TET1 and Global developmental delay: Similarly, TET1 was shown to regulate H3K27 modification independent of its catalytic activity as a catalytic TET1 mutant expressed in embryonic stem cells or mice restored the normal pattern of H3K27me3 and normal differentiation which were deregulated in a TET-/- mutant; TET deficiency causes aberrant upregulation of (H3K4me3+; H3K27me3+) bivalent marks on developmental genes which results in developmental delays [67].