People with ancestral origins in the Indian subcontinent who migrate to industrialized countries are at high risk of type 2 diabetes. The relative contribution of genetic and environmental factors to this difference is not completely understood.
European origin populations with type 2 diabetes are substantially more likely to report diabetes in their mothers than in their fathers (1). This maternal excess has not been found in African-Americans (1) or Hispanics (2). Clinic-based reports have found no maternal excess in South Indians with type 2 diabetes (3), but we are not aware of any population-based data to confirm this. We used data from the Newcastle Heart Project (4) to look for an excess of maternal diabetes in U.K. South Asians.
We studied a stratified population sample of 1,509 adults aged 25–74 years, of whom 684 were of South Asian origin (259 Indian, 305 Pakistani, and 120 Bangladeshi), and 825 were of European origin. All subjects underwent an oral glucose tolerance test, and we defined diabetes and impaired glucose tolerance using the 1985 World Health Organization criteria. A family history of diabetes was based on the report of respondents.
Among Europeans, the proportion reporting maternal diabetes was higher in those with type 2 diabetes (Table 1). There was a significant excess of maternal diabetes in respondents with normal glucose tolerance and diabetes. By contrast, the proportion of South Asians reporting maternal diabetes was similar across categories of glucose tolerance. There was a significant excess of maternal diabetes among South Asians with normal glucose tolerance but not among those with diabetes. Among respondents with diabetes, mother-only diabetes was significantly more common in Europeans than in South Asians (P = 0.003), whereas father-only diabetes was not significantly different (P = 0.37).
Possible explanations for excess maternal diabetes include mitochondrial inheritance, maternal imprinting, or a detrimental effect of diabetes in pregnancy. Alternatively, the finding may reflect inaccurate reporting, better awareness of the health of mothers, longer female life expectancy, or a greater influence of mothers on lifestyle risk factors. The fact that the maternal excess varied across categories of glucose tolerance for Europeans may make these explanations less likely. The most serious limitation of our study (in common with most other such studies) is its reliance on respondents’ reports of family histories. Uncertainty about family history is reflected in the large numbers in the missing or “don’t know” category, particularly among Europeans. Nevertheless, our findings in Europeans are consistent with previous clinic- and population-based reports. Our results in South Asians, which were derived from a population-based study, add weight to previous reports that maternal excess is not a feature of type 2 diabetes in these ethnic groups.
Any proposed explanation of the imbalances between maternal and paternal diabetes must take account of the ethnic differences we have described. Such an explanation will likely make an important contribution to understanding the high prevalence of type 2 diabetes in South Asians in the U.K. and elsewhere. We need further studies based on biochemical information about family members of people with type 2 diabetes.
Family history of maternal and paternal diabetes by ethnic group and respondent glucose tolerance status
| . | Normal . | Impaired glucose tolerance . | Diabetes . |
|---|---|---|---|
| Europeans | |||
| n (% don’t know/missing) | 649 (27) | 129 (29) | 46 (33) |
| Maternal diabetes only | 6.3 (4.3, 8.9) | 8.7 (3.8, 16.4) | 32.3 (16.7, 51.4) |
| Paternal diabetes only | 2.1 (1.0, 3.8) | 3.3 (0.7, 9.2) | 3.2 (0.1, 16.7) |
| Difference | 4.2 (1.5, 6.3) | 5.4 (−2.6, 10.5) | 29.0 (6.3, 35.3) |
| South Asians | |||
| n (% don’t know/missing) | 386 (14) | 140 (14) | 158 (18) |
| Maternal diabetes only | 12.1 (8.8, 16.1) | 14.2 (8.5, 21.7) | 10.9 (6.1, 17.5) |
| Paternal diabetes only | 8.5 (5.7, 12.0) | 15.0 (9.1, 22.7) | 7.8 (3.8, 13.8) |
| Difference | 3.6 (1.5, 8.5) | −0.8 (−10.9, 9.3) | 3.1 (−5.0, 10.4) |
| . | Normal . | Impaired glucose tolerance . | Diabetes . |
|---|---|---|---|
| Europeans | |||
| n (% don’t know/missing) | 649 (27) | 129 (29) | 46 (33) |
| Maternal diabetes only | 6.3 (4.3, 8.9) | 8.7 (3.8, 16.4) | 32.3 (16.7, 51.4) |
| Paternal diabetes only | 2.1 (1.0, 3.8) | 3.3 (0.7, 9.2) | 3.2 (0.1, 16.7) |
| Difference | 4.2 (1.5, 6.3) | 5.4 (−2.6, 10.5) | 29.0 (6.3, 35.3) |
| South Asians | |||
| n (% don’t know/missing) | 386 (14) | 140 (14) | 158 (18) |
| Maternal diabetes only | 12.1 (8.8, 16.1) | 14.2 (8.5, 21.7) | 10.9 (6.1, 17.5) |
| Paternal diabetes only | 8.5 (5.7, 12.0) | 15.0 (9.1, 22.7) | 7.8 (3.8, 13.8) |
| Difference | 3.6 (1.5, 8.5) | −0.8 (−10.9, 9.3) | 3.1 (−5.0, 10.4) |
Data are n (%) or % (95% CI).
Article Information
We acknowledge financial support from the Barclay Trust, the British Diabetic Association, the Newcastle Health Authority, the research and development directorate of the former Northern Regional Health Authority, the U.K. Department of Health, and the British Heart Foundation.
The authors thank all those mentioned in the acknowledgments of their previous study (4) and Louise Hayes for help with data management.
Material in this letter was previously presented at the Society for Social Medicine’s 44th Annual Scientific Meeting in Norwich, U.K., in September 2000.
References
Address correspondence and reprint requests to Dr. Colin M. Fischbacher, Lecturer in Public Health Medicine, Department of Epidemiology and Public Health, The Medical School, University of Newcastle, Newcastle upon Tyne, NE2 4HH, U.K. E-mail: [email protected].
