The fact that more than half of obese insulin-resistant subjects will never develop diabetes points to susceptibility for the disease in some humans, while protective factors against the disease are present in others. Indeed, a positive family history confers a two- to threefold increased risk for the disease with a 15% to 30% risk to develop type 2 diabetes or IGT in first-degree relatives of type 2 diabetes subjects (66). The risk is even higher (around 60% by the age of 60 years) if both parents have diabetes (67). Similarly, if one twin has type 2 diabetes, the risk for type 2 diabetes mellitus in the other twin is higher in monozygotic (identical) twins (35% to 58%) as compared with dizygotic twins (around 20%) (68,69). A caveat is the presence of low birth weight in many twins, since low birth weight per se associates with increased risk of type 2 diabetes later in life (70,71).
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