CYP17A1 Pathogenic Variants in 26 Chinese Patients With 17α-Hydroxylase Deficiency by Targeted Long-Read Sequencing

Abstract

Abstract Background 17α-hydroxylase/17,20-lyase deficiency (17-OHD) is a rare subtype of congenital adrenal hyperplasia caused by homozygous or compound heterozygous pathogenic variants in the CYP17A1 gene. Purpose This study aimed to identify and characterize pathogenic variants in individuals with 17-OHD and to classify and validate the pathogenicity of novel variants. Methods Variants were identified via targeted long-read sequencing (TLRS) of the entire CYP17A1 gene in enrolled 17-OHD patients. The American College of Medical Genetics and Genomics (ACMG) guidelines were employed to assess the pathogenicity of novel variants. Minigene splicing assays were utilized to determine the impact of variants on RNA splicing. Results This study encompassed 26 patients with 17-OHD, detecting 2 trans pathogenic variants per patient using the TLRS method. A total of 20 pathogenic variants in the CYP17A1 were identified, with variant c.985_987delinsAA being the most frequent (28/52 alleles), followed by variant c.1459_1467del (4/52 alleles). Five novel variants including c.280T > C, c.470T > A, c.636_637del, c.866A > G, and c.1095del, were classified as pathogenic/likely pathogenic ones according to ACMG criteria. The minigene splicing assays revealed c.866A > G in exon 5 causes a frameshift due to a 104 base pair deletion, while c.470T > A generates 2 transcripts, with the vast majority spliced like the wild-type and a small fraction lacking 35 base pairs in the 5′ flank of exon 3. Conclusion The TLRS can determine the cis/trans orientation of 2 distant variants. Five novel pathogenic variants were reported, broadening the spectrum of the CYP17A1 pathogenic variants. The variant c.866A > G, located deep in the exon, affects gene function through mechanisms of aberrant splicing.