Likewise, the data from the functional analyses point to molecular mechanisms that may underlie the proposed MCPH1 mediated risk of psychosis and pathogenesis in autosomal recessive microcephaly require additional experimental validation.
Genetic and cellular studies show that MCPH1 controls neurogenesis by coordinating the cell cycle and the centrosome cycle and thereby regulating the division mode of neuroprogenitors to prevent the exhaustion of the progenitor pool and thereby microcephaly.
MCPH1 and NCAPG2 proteins interaction is known to control chromosome structure and we thus propose that double heterozygosity for null mutations of those two genes of the Condensin II system contribute to mental deficiency with severe microcephaly phenotype.
Two microcephaly-associated proteins, abnormal spindle-like microcephaly-associated protein (ASPM) and microcephalin, are involved in mitosis and DNA damage repair.
MCPH1 and abnormal spindle-like MCPH associated (ASPM) are the two known MCPH causing genes that were suggested undergone recent positive selection in human populations.
Array-based homozygosity mapping and high-resolution microarray-based comparative genomic hybridization (array CGH) revealed a deletion of approximately 150-200 kb, encompassing the promoter and the first six exons of the MCPH1 gene, one out of four genes that have been previously implicated in ARMR with microcephaly.
Microcephalin (MCPH1) and ASPM (abnormal spindle-like microcephaly associated) have been proposed as candidate genes as mutations in both genes are associated with microcephaly, and common variants of each gene are apparently under strong positive selective pressure.
At least six genes can cause this disorder and four of these have recently been identified: autosomal recessive primary microcephaly 1 (MCPH1), abnormal spindle-like, microcephaly associated (ASPM), cyclin-dependent kinase 5 regulatory subunit-associated protein 2 (CDK5RAP2) and centromere protein J (CENPJ).
We propose that the microcephaly observed in patients with MCPH1 deficiencies is due to disruption of the ATR-BRCA1-Chk1 signaling pathway that is also disrupted in Seckel syndrome patients.
Important insights into human neurogenesis are being revealed by the study of rare genetic diseases that involve primary microcephaly, illustrated by the identification of the Microcephalin, abnormal spindle in microcephaly and ataxia-telangiectasia and Rad3-related genes.