A 39-year-old male patient with a disharmonic intelligence profile and juvenile diabetes mellitus is described. At 14 months of age, minor facial dysmorphisms were noticed. He had delayed motor development, obesity at early age, and a diagnosis of insulin-dependent diabetes at the age of 10 years. He successfully completed secondary education and has been engaged in unskilled work activities, living independently. Upon examination, no psychiatric symptoms were present and his neuropsychological profile showed normal, although disharmonic, intellectual capacities and suboptimal social cognition. Genome wide array analysis identified an interstitial 12q24.31 deletion of 1.67Mb encompassing hepatocyte nuclear factor-1-alpha gene (HNF1A), supporting a diagnosis of maturity-onset diabetes of the young. Results are discussed in relation to the few identified or published overlapping deletions. This is the first patient with normal intelligence in whom the presence of subtle facial dysmorphisms were decisive for introducing genetic analysis that, in turn, disclosed a rare form of diabetes necessitating modifications in treatment regimen. Clinicians, including those involved in psychiatry, should be aware of the diagnostic and prognostic value of atypical physical features in patients with a long history of complicated glucose regulation. (C) 2014 Wiley Periodicals, Inc.