PIK3CA and microscopic polyangiitis: The mutations of rs1607237 in the PIK3CA gene had a lower incidence of MPA with the CT genotype in the codominant model (CT versus CC, OR = 0.47, 95% CI [0.30–0.73], and p = 0.0039), the dominant model (CT/TT versus CC, OR = 0.55, 95% CI [0.37–0.82], and p = 0.0031), and the overdominant model (CT versus CC/TT, OR = 0.49, 95% CI [0.32–0.76], and p = 0.0013).