Indeed, while severe inborn HNF4α deficiency is rare and leads to maturity-onset diabetes of the young 1 (MODY1)24, mild HNF4α deficiency due to HNF4A polymorphisms in either intronic or promoter regions is common and is associated with increased risk of type 2 diabetes mellitus25, 51, gestational diabetes mellitus52, metabolic syndrome, dyslipidemia53 and arterial hypertension54. Here, HNF4A is linked to type 2 diabetes mellitus.