MED13L encodes a component of the Mediator complex kinase module, which functions as a transcriptional coactivator essential for RNA polymerase II-dependent gene transcription 1. As part of the CDK8-kinase module alongside MED12, CDK8, and CCNC, MED13L facilitates the transfer of genetic information from DNA-binding proteins to RNA polymerase II during transcription initiation 1. The protein plays a critical role in neurological development, as MED13L haploinsufficiency causes intellectual disability through transcriptional defects 1. De novo mutations in MED13L are associated with a neurodevelopmental syndrome characterized by intellectual disability, developmental delay, speech impairment, hypotonia, and distinctive facial features 23. Both loss-of-function mutations (deletions, duplications, nonsense, frameshift, splicing variants) and missense mutations can cause disease, with missense variants potentially associated with more severe phenotypes including epilepsy 13. Mouse models with heterozygous Med13l deletion recapitulate key syndrome features including growth delays and craniofacial anomalies 4. Additionally, MED13L appears to regulate other cellular processes, as variants at this locus associate with gut microbiota composition 5, and MED13L can induce expression of oncogenic lncRNAs in cancer contexts 6.