- A series of mutations in the dihydropteridine reductase gene resulting in either abnormal RNA splicing or DHPR protein defects. Mutations in brief no. 244. Online. Smooker, P.M., Gough, T.J., Cotton, R.G., Alliaudi, C., de Sanctis, L., Dianzani, I. Hum. Mutat. (1999)