Conclusions
Parallel with HLA-B27, MICA confers strong susceptibility to AS in US white and Han Chinese populations.
Methods
We examined 1543 AS patients and 1539 controls from two ethnic populations by sequencing MICA and genotyping HLA-B alleles. Initially, 1070 AS patients and 1003 controls of European ancestry were used as a discovery cohort, followed by a confirmation cohort of 473 Han Chinese AS patients and 536 controls. We performed a stratified analysis based on HLA-B27 carrier status. We also conducted logistic regression with a formal interaction term.
Objective
The human major histocompatibility complex class I chain-related gene A (MICA) controls the immune process by balancing activities of natural killer cells, γδ T cells and αβ CD8 T cells, and immunosuppressive CD4 T cells. MICA is located near HLA-B on chromosome 6. Recent genomewide association studies indicate that genes most strongly linked to ankylosing spondylitis (AS) susceptibility come from the region containing HLA-B and MICA. While HLA-B27 is a well-known risk genetic marker for AS, the potential effect of linkage disequilibrium (LD) shields any associations of genes around HLA-B with AS. The aim of this study was to investigate a novel independent genetic association of MICA to AS.
Results
Sequencing of MICA identified that MICA*007:01 is a significant risk allele for AS in both Caucasian and Han Chinese populations, and that MICA*019 is a major risk allele in Chinese AS patients. Conditional analysis of MICA alleles on HLA-B27 that unshielded LD effect confirmed associations of the MICA alleles with AS. Conclusions: Parallel with HLA-B27, MICA confers strong susceptibility to AS in US white and Han Chinese populations.