This occurs in one in 2,500 live female births. It is caused by either the absence of or an abnormality in one of the two X CHROMOSOMES. Classical Turner's syndrome is a complete deletion of one X so that the GENOTYPE is 45XO. Half of the people with Turner's syndrome have MOSAICISM with a mixture of Turner cells and normal cells, or other abnormalities of the X chromosome such as partial deletions or a ring X. They are females, both in appearance and sexually; clinical features are variable and include short stature, with final height between 1.295 m and 1.575 m, and ovarian failure. Other clinical features may include a short neck, webbing of the neck, increased carrying angle at the elbow (cubitus valgus), widely spaced nipples, cardiovascular abnormalities (of which the commonest is COARCTATION OF THE AORTA [about 10 per cent]), morphological abnormalities of the kidneys (including horseshoe kidney and abnormalities of the pelviureteric tracts), recurrent otitis media (see under EAR, DISEASES OF), squints, increased incidence of pigmented naevi (see NAEVUS), hypothyroidism (see under THYROID GLAND, DISEASES OF) and DIABETES MELLITUS. Intelligence is across the normal range, although there may be specific learning difficulties related to hand-eye coordination and spatial awareness.

Patients with Turner's syndrome may require therapeutic help throughout their life. In early childhood this may revolve around surgical correction of cardiovascular disease and treatment to improve growth. PUBERTY may need to be induced with oestrogen therapy (see OESTROGENS) and both growth hormone and oxandrolone have been used to increase final height. In adult life, problems of oestrogen therapy, prevention of osteoporosis (see under BONE, DISORDERS OF), assessment and treatment of HYPERTENSION and assisted fertility predominate.