Maturity-onset diabetes of the young type 3 (MODY3) is caused by hepatocyte nuclear factor 1α gene mutation and is clinically characterized by young onset and insufficient insulin secretion. We report a 19-month-old Japanese boy with a family history of young-onset diabetes who was initially diagnosed with type 1 diabetes. Mutational analysis of the hepatocyte nuclear factor 1α gene revealed a novel heterozygous frameshift mutation (c.593delA p.Lys198fs) resulting in a truncated protein in the patient and his father. The patient was diagnosed as having MODY3 and was successfully treated with insulin glargine. We could not determine the genetic or environmental factors to explain the difference in the age of disease onset within the same family. This is the youngest case of a MODY3 child presenting with overt diabetes. Our experience suggests that clinicians should always consider the possible diagnosis of MODY3 in a diabetic child with a family history of young-onset diabetes and should perform molecular investigations.
© 2013 The Authors. Pediatrics International © 2013 Japan Pediatric Society.