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Prenatal diagnosis of familial ring 21 chromosome

A R Melnyk1, I Ahmed, J C Taylor

  • 1Department of Pediatrics, Loyola University Medical Center, Maywood, IL, USA.

Prenatal Diagnosis
|March 1, 1995
PubMed

Insights

A rare ring chromosome 21 can be inherited from a phenotypically normal mother, posing risks for offspring. Prenatal diagnosis may show mosaicism, but infants can be born healthy with a normal karyotype.

Area of Science:

  • Genetics
  • Cytogenetics

Background:

  • Ring chromosome 21 (r(21)) is a rare chromosomal anomaly.
  • It is often linked to intellectual disability and dysmorphic features.
  • Familial r(21) can occur in phenotypically normal individuals.

Observation:

  • Phenotypically normal female carriers of familial r(21) face increased risks for offspring.
  • Risks include Down syndrome, mosaic monosomy 21, and duplications/deletions of chromosome 21.
  • Ring chromosomes exhibit mitotic and meiotic instability, complicating prenatal diagnosis.

Findings:

  • Prenatal diagnosis in a twin pregnancy revealed mosaicism (46,XX,r(21)/45,XX,-21) in one fetus and a normal male karyotype in the other.
  • Both infants were born healthy.
  • One twin exhibited a non-mosaic ring 21 karyotype in lymphocyte cultures.

Implications:

  • This case highlights diagnostic uncertainty in prenatal cytogenetics for ring chromosomes.
  • It underscores the challenges in genetic counseling when fetal abnormalities are detected.
  • Normal outcomes are possible despite initial abnormal prenatal findings in r(21) carriers.

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