Histone demethylase required for brain development. Specifically demethylates dimethylated 'Lys-9' and 'Lys-27' (H3K9me2 and H3K27me2, respectively) of histone H3 and monomethylated histone H4 'Lys-20' residue (H4K20Me1), thereby playing a central role in histone code (By similarity). Binds 1 Fe(2+) ion per subunit. Predominantly expressed in brain. The PHD-type zinc finger mediates the binding to H3K4me3. Binding to H3K4me3 prevents its access to H3K9me2 (By similarity). Belongs to the JHDM1 histone demethylase family. JHDM1D subfamily. Contaminating sequence. Potential poly-A sequence.