De novo mutations in the MiDAC HDAC complex cause a neurodevelopmental syndrome resulting from increased deacetylase activity

MIDEAS is a scaffold protein that, together with DNTTIP1, mediates assembly of the MiDAC histone deacetylase complex. Mice lacking MiDAC die before birth suggesting a key developmental function. Here, we report two unrelated individuals, with a multisystem disorder characterized by delayed speech development, joint contractures, dysmorphic features and dysmotility of the gut. Both individuals have the same de novo heterozygous mis-sense variant in MIDEAS (Tyr654Ser). A cryoEM structure of the MiDAC complex reveals that this amino acid is located in a conserved auto-inhibitory loop that covers the active site of the deacetylase enzyme. We suggest that the mutation results in loop displacement leading to elevated deacetylase activity. In support, we observe reciprocal gene expression changes in patient fibroblasts compared with a cell line following rapid MiDAC degradation. Our results establish Mideas as a novel dominant monogenic disease gene and that hyperactivity of the MiDAC complex results in a characteristic multisystem disorder.