Background Case control studies have suggested synergism between history of parental consanguinity and risk of developing type 2 diabetes. Genetic components of fasting blood glucose (FBG) have been reported by heritability estimates and genetic association studies.

Methods In a cross-sectional study, 102 male healthy subjects were randomly selected from 13 primary health care centres in Jazan, Saudi Arabia. Each two subjects were siblings and total number of families was 51. Subjects were interviewed to construct extended pedigrees. Extended pedigrees were used to measure degree of consanguinity by calculating inbreeding coefficients (ICs). Constructed pedigrees included information about family history of type 2 diabetes. Pearson’s correlation coefficient was used to calculate correlation of FBG between siblings of each family. To account for the effect of environmental covariates such as food intake and physical activities on FBG, electronic-based questionnaires were utilised to calculate average daily calorific and level of physical activity. These questionnaires were based on questionnaires produced by the European Prospective Investigation of Cancer (EPIC). Additional modifications were applied to make the questionnaires suitable for Saudi Subjects.

Results The overall correlation of FBG between siblings was 0.317 (P = 0.04). To examine a possible effect of consanguinity, correlations were calculated in 4 steps each considering a more restricted range of consanguinity. In the first step all families with zero inbreeding coefficients were removed resulting in an increase of FBG correlation (r = 0.419 P = 0.015). Secondly, correlation was restricted to families with ICs larger than 0.04% which resulted in further increase of correlation (r = 0.584 P = 0.003). The third step involved restricting correlation to families with ICs larger than 1.5% which showed similar trend (r = 0.699 P = 0.001). Finally, correlation was calculated in families with ICs larger than 3% (r = 0.711 P = 0.009). The effect of ICs on correlation FBG was adjusted for the difference in age, caloric intake and physical activity between siblings of each family.

Conclusion There is an observed trend of increase in correlation of FBG of siblings with increased level of consanguinity. After accounting for the effect of age and environmental variations between siblings, this trend might indicate that there is a strong genetic influence on FBG correlation and this genetic effect is augmented by degree of parental consanguinity.