The function of ENSG00000127663 (KDM4B, lysine demethylase 4B) is as follows. Histone demethylase that specifically demethylates 'Lys-9' of histone H3, thereby playing a role in histone code. Does not demethylate histone H3 'Lys-4', H3 'Lys-27', H3 'Lys-36' nor H4 'Lys- 20'. Only able to demethylate trimethylated H3 'Lys-9', with a weaker activity than KDM4A, KDM4C and KDM4D. Demethylation of Lys residue generates formaldehyde and succinate (PubMed:16603238, PubMed:28262558). Plays a critical role in the development of the central nervous system (CNS). {ECO:0000250|UniProtKB:Q91VY5, ECO:0000269|PubMed:16603238, ECO:0000269|PubMed:28262558}.