Mutations to cyclin D2 T280 (equivalent to cyclin D1 T286) that prevent its phosphorylation by GSK3β and subsequent nuclear export leading to proteasomal degradation result in elevated cyclin D2 levels that cause megalencephaly–polymicrogyria–polydactyly–hydrocephalus syndrome (MPPH, a developmental brain disorder) [229]. This evidence concerns the gene CCND2 and Hydrolethalus.