Pathogenic variants in the cohesin loader subunit MAU2 lead to a new Cornelia de Lange Syndrome subtype.

The role of the cohesin complex depends on the cohesin loader proteins NIPBL and MAU2. While NIPBL variants are a major cause of Cornelia de Lange Syndrome (CdLS), the role of MAU2 in disease is unclear. We describe 18 individuals carrying 15 heterozygous MAU2 variants and demonstrate pathogenicity through functional analyses. MAU2 in-frame variants predominantly impair NIPBL-MAU2 interaction, whereas truncating variants cause MAU2 haploinsufficiency and lead to NIPBL reduction. Most patients exhibit a DNA methylation profile compatible with the CdLS episignature. We also identified two MAU2-specific episignatures that reflect variant-dependent molecular consequences. Affected individuals display a wide range of phenotypes, from classic CdLS to milder presentations, with short stature and microcephaly as consistent features. A heterozygous Mau2 knockout mouse model recapitulated these traits, confirming the causal role of MAU2 disruption in vivo. Our study establishes MAU2 as a new CdLS-associated gene and delineates a MAU2-related chromatinopathy with variable expressivity.