DNMT3B encodes a DNA methyltransferase predicted to act in de novo methylation. DNA methylation is an epigenetic modification essential to mammalian development. It is associated with several key processes such as genomic imprinting, X-chromosome inactivation, repression of repetitive elements, aging and carcinogenesis. The DNMT3B gene has also been assumed to function as a transcriptional co-repressor with CBX4 and as a gene silencer.
Given the important role DNA methylation plays in mammalian cells, defects in the gene can have severe pathological consequences. Mutations in DNMT3B have been associated with Immunodeficiency-Centromeric Instability-Facial Anomalies Syndrome 1 (ICF1).