ObjectiveTo investigate the association between homocysteine (Hcy) and the C677T gene polymorphism in its key metabolic enzyme, methylenetetrahydrofolate reductase (MTHFR), and the complications of hypertension, type 2 diabetes mellitus and atherosclerosis in patients with obstructive sleep apnea hypopnea syndrome (OSAHS).MethodsA total of 85 OSAHS patients and 77 non-OSAHS patients were enrolled. The genotypes, and levels of serum Hcy, fasting blood glucose and hemoglobin Alc of all subjects were detected, while cervical vascular ultrasound was performed simultaneously. Hcy ≥10μmol/L was defined as hyperhomocysteinemia(HHcy). The serum Hcy levels were compared among patients with different genotypes. The Hcy levels, MTHFR C677T gene polymorphism, and C/T allele frequencies were compared among an OSAHS with complications group, a pure OSAHS group, and a control group (without OSAHS or complications). Then, multivariate binary Logistic regression analysis was performed to identify independent risk factors for complications in OSAHS patients with confounding factors adjusted.ResultsThe Hcy levels in the patients with CC, CT and TT genotypes were 10.11(9.15, 11.07), 10.86 (9.58, 11.10) and 15.81 (11.43, 50.76) μmol/L, respectively. Hcy level in the patients with TT genotype was significantly higher than that in the cases with CT or CC genotypes (both P< 0.05). The Hcy levels of the OSAHS with complications group, the pure OSAHS group, and the control group were 11.16(10.05, 13.80), 9.88 (9.31, 11.41), and 10.38(9.29, 11.34) μmol/L, respectively. The Hcy level of the OSAHS with complications group was significantly higher than that of the pure OSAHS group (P< 0.05). There were no statistically significant differences in gene polymorphism or C/T allele frequency among the three groups. After adjusting for confounding factors, it revealed that HHcy was an independent risk factor for concurrent complications in OSAHS patients, and the odds ratio (95% confidence interval) was 4.682 (1.261-17.380).ConclusionThe MTHFR C677T gene polymorphism affects serum Hcy level. HHcy is an independent risk factor for concurrent complications in OSAHS patients, however, neither the MTHFR C677T gene polymorphism nor the C/T allele frequency were associated with complications in OSAHS patients.