Homozygous mutation in <i>MCM7</i> causes autosomal recessive primary microcephaly and intellectual disability.

Abstract

Minichromosomal maintenance (MCM) complex components 2, 4, 5 and 6 have been linked to human disease with phenotypes including microcephaly and intellectual disability. The MCM complex has DNA helicase activity and is thereby important for the initiation and elongation of the replication fork and highly expressed in proliferating neural stem cells. Whole-exome sequencing was applied to identify the genetic cause underlying the neurodevelopmental disease of the index family. The expression pattern of <i>Mcm7</i> was characterised by performing quantitative real-time PCR, <i>in situ</i> hybridisation and immunostaining. To prove the disease-causative nature of identified <i>MCM7</i>, a proof-of-principle experiment was performed. We reported that the homozygous missense variant c.793G>A/p.A265T (g.7:99695841C>T, NM_005916.4) in <i>MCM7</i> was associated with autosomal recessive primary microcephaly (MCPH), severe intellectual disability and behavioural abnormalities in a consanguineous pedigree with three affected individuals. We found concordance between the spatiotemporal expression pattern of <i>Mcm7</i> in mice and a proliferative state: <i>Mcm7</i> expression was higher in early mouse developmental stages and in proliferative zones of the brain. Accordingly, Mcm7/MCM7 levels were detectable particularly in undifferentiated mouse embryonal stem cells and human induced pluripotent stem cells compared with differentiated neurons. We further demonstrate that the downregulation of <i>Mcm7</i> in mouse neuroblastoma cells reduces cell viability and proliferation, and, as a proof-of-concept, that this is counterbalanced by the overexpression of wild-type but not mutant <i>MCM7</i>. We report mutations of <i>MCM7</i> as a novel cause of autosomal recessive MCPH and intellectual disability and highlight the crucial function of MCM7 in nervous system development.