Jarid1c is a histone demethylase which specifically demethylates lysine 4 of histone H3, thereby playing a central role in the regulation of transcription and chromatin remodelling. Jarid1c demethylates the trimethylated and dimethylated lysine 4, but not the monomethylated form. Further, Jarid1c participates in transcriptional repression of neuronal genes by recruiting histone deacetylases and REST at neuron-restrictive silencer elements. Mutations in the Jarid1c gene have been associated with X-linked mental retardation.