Analysis of copy number variation of CYP21A2 gene and the type of CYP21A1P/CYP21A2 fused gene in patients with 21-hydroxylase deficiency

Abstract

Objective: To analyze the copy number variation of CYP21A2 gene in 21-hydroxylase deficiency (21-OHD) patients, and identify the three copy repetition, single copy deletion of CYP21A2 gene and the type and proportion of CYP21A1P/CYP21A2 fused gene in 21-OHD patients. Methods: A total of 424 patients (140 males and 284 females) with 21-OHD who visited Peking Union Medical College Hospital from January 2015 to January 2018 were enrolled and the average age was (17.1±12.4) years. All clinical and biochemical data were collected. DNAs were extracted from peripheral blood leukocytes, and CYP21A2 gene mutation and copy number variation were detected by Sanger sequencing and multiple ligation probe amplification (MLPA). Results: Of 424 21-OHD patients, 287 (67.7%) had two copies of CYP21A2 gene, 137 (32.3%) had copy number variation, of which 1 patients (0.2%) had 3 copies of CYP21A2 gene and 136 (32.1%) were carriers of large deletion/rearrangement mutation of CYP21A2 gene. Three pathogenic mutations including a truncated Q319X protein mutation were detected in the patient with 3 copies of CYP21A2 gene. Of 136 patients with large deletion/rearrangement mutation of CYP21A2 gene, 82 (60.3%) carried fused CYP21A1P/CYP21A2 gene, and the remaining 54 harbored the one allele deletion of CYP21A2. The most common types of fused CYP21A1P/CYP21A2 gene were CH-5, CH-1 and CH-2, with the frequency being 31.7% (26 cases), 26.8% (22 cases) and 19.5% (16 cases), respectively, and followed by CH-4 and CH-7, with the incidence being 8.5% (7 cases) and 4.9% (4 cases), respectively. In addition, two cases of CH-3, CH-6 and CH-8 and one case of CH-9 were detected. Conclusions: This is the first study to detect the occurrence of CYP21A2 gene copy number variation and fused CYP21A1P/CYP21A2 gene in a large cohort of 21-OHD patients. The number of CYP21A2 gene copies in 21-OHD patients includes 2 copies, 1 copy deletion and 3 copies duplication. One copy deletion of CYP21A2 includes one allele deletion of CYP21A2 gene and fused CYP21A1P/CYP21A2 gene. In patients with 3 copies of CYP21A2 gene, pathogenic mutations should be verified in all 3 copies of CYP21A2 gene to make the precise diagnosis. Therefore, the accurate molecular diagnosis of 21-OHD patients should take both genotype and copy number variation of CYP21A2 into account.