Abstract
Ten patients with otosclerosis and four normal relatives of such patients were studied. Skin, fibroblast or blood short-term cultures were performed in each case and chromosomal number and morphology were analysed. In four cases trisomy and tetrasomy for chromosome number 13 were observed. The other cases showed mosaicisms with 46/47/48 chromosomes. It is suggested that trisomy and tetrasomy are due to chromosome number 13, because the extra chromosome was always the largest acrocentric of group 13–15 with big satellites.