PAX4 and maturity-onset diabetes of the young type 9: MODY9 was diagnosed in two unrelated patients of Russian ethnicity harboring an identical heterozygous missense mutation in exon 5 of the PAX4 gene (HG38, chr7:127615049G>A, c.191C>T, p.Thr64Ile), which has not been previously described in patients with diabetes.