Subgroup and correlation analyses and of ERAP1methylation
ERAP1 was known to play roles cooperated with HLA-B27 in AS.
Nevertheless, we found that the methylation levels of ERAP1_1 and
ERAP1_2 islands of HLA-B27 positive patients were not significantly
different from HLA-B27 negative patients (Z = -0.180, P =
0.857). The known environmental factors associated with DNA methylation
of smoking (Z = -0.268, P = 0.789) and alcohol use
(Z = -0.969, P = 0.332) were also reported not associated
with the methylation level in AS patients detailed in Table 4. Among the
demographic and clinical factors, we found that patients with family
history have lower methylation level of ERAP1_1 island (Z =
-2.258, P = 0.024). Non-steroidal anti-inflammatory drugs
(NSAIDs) use was significantly associated with higher methylation level
of ERA1_2 island (Z = -2.113, P = 0.035), but not any
medication use history (Z = -0.605, P = 0.545). As to the
variates about disease activity and function, we also found that the
methylation level of ERAP1_1 island was significant associated with
global back pain (rs = 0.502, P = 0.002) of AS
patiens. X-ray classification of sacroiliac joint (rs =
0.548, P = 0.018) was associated with the methylation level of
ERAP1_2 island (Table 5).