By contrast, relatively fewer (to date, up to four replicated: MED17, MED20, MED23, and MED25) mutations in the other 26 non-Module components of the Mediator have been described; bi-allelic mutations in MED17 or MED20 (both members of the Mediator’s Head) produce progressive cerebral and/or cerebellar atrophy, whereas bi-allelic mutations in MED23 or MED25 cause syndromic or non-syndromic ID (summarized in Table S3). The gene discussed is MED20; the disease is Cerebellar atrophy.