Genetic disorder linked to the total absence of a sexual chromosome (kariotype 45,X : 50%) or mosaicism (45,X/46,XX : 25%) or to X- chromosome anomalies (46,XX : 25%), with the following clinical manifestations: primary amenorrhea, sexual infantilism, short stature, other associated congenital anomalies (including, in many cases, a primary lymphedema of the lower limbs).