[Y chromosome structural abnormalities and Turner's syndrome].

Although specifically male, the human Y chromosome may be observed in female karyotypes, mostly in women with Turner syndrome stigmata. In women with isolated gonadal dysgenesis but otherwise normal stature, the testis determining factor or SRY gene may have been removed from the Y chromosome or may be mutated. In other women with Turner syndrome, the karyotype is usually abnormal and shows a frequent 45,X/46,XY mosaicism. In these cases, the phenotype depends on the ratio between Y positive and 45,X cell lines in the body. When in mosaicism, Y chromosomes are likely to carry structural abnormalities which explain mitotic instability, such as the existence of two centromeres. Dicentric Y isochromosomes for the short arm (idic[Yp]) or ring Y chromosomes (r[Y]) are the most frequent abnormal Y chromosomes found in infertile patients and in Turner syndrome in mosaic with 45,X cells. Although monocentric, deleted Y chromosomes for the long arm and those carrying microdeletions in the AZF region are also instable and are frequently associated with a 45,X cell line. Management of infertile patients carrying such abnormal Y chromosomes must take into account the risk and the consequences of a mosaicism in the offspring.