Abstract: Objective To investigate the relationship between gene polymorphisms of homocysteine (Hcy), metabolic enzymes methylenetetrahydrofolate reductase MTHFR C677T and chronic pulmonary heart disease (CPHD). Methods The gene polymorphisms of MTHFR C677T were determined by the polymerase chain reaction- restriction fragment length polymorphism（PCR-RFLP） in CPHD patients (n=120) and healthy control (HC, n=120), and genotyping was carried on. The automatic biochemistry analyzer was used to detect the level of Hcy and other related biochemical indicators. Results There was significant difference in Hcy level between the CPHD group and HC group (P＜0.05). The mutation frequencies of CC, CT and TT were 24.17%, 43.33% and 32.50%, 35.00%, 47.50% and 17.50% in the CPHD group and HC group. The mutation frequencies of allele C /T were 45.83% and 54.17% in HC group, and 58.75% and 41.25% in control group. There was significant difference in the overall frequency distribution between the three genotypes (χ2 =8.010, P＜0.05). The frequency of T allele was significantly higher in CPHD group than that in control group (χ2=8.025， P＜0.05). Conclusion The increased Hcy and its metabolic enzyme MTHFR C677T may be involved in the occurrence and development of CPHD.

Key words: homocysteine, 5,10- methylenetetrahydrofolate reductase (FADH2), polymorphism, genetic, gene expression, pulmonary heart disease, MTHFR C677T