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Its prevalence has been estimated at 1 in 5,000 live births (1 in 2,500 female births).

Clinical features are heterogeneous and typical physical anomalies are often mild or absent. Short stature is present in all cases. Ovarian failure, with variable onset depending on the chromosomal anomalies, is frequent. Other visceral manifestations (bone anomalies, lymphoedema, deafness, and cardiovascular, thyroid and gastrointestinal involvement) are less common but should be screened for at diagnosis, then monitored during adolescence and adulthood.

X-chromosome monosomy is responsible for less than half of the cases of Turner syndrome and a large majority of cases are caused by the presence of a mosaicism (45,X) and/or an abnormal X or Y chromosome (deletion, isochromosome X, dicentric chromosome).

During gestation, typical forms with associated malformations can be diagnosed by ultrasound examination, but mild forms are discovered incidentally following amniocentesis performed for another indication (for example, advanced maternal age). Prenatal counseling after diagnosis of the mild forms is particularly problematic.

Management should include growth hormone therapy, which leads to a significant increase in final height.

Quality of life and social integration are better when puberty is not induced too late, and in the absence of cardiac disease or deafness. Deafness can lead to learning difficulties and, during adulthood, sterility can have a negative effect on quality of life. The prognosis depends on the presence of heart disease, obesity, arterial hypertension and osteoporosis. Therefore, long-term follow-up is necessary.