Iman M Talaat and Naglaa Mohamed Kamal
Insulin gene mutation (INS) is the second most common cause of permanent neonatal diabetes (PNDM). We present the 1st cases of Saudi monozygotic twins with permanent neonatal diabetes mellitus who had simultaneous onset of disease due to p.C109Y (p.Cys109Tyr, c.326G>A) heterozygous missense mutation in exon 3 of the insulin (INS) gene. The twin patients had the same mutation while their parents are unaffected with normal genetic testing suggesting that this mutation had raised de novo. This p.C109Y mutation affects a highly conserved cysteine residue which is crucial for protein folding. Subjects with this form of diabetes will need lifelong insulin therapy.