Introduction Epigenetic regulation is one of the most fundamental mechanisms controlling gene expression in human cells. Although every somatic cell contains nearly identical DNA sequences, different cell types exhibit highly specialized functions because distinct transcriptional programs are activated or suppressed through chromatin remodeling. Histone modifications represent a major component of this epigenetic control system, regulating chromatin accessibility and transcription factor recruitment. Among the most important histone-modifying enzymes involved in enhancer activation is KMT2D, also known as Lysine Methyltransferase 2D or MLL2. KMT2D encodes a large nuclear histone methyltransferase located on chromosome 12q13.12. The protein belongs to the COMPASS-like family of chromatin regulators and primarily catalyzes mono- and di-methylation of histone H3 lysine 4 (H3K4me1 and H3K4me2). These histone modifications are characteristic epigenetic signatures of active enhancers, which ...