PNDM caused by mutation of the pseudo‐POU domain of HNF1B due to germline mosaicism has been reported (Edghill et al., 2006; Yorifuji et al., 2004). Heterozygous HNF1B mutations have been first described in 2004 in two siblings with TNDM, and later in another patient diagnosed with PNDM, yet all presenting with variable phenotypes (pancreatic atrophy, polycystic kidney, and exocrine insufficiency (Edghill et al., 2006; Yorifuji et al., 2004). Here, HNF1B is linked to transient neonatal diabetes mellitus.