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Minute supernumerary marker chromosomes identified in two patients with a related, larger pseudodicentric chromosome

G Tung1, S M Covert, K L Malabed

  • 1Division of Medical Genetics, Children's Hospital Oakland, Oakland, California 94609, USA.

American Journal of Medical Genetics
|December 18, 2001
PubMed

Insights

Two cases reveal minute supernumerary marker chromosomes (SMCs) originating from larger pseudodicentric chromosomes, suggesting deletion events in centromere inactivation. These findings offer insights into SMC formation mechanisms.

Area of Science:

  • Cytogenetics
  • Molecular Genetics
  • Human Genetics

Background:

  • Pseudodicentric chromosomes (dicentric chromosomes with one inactive centromere) can arise from rearrangements.
  • Supernumerary marker chromosomes (SMCs) are small, extra chromosomes of uncertain origin.
  • Understanding the formation of these chromosomal anomalies is crucial for genetic diagnostics.

Observation:

  • Two cases presented with a minute SMC alongside a larger pseudodicentric chromosome.
  • Case 1: A phenotypically normal male with mosaicism for a psu dic(15;15) and a minute SMC of chromosome 15 origin.
  • Case 2: A fetus with mosaicism including a psu dic(22;22) associated with cat eye syndrome and a minute SMC of chromosome 14 or 22 origin.

Findings:

  • Fluorescence in situ hybridization (FISH) confirmed the origin of the minute SMCs.
  • The minute SMCs were proposed to originate from deletion of centromeric material, inactivating one centromere of a dicentric chromosome.
  • These findings suggest minute SMCs can be by-products of pseudodicentric chromosome formation.

Implications:

  • These cases provide evidence for novel mechanisms in the formation of minute SMCs.
  • The study highlights the potential for further rearrangements of larger pseudodicentric chromosomes to generate SMCs.
  • This research contributes to understanding chromosomal instability and its consequences.

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