Objective: To evaluate whether the joint risk of diabetes and atherosclerosis tracked within families, we assessed the correlation between a family history of diabetes and intimal-medial thickness (IMT) of the common carotid artery (CCA).
Research design and methods: Study subjects included 620 nondiabetic individuals from 24 families enrolled in the San Antonio Family Heart Study. The thickness of the far walls of the CCA was measured by B-mode ultrasonography. Statistical analyses included familial correlations to account for the nonindependence of family data.
Results: After adjusting for sex, age, and IMT reader effects, the heritability of IMT in this population was 16% (P = 0.009). Using a more comprehensive family history score that accounted for diabetes status of the individual's parents and older siblings, we observed a significant correlation between family history score and increased CCA IMT (0.006 mm increase in CCA IMT for every point increase of diabetes family history score, P = 0.016). This association remained even after further adjustment for BMI, smoking, and fasting insulin and glucose levels. After adjusting for several cardiovascular risk factors, the mean CCA IMT in those with high family history scores for diabetes was still 0.037 mm thicker than those with low family history scores for diabetes (P = 0.040).
Conclusions: These results suggest that the genetic contribution to CCA IMT variability is modest. Also, the small increase in subclinical atherosclerosis observed even among nondiabetic Mexican Americans with a positive family history of diabetes is probably transmitted along with the risk of diabetes through shared etiologic risk factors between diabetes and cardiovascular disease.