In cases of patients with CAH due to homozygous <i>CYP21A2</i> variants, suspicion for UPD may be increased if the child also presents with intrauterine growth restriction (IUGR), or transient neonatal diabetes (TNDM) mellitus, associated with maternal and paternal UPD of chromosome 6, respectively. The gene discussed is CYP21A2; the disease is transient neonatal diabetes mellitus.