47XXX

47XXX, also called triple X syndrome or Trisomy X, is a chromosomal variation in females in which an extra X chromosome is present, giving a karyotype of 47,XXX. Many individuals with this condition have normal development and are not diagnosed unless chromosomal testing is performed for another reason or during prenatal screening.

Causes and genetics: Most cases arise from nondisjunction during parental meiosis, often involving the mother, leading to an extra X chromosome in all or most cells. Some cases are mosaic, with a mixture of 46,XX and 47,XXX cells. The syndrome is usually not inherited, and recurrence risk for parents is typically low.

Clinical features: Clinical presentation varies widely. Many individuals are asymptomatic. When present, features may include taller stature, mild hypotonia in infancy, and mild delays in speech and language or early motor development. Some have learning difficulties, especially with language and reading, and subtle social or behavioral differences. Puberty and fertility are typically normal, and overall health is often good, with most individuals leading typical lives.

Diagnosis and management: Diagnosis is made by chromosomal analysis (karyotype) of blood or other tissue, and can be detected prenatally through fetal testing or after birth because of developmental concerns or other indications. Management is supportive and multidisciplinary, including educational interventions, speech and language therapy, physical therapy, and regular medical follow-up as needed.

Epidemiology: The condition is estimated to occur in about 1 in 1,000 female births, though many cases remain undiagnosed. Mosaic forms (such as 46,XX/47,XXX) occur less commonly.