Abstract
Translocations are the most common type of structural chromosomal abnormalities. Unbalanced translocations are usually found in children who present with congenital abnormalities, developmental delay, or intellectual disability. Balanced translocations are usually found in adults who frequently present with reproductive failure; either subfertility, or recurrent pregnancy loss. Herein, we report the spectrum and frequency of translocations in a Sri Lankan cohort. A database of patients undergoing cytogenetic testing was maintained prospectively from January 2007 to December 2016 and analyzed, retrospectively. A total of 15,864 individuals were tested. Among them, 277 (1.7%) had translocations. There were 142 (51.3%) unbalanced translocations and 135 (48.7%) balanced translocations. Majority (160; 57.8%) were Robertsonian translocations. There were 145 (52.3%) children and adolescents aged less than 18 years with translocations, and 142 (97.9%) were unbalanced translocations. Majority [138 (95.2%)] were referred due to congenital abnormalities, developmental delay, or intellectual disability, and 91 were children with translocation Down syndrome. All adults aged 18 years or above (132) had balanced translocations. Subfertility and recurrent pregnancy loss [84 (63.6%)] and offspring(s) with congenital abnormalities [48 (36.4%)] were the most common indications in this group. Majority (68.2%) in this group were females with reciprocal translocations (55.3%). Chromosomes 21, 14, and 13 were the most commonly involved with rob(14q21q) [72 (26%)], rob(21q21q) [30 (13.7%)], and rob(13q14q) [34 (12.3%)] accounting for 52% of the translocations. Chromosomes 1, 8, 11, and 18 were most commonly involved in reciprocal translocations. The observed high frequency of chromosomal translocations in our cohort highlights the importance of undertaking cytogenetic evaluation and providing appropriate genetic counseling for individuals with the phenotypes associated with these translocations.
Highlights
Chromosomal translocations refer to exchange of chromosomal segments between chromosomes
This study aims to describe the frequency and pattern of Robertsonian and reciprocal translocations in a cohort of Sri Lankan patients referred for cytogenetic testing during a 10-year period
The sex, age, indication for referral, and the types of chromosomal translocations in patients referred for cytogenetic analysis to the Human Genetics Unit, Faculty of Medicine, University of Colombo and Asiri Centre for Genomic and Regenerative Medicine, Colombo, are maintained in anonymized databases completely delinked from the original patients
Summary
Chromosomal translocations refer to exchange of chromosomal segments between chromosomes. Two types of chromosomal translocations are described: Robertsonian translocations and reciprocal translocations [1]. In Robertsonian translocations, the breakpoints commonly occur in the short arms of two acrocentric chromosomes (homologous or nonhomologous) with subsequent fusion and formation of dicentric chromosomes. Less frequent forms of Robertsonian translocations may be caused by breakage and fusion of centromeres (centric fusion) or from breakage and fusion of one short arm and one long arm of acrocentric chromosomes, resulting in monocentric rearrangements [3, 4]. In Robertsonian translocations, the loss of gene-poor short arms of the two acrocentric chromosomes usually does not produce any phenotypic effects. Most of these individuals remain undetected until they attempt to reproduce.
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