Evidence for genetic association of CARD9 and SNAPC4 with ankylosing spondylitis in a Chinese Han population.

OBJECTIVE: A genome-wide association study and 2 replication studies identified 2 single-nucleotide polymorphisms (SNP) of caspase recruitment domain-containing protein 9 (CARD9) and small nuclear RNA-activating complex polypeptide 4 (SNAPC4) at Chr 9q34.3 associated with ankylosing spondylitis (AS) in whites. We explored a possible association of SNP in CARD9 and SNAPC4 and AS in a Chinese Han population from Shandong.

METHODS: The study included 1150 patients with AS and 1120 healthy controls who underwent genotyping for 4 SNP of CARD9 and 2 of SNAPC4; we replicated the results in another 490 patients and 380 healthy controls of Ningxia Han Chinese during the same time. We used quantitative real-time PCR (qRT-PCR) to measure CARD9 and SNAPC4 mRNA expression in peripheral leukocytes from 44 patients and 36 controls and allele-specific mRNA expression of CARD9 and SNAPC4 in leukocytes from 130 controls.

RESULTS: We validated that an SNP in SNAPC4, rs11145835, was significantly associated with AS in our Chinese Han population (p = 0.001) and replicated the association in samples from the Chinese Ningxia Han population (p = 0.002). Carrying the G allele of rs11145835 was associated with increased risk of AS (OR 1.34, 95% CI 1.12-1.59) and with decreased expression of CARD9 (p = 0.001) and SNAPC4 (p = 0.02) in leukocytes. SNAPC4 mRNA expression was lower in leukocytes from patients than from controls (p = 0.0002).

CONCLUSION: Our study confirmed that an SNP rs11145835 in 9q34.3 that harbors CARD9 and SNAPC4 is associated with AS in a Chinese Han population, and rs11145835 in SNAPC4 is a potential causal variant.