TPMT and hyperinsulinemic hypoglycemia, familial, 4: The frequencies of TPMT genetic polymorphisms vary in different ethnic groups and TPMT deficiency cannot explain the higher incidence of adverse reactions in East Asian patients (Collie-Duguid et al., 1999; Colombel et al., 2000; Takatsu et al., 2009; Booth et al., 2011).