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Indian Journal of Clinical Anatomy and Physiology


Chromosomal abberrations in mental retardation: A preliminary study


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Author Details: Debasis Bandopadhyay, Sushil Kumar

Volume : 4

Issue : 2

Online ISSN : 2394-2126

Print ISSN : 2394-2118

Article First Page : 148

Article End Page : 151


Abstract

Introduction: Chromosomal anomalies that change developmental gene expression are the most common cause of mental retardation. Roughly about 10% of all mental retardation cases suffer from chromosomal abnormalities. Sub-telomeric regions of chromosomes are gene-rich regions where rearrangements and deletions can cause mental retardation which accounts for nearly 2.5% of mental retardation cases, with or without dysmorphic features. Our study focuses on mental retardation likely to be due to chromosomal aneuploidies and large structural defects. These cases were detected using conventional cytogenetic technique by peripheral blood karyotype. A total of 30 cases of mental retardation as per exclusion/inclusion criteria were referred for genetic analysis to Cytogenetic lab, Dept of Anatomy, from May 2013 to Apr 2016. A peripheral blood karyotype was carried out in all patients.
Materials and Method: 5ml of venous blood was cultured for leucocytes and subsequently karyotyped using standard protocol of Trypsin Giemsa banding. The slides were visualised for metaphase spread under oil immersion and 20 cells were captured in every case for analysis using Cytovision software.
Results: Cytogenetic analysis of peripheral blood of 30 cases of mental retardation revealed 02 Down Syndrome pure cell line, 02 Down syndrome mosaic males, 01 Down syndrome female with 14/21 translocation, 01 Fragile X Syndrome male and 24 cases with normal karyotype.
Discussion & Conclusion: In our study only 06 out of 30 cases of mental retardation showed chromosomal anomaly analysed by peripheral blood karyotype. Previous data has concluded that genetically determined mental retardation aetiology is found in less than half the number of cases. Chromosomal aberrations, single-gene disorders, and other genetic conditions account for 17 to 41% of genetic cases of MR, even with newer techniques of genetic analysis.
Karyotype is gold standard investigation for aneuploidies and large structural defects however small deletions and alterations on chromosome are often missed in conventional cytogenetic procedures. Hence it is suggested that newer molecular cytogenetic techniques like Microarray and purely molecular techniques like Polymerase Chain Reaction (PCR) be used to diagnose submicroscopic aberrations which account for majority of aetiologically undiagnosed cases of mental retardation.

Keywords
: Mental retardation, Mosaic, Karyotype, Microarray, Polymerase Chain Reaction