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Cytogenetic studies in Down syndrome.

I C Verma1, S Mathew, R Elango

  • 1Department of Pediatrics, All India Institute of Medical Sciences, New Delhi.

Indian Pediatrics
|September 1, 1991
PubMed
Summary

This study analyzed 645 patients with Down syndrome, finding that 93% had free trisomy 21. Other chromosomal abnormalities like translocations and mosaicism were less common.

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Area of Science:

  • Genetics
  • Human Genetics
  • Chromosomal Abnormalities

Background:

  • Down syndrome is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21.
  • Cytogenetic analysis is crucial for diagnosing Down syndrome and identifying specific chromosomal variations.

Purpose of the Study:

  • To investigate the spectrum of cytogenetic findings in a cohort of patients diagnosed with Down syndrome.
  • To determine the prevalence of different karyotypes, including free trisomy, translocations, and mosaicism, in Down syndrome patients.

Main Methods:

  • Karyotyping was performed on peripheral blood samples from 645 patients with a clinical diagnosis of Down syndrome.
  • Standard cytogenetic techniques were employed to analyze the chromosomal makeup of each patient.

Main Results:

  • Free trisomy 21 (47,XX,+21 or 47,XY,+21) was the most frequent karyotype, observed in 600 patients (93%).
  • Translocation Down syndrome was identified in 26 cases (4%), with Robertsonian translocations being the most common type.
  • Mosaicism (e.g., 46,XX/47,XX,+21) was present in 17 patients (2.6%).
  • Two patients (0.3%) exhibited additional complex karyotypic abnormalities in conjunction with trisomy 21.

Conclusions:

  • Free trisomy 21 is the predominant cytogenetic abnormality in Down syndrome.
  • Translocation and mosaic forms of Down syndrome, while less common, represent significant variations requiring accurate diagnosis.
  • Comprehensive cytogenetic analysis is essential for characterizing the full spectrum of chromosomal abnormalities in Down syndrome.

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