Tetrasomy 18p de novo: parental origin and different mechanisms of formation

Eur J Hum Genet. 1996;4(3):160-7. doi: 10.1159/000472190.


We have used eight PCR-based DNA polymorphisms to determine the parental origin and mechanisms of formation in 9 patients with de novo nonmosaic tetrasomy 18p. The 9 patients, 4 girls and 5 boys, had clinical features characteristic of i(18p) syndrome. The supernumerary marker chromosome was identified by fluorescence in situ hybridization (FISH) analysis using centromeric probes and a flow-sorted 18p-specific library. The isochromosome was of maternal origin in all 9 cases. The formation of tetrasomy 18p cannot be explained by a single model. In 6 cases, meiosis II nondisjunction, followed by subsequent postzygotic misdivsion, and in 1 case postzygotic nondisjunction and postzygotic misdivision were the most likely mechanisms of formation. Alternative mechanisms are suggested in the remaining 2 cases.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aneuploidy*
  • Child
  • Child, Preschool
  • Chromosome Mapping
  • Chromosomes, Human, Pair 18*
  • Female
  • Humans
  • In Situ Hybridization, Fluorescence
  • Infant
  • Male