MODY5 and 17q12 Microdeletion Syndrome: Phenotype Variability, Prenatal and Postnatal Counseling

: Maturity-Onset Diabetes of the Young Type 5 (MODY5) is caused by heterozygous pathogenic variants in the HNF1B gene, encoding the transcription factor hepatocyte nuclear factor-1β. HNF1B haploinsufficiency typically leads to young-onset non-immune diabetes and highly variable renal involvement, whose more frequent features are bilateral kidney cysts and renal hypodysplasia. Kidney cysts or echogenic kidneys can be identified by ultrasonography in the prenatal period, but the renal involvement can also start in childhood or later. Notably, a recurrent microdeletion syndrome at 17q12 (deleting HNF1B plus ~15 neighboring genes) accounts for ~40-50% of cases. The 17q12 deletion is a contiguous gene syndrome and affected individuals present with a complex phenotype, including neurodevelopmental disorders, liver and pancreas abnormalities, and other congenital defects. When counseling the patient and the parents, the clinician must consider multiple factors, including the molecular defect and the age of onset of the symptoms, with particular attention to prenatal diagnosis. A multidisciplinary approach and an early diagnosis are essential for the management of these conditions.