Heterozygous activating mutations of KCNJ11 (Kir6.2) are the most common cause 
of permanent neonatal diabetes mellitus (PNDM) and several cases have been 
successfully treated with oral sulfonylureas. We report on the attempted 
transfer of insulin therapy to glibenclamide in a 4-year old child with PNDM and 
DEND syndrome, bearing a C166Y mutation in KCNJ11. An inpatient transition from 
subcutaneous NPH insulin (0.2 units/kg/d) to oral glibenclamide (1 mg/kg/d and 
1.5 mg/kg/d) was performed. Glucose and C-peptide responses stimulated by oral 
glucose tolerance test (OGTT), hemoglobin A1c levels, the 8-point self-measured 
blood glucose (SMBG) profile and the frequency of hypoglycemia episodes were 
analyzed, before and during treatment with glibenclamide. Neither diabetes 
control nor neurological improvements were observed. We concluded that C166Y 
mutation was associated with a form of PNDM insensitive to glibenclamide.