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Khan MA, Khan S, Windpassinger C, Badar M, Nawaz Z, Mohammad RM. The Molecular Genetics of Autosomal Recessive Nonsyndromic Intellectual Disability: a Mutational Continuum and Future Recommendations. Ann Hum Genet 2017; 80:342-368. [PMID: 27870114 DOI: 10.1111/ahg.12176] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2016] [Accepted: 10/03/2016] [Indexed: 12/19/2022]
Abstract
Intellectual disability (ID) is a clinical manifestation of the central nervous system without any major dysmorphologies of the brain. Biologically it affects learning capabilities, memory, and cognitive functioning. The basic defining features of ID are characterized by IQ<70, age of onset before 18 years, and impairment of at least two of the adaptive skills. Clinically it is classified in a syndromic (with additional abnormalities) and a nonsyndromic form (with only cognitive impairment). The study of nonsyndromic intellectual disability (NSID) can best explain the pathophysiology of cognition, intelligence and memory. Genetic analysis in autosomal recessive nonsyndrmic ID (ARNSID) has mapped 51 disease loci, 34 of which have revealed their defective genes. These genes play diverse physiological roles in various molecular processes, including methylation, proteolysis, glycosylation, signal transduction, transcription regulation, lipid metabolism, ion homeostasis, tRNA modification, ubiquitination and neuromorphogenesis. High-density SNP array and whole exome sequencing has increased the pace of gene discoveries and many new mutations are being published every month. The lack of uniform criteria has assigned multiple identifiers (or accession numbers) to the same MRT locus (e.g. MRT7 and MRT22). Here in this review we describe the molecular genetics of ARNSID, prioritize the candidate genes in uncharacterized loci, and propose a new nomenclature to reorganize the mutation data that will avoid the confusion of assigning duplicate accession numbers to the same ID locus and to make the data manageable in the future as well.
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Affiliation(s)
- Muzammil Ahmad Khan
- Genomic Core Facility, Translational Research Institute, Academic Health System, Hamad Medical Corporation, Doha, 3050, Qatar.,Gomal Centre of Biochemistry and Biotechnology, Gomal University, D.I.Khan, 29050 KPK, Pakistan
| | - Saadullah Khan
- Genomic Core Facility, Translational Research Institute, Academic Health System, Hamad Medical Corporation, Doha, 3050, Qatar.,Department of Biotechnology and Genetic Engineering, Kohat University of Science and Technology, Kohat, KPK, Pakistan
| | | | - Muhammad Badar
- Gomal Centre of Biochemistry and Biotechnology, Gomal University, D.I.Khan, 29050 KPK, Pakistan
| | - Zafar Nawaz
- Genomic Core Facility, Translational Research Institute, Academic Health System, Hamad Medical Corporation, Doha, 3050, Qatar
| | - Ramzi M Mohammad
- Genomic Core Facility, Translational Research Institute, Academic Health System, Hamad Medical Corporation, Doha, 3050, Qatar
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Shi ZY, Li YJ, Zhang KJ, Gao XC, Zheng ZJ, Han N, Zhang FC. Positive association of CC2D1A and CC2D2A gene haplotypes with mental retardation in a Han Chinese population. DNA Cell Biol 2011; 31:80-7. [PMID: 22023432 DOI: 10.1089/dna.2011.1253] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The CC2D1A and CC2D2A genes are involved in Ca(2+)-regulated signaling pathways and have recently been implicated in the etiology of mental retardation (MR). The aim of this study was to investigate whether CC2D1A and CC2D2A polymorphisms are associated with susceptibility to MR in a Han Chinese population using a family based association approach. The sample included 172 trios (parents and offspring), and all subjects were genotyped for several single-nucleotide polymorphisms covering CC2D1A and CC2D2A. Linkage disequilibrium (LD) analysis revealed that the rs6511901 and rs10410239 polymorphisms of CC2D1A were in strong LD (D'=0.865), and haplotype analysis showed evidence for over-transmission from parents to MR offspring (p=0.0009). The LD analysis also revealed that CC2D2A single-nucleotide polymorphisms rs10025837, rs13116304, and rs7661102 were in strong LD (D'=0.848), and haplotype analysis showed significant transmission disequilibrium (p=0.0004). The results suggest the involvement of CC2D1A and CC2D2A in MR in the Han Chinese population, and some specific haplotypes may be susceptible or protective.
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Affiliation(s)
- Zhang-Yan Shi
- Key Laboratory of Resource Biology and Biotechnology in Western China, Ministry of Education, Institute of Population and Health, Institute of Application Psychology, Northwest University, 229 Tai Bai Road, Xi'an, China
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Crespi B, Summers K, Dorus S. Evolutionary genomics of human intellectual disability. Evol Appl 2010; 3:52-63. [PMID: 25567903 PMCID: PMC3352458 DOI: 10.1111/j.1752-4571.2009.00098.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2009] [Accepted: 07/28/2009] [Indexed: 01/28/2023] Open
Abstract
Previous studies have postulated that X-linked and autosomal genes underlying human intellectual disability may have also mediated the evolution of human cognition. We have conducted the first comprehensive assessment of the extent and patterns of positive Darwinian selection on intellectual disability genes in humans. We report three main findings. First, as noted in some previous reports, intellectual disability genes with primary functions in the central nervous system exhibit a significant concentration to the X chromosome. Second, there was no evidence for a higher incidence of recent positive selection on X-linked than autosomal intellectual disability genes, nor was there a higher incidence of selection on such genes overall, compared to sets of control genes. However, the X-linked intellectual disability genes inferred to be subject to recent positive selection were concentrated in the Rho GTP-ase pathway, a key signaling pathway in neural development and function. Third, among all intellectual disability genes, there was evidence for a higher incidence of recent positive selection on genes involved in DNA repair, but not for genes involved in other functions. These results provide evidence that alterations to genes in the Rho GTP-ase and DNA-repair pathways may play especially-important roles in the evolution of human cognition and vulnerability to genetically-based intellectual disability.
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Affiliation(s)
- Bernard Crespi
- Department of Biosciences, Simon Fraser UniversityBurnaby, BC, Canada
| | - Kyle Summers
- Department of Biology, East Carolina UniversityGreenville, NC, USA
| | - Steve Dorus
- Department of Biology and Biochemistry, University of BathBath, UK
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