KMT2A gene encodes Lysine-Specific Methyltransferase 2A, a large nuclear protein belonging to the myeloid/lymphoid or mixed-lineage leukemia (MLL) family. The protein functions as an enzyme and is responsible for catalyzing the methylation of the Lysine-4 residue of histone H3, a process required for epigenetic transcriptional activation. KMT2A hence positively regulates the transcription of several target genes such as HOXA9. It is also involved in the control of circadian gene expression, PPP1R15A-induced apoptosis, cell proliferation and haematopoiesis.

MLL gene is also a frequent target for translocations. These rearrangements can lead to the fusion of the MLL gene with over 50 different partners. The resultant fusion proteins are able to transform hematopoietic cells into leukemia stem cells and hence MLL rearrangements have been implicated in Acute Myeloid Leukemia (AML), Acute Lymphoblastic Leukemia (ALL) and Mixed Lineage (biphenotypic) Leukemia (MLL).

Mutations in the gene have been associated with Wiedemann-Steiner Syndrome (WDSTS), a multi-system disorder characterized by hypertrichosis cubiti, short stature, intellectual disability and distinct facial dysmorphia. KMT2A mutations have also recently been implicated in Kabuki Syndrome 2 (KABUK2), an intellectual disability condition known for its distinct facies of long palpebral fissures and eversion of the lateral third of the lower eyelid.