Molecular study of a consanguineous family with autosomal recessive mental retardation and speech disorder

Document Type : Original article

Authors

1 Faculty of Basic and Applied Sciences, Department of Biotechnology and Bioinformatics, Islamic International University, New Campus, Sector H-10 Islamabad, Pakistan

2 Institute of Biomedical and Genetic Engineering KRL Islamabad, Pakistan

3 Department of Bioinformatics, Shaheed Benazir Bhutto Woman University, Peshawer, Pakistan

Abstract

Mental retardation (MR) is one of the most frequently found major genetic disorders around the world, affecting 1-3% of the people in the general population. The recent advancement in molecular biology and cytogenetic study has made possible the identification of new genes for a variety of genetic disorders including autosomal recessive MR. Recessive genetic disorders are common in Pakistan due to the high rate of consanguinity. A central focus of the present study was to map and identify the disease causing gene in a mentally retarded consanguineous Pakistani family with speech disorder. The study comprises of 20 individuals including 10 patients. Genetic analysis of autosomal recessive MR and speech disorders was carried out for eight known fundamental loci sorted out on the basis of clinical features. These loci including  3p26.2, 3p21.3, 7q22, 8p22, 11p15, 14q11.2-q12, 19p13.12, and 22p13 were screened using polymorphic microsatellite markers. To identify the disease locus, genomic DNA from each individual was genotyped for homozygosity analysis. Microsatellite markers were amplified using PCR. The study provided valuable data to exclude linkage of the above mentioned loci. The absence of any linkage of the Pakistani family with autosomal recessive MR to the eight well known loci, confirms the genetic heterogeneity of MR. These results need to be verified and the candidate gene be found by a complete genome scan, which may help us in establishing the genotype-phenotype correlation of MR, improving genetic counseling, carrier screening, DNAbased prenatal diagnosis and the opportunity to develop appropriate animal models to test new forms of cell or gene therapies.

Keywords


1.  Ropers HH. X-linked mental retardation: many genes for a complex disorder, Curr Opin Genet Dev 2006;16:260-269.
2.  Al-Ansari A. Etiology of mild mental retardation among Bahraini children: a community-based case control study. Ment Retard 1993;31:140-143.
3.   Rauch A. Hoyer J, Guth S et al., Diagnostic yield of various genetic approaches in patients with unexplained developmental delay or mental retardation Am J Med Genet A 2006;140:2063-2074.
4. McLaren J, Bryson SE. Review of recent epidemiological studies of mental retardation: prevalence, associated disorders, and etiology. Am J Ment Retard 1987:92:243-254.
5.   Bennett RL, Steinhaus KA, Uhrich SB, et al, Recommendations for standardized human pedigree nomenclature. J Gene Counsel 1995:4:267-279.
6.  Sambrook J, Fritsch EF, Maniatis T. Molecular Cloning: a laboratory manual, 2nd ed. N.Y.,  Cold Spring Harbor Laboratory Press, 1995; p.1659.
7. Sayed HS, Aiysha A, Saba S, Shagufta K. Identification of LIPH gene mutation in a consanguineous family segregating the woolly hair/hypotrichosis phenotype. J Pak Med Assoc. 2011;61:1060-1064.
8.  Kryndushkin DS, Alexandrov IM, Ter-Avanesyan MD, Kushnirov VV. Yeast [PSI+] prion aggregates are formed by small Sup35 polymers fragmented. J Biol Chem 2003;278:49636-4943.
9.   http://www.ecomii.com/science/encyclopedia/human-genetics
10. http://www.ncbi.nlm.nih.gov/books/NBK21106
11. Roeleveld N, Zielhuis GA, Gabreels F. The prevalence of mental retardation: a critical review of recent literature. Dev Med Child Neurol 1997;39:125-132.
12. Leonard H, Wen X. The epidemiology of mental retardation: Challenges and opportunities in the new millennium. Ment Retard Dev Disabil Res Rev 2002;8:117-134.
13. Ropers HH, Hamel BC. X-linked mental retardation. Nat Rev Genet 2005;6:46–57.
14. Kaufman L, Ayub M, Vincent JB. The genetic basis of non-syndromic intellectual disability: A review. J Neurodev Disord 2010;2:182-209.
15. Lencz T, Lambert C, DeRosse P, et al. Runs of homozygosity reveal highly penetrant recessive loci in schizophrenia. Proc Natl Acad Sci USA 2007;104:19942-19947.
16. Najmabadi H, Motazacker MM, Garshasbi M, Kahrizi K, Tzschach A, Chen W, Behjati F, Hadavi V, Nieh SE, Abedini SS, Vazifehmand R, Firouzabadi SG, and 9 others., Homozygosity mapping in consanguineous families reveals extreme heterogeneity of non-syndromic autosomal recessive mental retardation and identifies 8 novel gene loci. Hum Genet 2007;121:43-48.
17. Rehman S, Baig SM, Eiberg H, Rehman S, Ahmad I, Malik NA, Tommerup N, Hansen L. Autozygosity mapping of a large consanguineous Pakistani family reveals a novel non-syndromic autosomal recessive mental retardation locus on 11p15-tel. Neurogenetics, 12, p. 247-251 Ropers H.H And Hamel B.C., (2005) X-linked mental retardation, Nat Rev Genet, 2011;6:46–57.
18. Jamra RA, Wohlfart S, Zweier M, Uebe S, Priebe L, Ekici A, Giesebrecht S, Abboud A, Al Khateeb MA, Fakher M, Hamdan S, Ismael A, Muhammad S, Nothen MM, Schumacher J, Reis A. Homozygosity mapping in 64 Syrian consanguineous families with non-specific intellectual disability reveals 11 novel loci and high heterogeneity. Eur J Hum Genet 2011;19:1161-1166.
19. Basel-Vanagaite L, Alkelai A, Straussberg R, Magal N, Inbar D, Mahajna M, Shohat M. Mapping of a new locus for autosomal recessive non-syndromic mental retardation in the chromosomal region 19p13.12-p13.2: further genetic heterogeneity. J Med Genet 2003;40:729-732.
20. Basel-Vanagaite L, Attia R, Yahav M, et al. The CC2D1A, a member of a new gene family with C2 domains, is involved in autosomal recessive non-syndromic mental retardation. J Med Genet 2006;43:203–210.
21. Ritvo ER, Mason-Brothers A, Menkes JH, Sparkes RS. Association of autism, retinoblastoma, and reduced esterase D activity. Arch Gen Psychiatry 1988;45:600.
22. Steele MM, Al-Adeimi M, Siu VM, Fan YS. A case of autism with interstitial deletion of chromosome 13. J Autism Dev Disord 2011;31:231-234.
23. Bradford Y, Haines J, Hutcheson H, Gardiner M, Braun T, Sheffield V, Cassavant T, Huang W, Wang K, Vieland V, Folstein S, Santangelo S, Piven J. Incorporating language phenotypes strengthens evidence of linkage to autism. Am J Med Genet 2001;105:539-547.