Relation between HLA and copy number variation of steroid 21-hydroxylase in a Swedish cohort of patients with autoimmune Addison's disease.

Abstract

Autoantibodies against the adrenal enzyme 21-hydroxylase is a hallmark manifestation in autoimmune Addison's disease (AAD). Steroid 21-hydroxylase is encoded by CYP21A2, which is located in the HLA region together with the highly similar pseudogene CYP21A1P. A high level of copy number variation is seen for the two genes, and therefore we asked if genetic variation of the CYP21 genes is associated with AAD. Using next-generation DNA sequencing, we estimated the copy number of CYP21A2 and CYP21A1P together with HLA alleles in 479 Swedish patients with AAD and autoantibodies against 21-hydroxylase, and in 1,393 healthy controls. With 95% of individuals carrying two functional 21-hydroxylase genes, no difference in CYP21A2 copy number was found when comparing patients and controls. In contrast, we discovered a lower copy number of the pseudogene CYP21A1P among AAD patients (p = 5 x 10-44) together with associations of additional nucleotide variants in the CYP21 region. However, the strongest association was found for HLA-DQB1*02:01 (p = 9 x 10-63), which in combination with the DRB1*04:04-DQB1*03:02 haplotype imposed the greatest risk of AAD. We identified strong associations between copy number variants in the CYP21 region and risk of AAD, although these associations most likely are due to linkage disequilibrium with disease-associated HLA class II alleles.