Background: Parental diabetes history is a well-known risk factor for type 2 diabetes and considered strong evidence for a genetic basis of type 2 diabetes. Whether this relationship is affected by other known risk factors, specifically obesity, remains unclear, possibly due to a relative paucity of lean diabetes patients.

Methods: This issue was investigated using data from a high-risk population from Mexico (National Health Survey 2000, n = 27,349), with observations replicated using United States citizens of Mexican descent from the NHANES 2001-2002, 2003-2004 (n = 1,568).

Results: As expected, positive parental diabetes was a significant risk factor for type 2 diabetes, regardless of age, gender, or adiposity level. However, positive parental diabetes conferred greater risk in leaner individuals than in their overweight peers (P = 0.001). In other words, the effect of BMI on type 2 diabetes risk was smaller in the presence of parental diabetes history.

Conclusions: These findings suggest that parental diabetes is a stronger risk factor for type 2 diabetes in the absence of obesity. Thus lean diabetes patients could help identify type 2 diabetes susceptibility genes. This study reinforces the concept that parental diabetes and body mass index are independent type 2 diabetes risk factors, and suggests that glycemic screening may be helpful in assessing type 2 diabetes risk in individuals with parental diabetes history, regardless of their overweight status.