Familial occurrence of isodicentric X chromosomes with different breakpoints.

We report two cases of an idic (X) chromosome found in relatives with Turner's syndrome. A 21-year-old female revealed a non-mosaic form of X isochromosome of the long arms with two C-band regions, i.e. dic(X)(qter----cen----p11::p11----cen----qter). Her 46-year-old aunt with Turner's syndrome had an X chromosome with long arm breakpoints at site q21 and chromosomal mosaicism, i.e. 45,X/46,X, dic(X)(pter----q21::q21----pter)(78/22). The relative rarity of reports about familial Turner's syndrome with structural abnormality may suggest a coincidence. However, it is difficult to exclude familial predisposition to X isochromosome formation in this family.