Indian Journal of Human Genetics
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ORIGINAL ARTICLE
Year : 2012  |  Volume : 18  |  Issue : 2  |  Page : 204-216

Discerning non-disjunction in down syndrome patients by means of GluK1-(AGAT) n and D21S2055-(GATA) n microsatellites on chromosome 21


1 Manovikas Biomedical Research & Diagnostic Centre; Manovikas Kendra Rehabilitation & Research Institute for the Handicapped, 482 Madudah, Plot I-24, Sector-J, Eastern Metropolitan Bypass, Kolkata, India
2 Manovikas Kendra Rehabilitation & Research Institute for the Handicapped, 482 Madudah, Plot I-24, Sector-J, Eastern Metropolitan Bypass, Kolkata, India

Correspondence Address:
Nandagopal Krishnadas
Manovikas Biomedical Research & Diagnostic Centre, Manovikas Kendra Rehabilitation & Research Institute for the Handicapped, 482 Madudah, Plot I-24, Sector-J, Eastern Metropolitan Bypass, Kolkata-700107
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0971-6866.100769

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Introduction: Down syndrome (DS), the leading genetic cause of mental retardation, stems from non-disjunction of chromosome 21. Aim: Our aim was to discern non-disjunction in DS patients by genotyping GluK1-(AGAT) n and D21S2055-(GATA) n microsatellites on chromosome 21 using a family-based study design. Materials and Methods: We have used a PCR and automated DNA sequencing followed by appropriate statistical analysis of genotype data for the present study Results and Discussion: We show that a high power of discrimination and a low probability of matching indicate that both markers may be used to distinguish between two unrelated individuals. That the D21S2055-(GATA) n allele distribution is evenly balanced, is indicated by a high power of exclusion [PE=0.280]. The estimated values of observed heterozygosity and polymorphism information content reveal that relative to GluK1-(AGAT) n [H obs =0.286], the D21S2055- (GATA) n [H obs =0.791] marker, is more informative. Though allele frequencies for both polymorphisms do not conform to Hardy-Weinberg equilibrium proportions, we were able to discern the parental origin of non-disjunction and also garnered evidence for triallelic (1:1:1) inheritance. The estimated proportion of meiosis-I to meiosis-II errors is 2:1 in maternal and 4:1 in paternal cases for GluK1-(AGAT) n , whereas for D21S2055-(GATA) n , the ratio is 2:1 in both maternal and paternal cases. Results underscore a need to systematically evaluate additional chromosome 21-specific markers in the context of non-disjunction DS.


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