Euchromatic histone-lysine N-methyltransferase 1 (EHMT1) is a histone methyltransferase that catalyzes the methylation of lysine-9 of histone H3 (H3-K9). H3-K9 histone methylation is restricted to euchromatin and functions to epigenetically silence gene transcription. Loss of function mutations in EHMT1 cause the 9q34 subtelomeric deletion syndrome, a syndrome characterized by severe mental retardation, hypotonia, brachy(micro)cephaly, heart defects, and distinct facial anomalies. Alternate names for EHMT1 include histone H3-K9 methyltransferase 5, H3-K9-HMTase5, eu-HMTase, G9a-like protein 1, GLP1, lysine N-methyltransferase 1D, EUHMTASE1, KMT1D, and KIAA1876.