DDHD2 and hereditary spastic paraplegia: In 2012, Schuurs-Hoeijmakers et al. reported that the complex hereditary spastic paraplegia (HSP) subtype SPG54, an autosomal recessive genetic disease, was caused by mutations in human DDHD-domain containing 2 (DDHD2) gene (10), which was subsequently confirmed by several other groups (11, 12, 13).