Detection of Small CYP11B1 Deletions and One Founder Chimeric CYP11B2/CYP11B1 Gene in 11 beta-Hydroxylase Deficiency

Objective: 11 beta-Hydroxylase deficiency (11 beta-OHD) caused by mutations in the CYP11B1 gene is the second most common form of congenital adrenal hyperplasia. Both point mutations and genomic rearrangements of CYP11B1 are important causes of 11 beta-OHD. However, the high degree of sequence identity between CYP11B1 and its homologous gene CYP11B2, presents unique challenges for molecular diagnosis of suspected 11 beta-OHD. The aim of this study was to detect the point mutation, indel, small deletion of CYP11B1 and chimeric CYP11B2/CYP11B1 gene in a one-tube test, improving the genetic diagnosis of 11 beta-OHD. Methods: Optimized custom-designed target sequencing strategy was performed in three patients with suspected 11 beta-OHD, in which both the coverage depth of paired-end reads and the breakpoint information of split reads from sequencing data were analysed in order to detect genomic rearrangements covering CYP11B1. Long-range PCR was peformed to validate the speculated CYP11B1 rearrangements with the breakpoint-specifc primers. Results: Using the optimized target sequencing approach, we detected two intragenic/intergenic deletions of CYP11B1 and one chimeric CYP11B2/CYP11B1 gene from three suspected patients with 11 beta-OHD besides three pathogenic heterozygous point mutation/indels. Furthermore, we mapped the precise breakpoint of this chimeric CYP11B2/CYP11B1 gene located on chr8:143994517 (hg19) and confirmed it as a founder rearrangement event in the Chinese population. Conclusions: Our optimized target sequencing approach improved the genetic diagnosis of 11 beta-OHD.