Kmt2c/Mll3 Haploinsufficiency Causes Autism-like Behavioral Deficits in Mice.

KMT2C (histone lysine N-methyltransferase 2C, also known as MML3, myeloid/lymphoid or mixed-lineage leukemia 3) is a causal gene for Kleefstra syndrome 2, a rare neurodevelopmental disorder. Recent human genetic studies have identified it as a high-risk gene for autism spectrum disorder (ASD), with 79% of patients harboring KMT2C variants having ASD. However, the causal link between KMT2C haploinsufficiency and ASD remains unclear. KMT2C/MLL3 encodes a histone methyltransferase, a core protein of the KMT2C/D COMPASS (complex proteins associated with Set1) complex, which plays fundamental roles in chromatin modification, occupancy, and gene expression. The expression of KMT2C/Kmt2c peaks during the developmental period in the human/mouse brain, which indicates the critical roles of KMT2C/Kmt2c in neurodevelopment. Here, we investigated the impact of germline Kmt2c haploinsufficiency on autism-like behavioral deficits in mice, which modeled humans carrying diverse KMT2C variants. Compared with Kmt2c+/+ controls, Kmt2c haploinsufficiency mice had normal motor function without anxiety-like behaviors. Notably, Kmt2c haploinsufficiency mice exhibited autism-like social deficits and increased self-grooming in both males and females, which recapitulated the core phenotypes of ASD patients. Novel object recognition and spatial memory deficits were observed in male and female Kmt2c haploinsufficiency mice. This study reveals a causal link between Kmt2c haploinsufficiency and ASD-like behavioral deficits. These germline Kmt2c haploinsufficiency mice can be used for further studying the molecular mechanisms and developing therapeutic interventions for KMT2C haploinsufficiency-associated behavioral deficits.