The pancreatic ATP-sensitive potassium (KATP) channel is a critical regulator of beta-cell insulin secretion. Heterozygous activating mutations in the KCNJ11 gene, which encodes the Kir6.2 subunit of the KATP channel, have been found to cause diabetes in the neonatal period or early infancy. This molecular study hypothesized that KCNJ11 mutations could present clinically as type 1 diabetes. So the KCNJ11 gene was screened for mutations in 29 type 1 diabetic subjects diagnosed under the age of 2 years. The study revealed one patient with the previously described R201C mutation (an arginine-to-cysteine substitution at position 201) and the patient was successfully shifted from insulin treatment to sulfonylurea.