The pathophysiology of type 2 diabetes mellitus (T2DM) is closely related to that of gestational diabetes mellitus (GDM) [1]. It is well known that a family history of T2DM is an important risk factor for the development of GDM. Even after delivery, women with a history of GDM are at increased risk of developing T2DM later in life [2-4]. In a study of a Western population, familial aggregation of both T2DM and GDM was reported [5]. Family history of T2DM is an important risk factor for GDM, as has been previously reported in Koreans [6]. However, familial clustering of T2DM has not been previously reported in Korean women with GDM.

This study was conducted in Korean subjects deemed to be at high risk of developing GDM based on the incidence of T2DM in parents and siblings.

In the present study, a history of T2DM in first-degree relatives was associated with an increased risk of developing GDM. The risk of developing GDM was increased approximately two-fold in cases with a parental history of T2DM, approximately five-fold in cases with sibling history of T2DM, and approximately 6.5-fold in cases with both sibling and parental histories of T2DM. These findings indicate the familial aggregation of T2DM in Korean women with GDM, consistent with the findings of other studies performed in different ethnic groups [3,5,8].

We found no difference in the risk of developing GDM between cases with a maternal history of T2DM and those with a paternal history of T2DM. In several previous studies, maternal influence on the development GDM has been reported, as shown a high prevalence of T2DM in the mothers of women with GDM. These findings suggest that maternal genetic background and environmental factors are important in the pathophysiology of GDM [9-12]. However, other studies have not confirmed a strong influence of maternal history of T2DM [5]. Indeed, the prevalence of T2DM in a Korean population were found to be not higher in subjects whose mothers had a history of T2DM than in those whose mothers had no history of T2DM [13].

Our finding that the risk of developing GDM was not increased in cases in which both parents had a history of T2DM differed from both our own expectations and the results of a previous study [5]. Further studies using larger numbers of subjects are required to address this unexpected finding.

Our study had several limitations. First, it was conducted at a single hospital and thus does not represent the entire Korean GDM patient population. Second, our case-control study was designed such that women with GDM were definitively diagnosed, but the control group included women that had abnormal glucose tolerance in 50-g glucose tolerance test and thus did not represent normal controls. Third, analyses of disease histories were based solely on patient report and may have been affected by recall bias. Finally, the presence or absence of familial disease history was assessed purely based on the results of a questionnaire; the influence of other genetic and/or environmental influences was not evaluated. Despite these limitations, the results of our study suggest the familial aggregation of T2DM in Korean women with GDM.