A case of bisatellited-isodicentric supernumerary chromosome 15

Abstract

The frequency of extra structurally abnormal chromosomes (ESACs) is 0.2/1000 in live births and 0.6/1000 in midtrimester amniocentesis. The frequency is much higher (3.27/1000) in the mentally retarded population. Most ESACs (65%) are derived from chromosome 15. About 16% of ESAC are familial. In general, familial ESACs have no impact on the phenotype. However, the risk prediction of de novo ESACs detected prenatally is difficult. This was estimated to be ~13% by Warburton. In those cases, the exact characterisation of the ESAC is very important. The conventional cytogenetic techniques such as GTG, CBG, RFA and NOR are not always helpful in solving this problem. We report the cytogenetic findings of a case of ESAC, in which the GTG and CBG findings might lead to false diagnosis, if this chromosome were not familial (inherited).

The frequency of extra structurally abnormal chromosomes (ESACs) is 0.2/1000 in live births and 0.6/1000 in midtrimester amniocentesis. The frequency is much higher (3.27/1000) in the mentally retarded population. Most ESACs (65%) are derived from chromosome 15. About 16% of ESAC are familial. In general, familial ESACs have no impact on the phenotype. However, the risk prediction of de novo ESACs detected prenatally is difficult. This was estimated to be ~13% by Warburton. In those cases, the exact characterisation of the ESAC is very important. The conventional cytogenetic techniques such as GTG, CBG, RFA and NOR are not always helpful in solving this problem. We report the cytogenetic findings of a case of ESAC, in which the GTG and CBG findings might lead to false diagnosis, if this chromosome were not familial (inherited).