Multiplexligation-dependent probe amplification (MLPA) was performed for the identificationof uncharacterized mutant alleles after PAH sequence analysis of patients with PKU.Results Among60alleles,58mutant alleles (96.7%) were found. A total of23different mutations were detected, including missense (n=9), splicing (n=9), nonsense(n=2), small deletion (n=2) and large deletion (n=1). The most common mutationswere R243Q (18.3%), IVS4-1G>A (11.7%) and R111X (11.7%). Among them, twomutations (missense mutation Q304K in exon8and small deletion mutation N393delin exon11) were novel. MLPA identified a large deletion in3patients thatencompassed5’ of PAH gene and5’ of exons1(-1436_-2del) about1.4kb, one of them is homoallelic mutation, others are heteroallelic mutation. We show that thelarge deletion of the PAH gene accounts for6.7%(4/60) of all mutant PAH alleles inNingxia PKU patients.Conclusions There were obvious hotspot (R243Q, IVS4-1G>A and R111X) andhot spot areas (Exons3,5,6,7,11,12) of PAH gene in Ningxia PKU patients. Thepresent study showed that there is a large deletion mutation (-1436_-2del) in NingxiaPKU patients. The MLPA is an effective assay to detect large deletion in PAH gene.