Here, it was shown that unless postprandial glucose levels were tested, 32% of TBC1D4 p.Arg684ter carriers with prediabetes (defined as fasting plasma glucose 5.6–6.9 mmol/l, 2 h 75 g OGTT plasma glucose 7.8–11.0 mmol/l and/or HbA1c 5.7–6.4% [39–46 mmol/mol]) and diabetes would remain undiagnosed [28]. This evidence concerns the gene TBC1D4 and diabetes mellitus.