Objective: To investigate the characteristics of the phenylalanine hydroxylase (PAH) gene mutations in patients with phenylketonuria (PKU) in Tianjin and surrounding area, in order to provide basic information for genetic counseling and prenatal gene diagnosis.
Methods: All of the 13 exons and flanking introns of the PAH gene from 99 patients with PKU were amplified by polymerase chain reaction and analyzed by single strand conformation polymorphism (SSCP), denaturing high performance liquid chromatography (DHPLC) and DNA sequencing.
Results: Mutations were found in all exons or flanking introns of the PAH gene except for exons 9 and 13. A total of 41 different mutations were identified which corresponded to 93.94% (186/198) of the PAH alleles, including 22 missense mutations (53.6%), 7 nonsense mutations (17.1%), 9 splicing junction mutations(22.0%), and 3 deletion mutations (7.3%). Six novel mutations (IVS3nt+1g--> a, A165D, Q301X, G344D, P362L and R413G) were identified and another 6 mutations (S16fsdelCT, R71H, IVS5nt+1g--> a, G239S, R243X and R261X) were reported in Chinese population for the first time according to the databases from http://www.pahdb.mcgill.ca. The most common mutations included 243Q (36/198,18.18%), V399V (22/198, 11.1%), R111X (19/198, 9.6%), E6nt-96A--> g (18/198, 9.1%), R413P (15/198, 7.6%) and Y356X (13/198, 6.6%). In addition, 4 silent mutations (except V399V) in exons and 8 variations in introns were found in this study. The IVS1nt+40t--> g and IVS10nt-31g--> a were confirmed as novel variations by international PAH databases and IVS5nt-54g--> a was the first report in China.
Conclusion: The frequencies of six common mutations were close to that in Beijing area of China, but it was different in sequence. The extensive mutation spectrum of the PAH gene showed higher heterogeneity in Tianjin and surrounding areas of Northern China comparing with other reports. According to this report, exons 7 and 11 are the hot spots and should be detected first for PAH gene quick diagnosis in this area, then comes exons 3, 6 and 12, and finally exons 5, 10 and others.