The impact of duration and control of type 1 diabetes mellitus on microvascular function is strongly modified by the gene for connexin 37

Abstract

Abstract Introduction Type 1 diabetes mellitus (T1DM) is almost inevitably accompanied by microvascular dysfunction. This could be responsible for cardiovascular events and is supposed to be caused mainly by long-term exposure to hyperglycemia. Nevertheless, relationship between duration and control of T1DM with microvascular complications can be modified by genetic factors; one of frequently discussed candidate genes is connexin37 (cx37), namely its rs1764391 (C1019>T (Pro319>Ser) polymorphism. We already observed sex specific association between cx37 polymorphism with macrovascular changes but also with retinopathy, neuropathy and diabetic foot. In the recent study, we analyzed if the impact of duration and control of T1DM on directly measured microvascular function is modified by cx37 gene polymorphism. Methods In 235 men and 227 women with T1DM (mean age 43.6 ± 13.6 years; mean duration of diabetes 22.1 ± 11.3 years) wide spectrum of clinical, laboratory and hemodynamic parameters was measured. Establishment of microvascular function measured by photoplethysmography (detection of blood volume changes in the microvasculature in lower extremities) and calculated as Oliva/Roztocil index (ORI), was analyzed. Cx37 gene polymorphism was measured by PCR-RFLP. The correlation (Pearson’s correlation coefficient) between duration of T1DM and ORI was calculated including analysis of potential modification by control of diabetes (HbA1c) and by cx37 gene polymorphism and standardized for potential confounders (sex, age, smoking, presence of hypertension, central obesity …) by multiple regression. The analysis was conducted separately for duration of T1DM below (n=256) and above (n=206) 20 years as the linear relationship between ORI and T1DM duration tends to change accordingly. Results In patients with T1DM, distribution of Cx37 genotypes did not differ from the already described populations (TT/CT/CC: 9.7/44.4/45.9%). In patients with satisfactory control of diabetes (HbA1c<53 mmol/mol; n=105) we detected worsening (increase) of ORI with duration of diabetes only in TT homozygotes and CT heterozygotes for duration of at least 20 years (r=0.6, p=0.006), while in patients with unsatisfactory control (HbA1c>60 mmol/mol;n=270), we detected worsening of ORI with duration of diabetes only in CC homozygotes, both for duration 0-20 years (r=0.35, p=0.03) and for duration of at least 20 years (r=0.47, p=0.03). Conclusion Microvascular function in satisfactory controlled T1DM was worsening with diabetes duration only in T allele carriers of Cx37 gene, the worsening was detected only for patients with duration longer than 20 years. However, if T1DM control was insufficient, microcirculation was worsening only in CC homozygotes.