INCIDENCE AND SIGNIFICANCE OF SUPERNUMERARY MARKER CHROMOSOMES IN PRENATAL-DIAGNOSIS

  • 1 January 1984
    • journal article
    • research article
    • Vol. 36  (5) , 1092-1102
Abstract
The finding of a supernumerary marker chromosome in amniotic fluid cells poses a considerable counseling dilemma. In 6500 cases referred to the laboratory over a 4.5-yr period, 8 such cases were identified (0.123% of all cases). In 5 of the 8 cases, a diagnosis of true mosaicism between cells with 46 and 47 chromosomes was made. In the remaining 3 cases, the marker was present in 100% of the cells. In 3 cases, the marker was determined to be familial in nature with mosaicism present in the parents of 2 of these cases. Detailed cytogenetic findings for each case are provided. In no cases were abnormalities noted in either abortuses or live borns. The high incidence of mosaicism in these cases seems to indicate a propensity for supernumerary chromosomes to be lost. Familial markers may not be passed on for many generations, and they may arise as new mutations relatively frequently. There is an urgent need for more information in the risks associated with the prenatal detection of supernumerary chromosomes. In considering the implications of the prenatal detection of marker chromosomes cases should be considered in at least 4 distinct groups: type 1, familial and nonmosaic; type 2, familial with mosaicism in either the amnioitc fluid cells, a parent, or both; type 3, de novo markers and nonmosaic: and type 4, de novo with mosaicism present in the amniotic fluid cells.