Phenotypic differences and similarities of monozygotic twins with maturity‐onset diabetes of the young type 5

Here, we report phenotypic differences and similarities of monozygotic twins with maturity‐onset diabetes of the young type 5 harboring a partial deletion of chromosome 17q12. The proband and her twin sister manifested complete aplasia and marked hypoplasia, respectively, of the body and tail of the pancreas. Whereas both twins showed marked hypoplasia of the right kidney and multiple cysts in both kidneys, only the proband's sister showed hydronephrosis in the left kidney. The proband had profound defects in insulin and glucagon secretion, as well as mild renal dysfunction, whereas her sister had pronounced renal dysfunction accompanied by mild defects in insulin and glucagon secretion. Both twins manifested hypomagnesemia and hyperuricemia, but no apparent liver dysfunction or intellectual disability. The severity of renal and pancreatic defects differed between monozygotic twins with maturity‐onset diabetes of the young type 5, suggesting that the phenotypes of this condition are determined not solely by genetic factors.