TPMT and hyperinsulinemic hypoglycemia, familial, 4: Alleles *3B and *41 were not detected in the cohort, which is expected as TPMT deficiency has been predominately attributed to alleles *2, *3A, and *3C.19 Participants determined to be IMs of thiopurines thus had 1 of 3 possible TPMT diplotypes (TPMT*1/*2, *1/*3A, or TPMT*1/*3C).