<i>MED12</i> Loss‐of‐Function Variants as a Cause of Congenital Diaphragmatic Hernia in Females With Hardikar Syndrome and Nonspecific Intellectual Disability

Mediator complex subunit 12 (MED12) is required for the assembly of the kinase module of Mediator, a regulatory complex that controls the formation of the RNA polymerase II-mediated preinitiation complex. MED12-related disorders display unique gender-specific genotype-phenotype associations and include X-linked recessive Opitz-Kaveggia syndrome, Lujan-Fryns syndrome, Ohdo syndrome, and nonspecific intellectual disability in males predominantly carrying missense variants, and X-linked dominant Hardikar syndrome and nonspecific intellectual disability in females known to predominantly carry de novo nonsense/frameshift and nonsense/missense variants, respectively. MED12 was previously identified as a low-penetrance candidate gene for non-isolated congenital diaphragmatic hernia (CDH+). At the time, however, there was insufficient evidence to confirm this association. In a clinical database search, we identified 18 individuals who were molecularly diagnosed with MED12-related disorders by exome or genome sequencing, including eight missense, four frameshift, two nonsense, and one splice variant. Nine of these variants have not been previously reported. Two females with nonspecific intellectual disability were found to carry a de novo frameshift variant, indicating that potentially truncating variants causing nonspecific intellectual disability are not limited to nonsense variants. Notably, CDH was reported in three out of seven females with Hardikar syndrome or nonspecific intellectual disability but was not reported in males with MED12-related disorders. These results suggest that pathogenic MED12 variants are a cause of CDH+ in females with Hardikar syndrome and nonspecific intellectual disability.