The genetic significance of accessory bisatellited marker chromosomes

• Published in: Human genetics 1983-12, Vol.65 (2), p.155-164
• Main Authors: STEINBACH, P, DJALALI, M, HANSMANN, I, KATTNER, E, MEISEL-STOSIEK, M, PROBECK, H.-D, SCHMIDT, A, WOLF, M
• Format: Article
• Language: English
• Subjects: Abortion, Spontaneous - genetics; Adult; Biological and medical sciences; Chromosome Aberrations; Congenital Abnormalities - genetics; Cytogenetics; Down Syndrome - genetics; Female; Fundamental and applied biological sciences. Psychology; Genetic Markers; Genetics of eukaryotes. Biological and molecular evolution; Human; Humans; Intellectual Disability - genetics; Male; Phenotype; Pregnancy; Prenatal Diagnosis; Risk
• ISSN: 0340-6717; 1432-1203
• DOI: 10.1007/bf00286654

Ten new cases of accessory bisatellited marker chromosomes examined in different laboratories are reported. As a basis for genetic counseling in the context of prenatal diagnosis a cytogenetic categorization of such marker chromosomes is proposed and an estimation of the genetic risk associated with each category is carried out. The results are as follows: There is no increased risk for offspring with abnormal phenotype born to a healthy carrier of an accessory bisatellited marker chromosome with either a single or two closely adjacent C-bands (Category AI or AII). The unbiased sample of cases with de novo accessory bisatellited marker chromosomes of categories AI and AII is too small to allow a satisfactory estimation of the actual risk that, in case of such a prenatal finding, the foetus may not show a normal phenotype as a consequence of the marker chromosome. There is, however, evidence that this risk may be lower than 10%. Accessory bisatellited marker chromosomes showing a discrete pattern of G- and R-bands situated between two distant C-bands (Category AIII) usually indicate a chromosomal imbalance giving rise to an abnormal phenotype. Mosaic carriers of such dicentric marker chromosomes may, however, present a normal phenotype.