MBD5 and neurodevelopmental disorder: Mental retardation autosomal dominant 1 (MRD1, OMIM #156200) or MBD5 haploinsufficiency is a neurodevelopmental disorder caused by heterozygous variants in MBD5 or a deletion encompassing all or part of this gene sequence on chromosome 2q23.1 (Vissers et al., 2003; Talkowski et al., 2011).