Replication error, a new hypothesis to explain the origin of a supernumerary marker chromosome in a mentally retarded boy

Hereditas. 1989;111(2):115-23. doi: 10.1111/j.1601-5223.1989.tb00385.x.


A marker chromosome present in all the lymphocytes of a mentally retarded boy (47,XY,+mar) was identified. The karyotype of all fibroblasts was normal, 46,XY. His parents had normal karyotypes. The supernumerary marker chromosome was interpreted as a dicentric palindromic chromosome iso(9) (pter----q12, q12----pter). The marker chromosome may have originated through a ligation error in a replication fork during the S-phase followed by a new replication (endoreduplication).

Publication types

  • Case Reports
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Child, Preschool
  • Chromosome Aberrations / genetics*
  • Chromosomes, Human, Pair 9* / ultrastructure
  • DNA Replication / physiology
  • Genetic Markers
  • Humans
  • Infant, Newborn
  • Intellectual Disability / genetics*
  • Karyotyping
  • Male


  • Genetic Markers