PAX4 and maturity-onset diabetes of the young type 9: MODY9 is a rare type of MODY caused by a mutation in Paired box gene 4 (PAX4), first reported in 2007.[5] PAX4, a member of the PAX transcription factor family, plays an important role in the differentiation of pancreatic β-cells as a key regulator of early pancreatic development at the embryonic stage.[6] To the best of our acknowledge, there is no confirmed case of MODY9 in China.