Pentasomy X

Pentasomy X is a sex chromosome anomaly caused by the presence of three extra X chromosomes in females (49,XXXXX instead of 46,XX).

Epidemiology

The prevalence is unknown but less than 40 cases have been described in the literature so far.

Clinical description

Pentasomy X is associated with developmental delays, short stature, craniofacial anomalies and musculoskeletal abnormalities. The craniofacial anomalies may include microcephaly, micrognathia, plagiocephaly, hypertelorism, upslanting palpebral fissures, a flat nasal bridge and ear malformations. The hands and feet are generally small and camptodactyly, clinodactyly, and radioulnar synostosis are common findings. Immunoglobulin anomalies and an increased susceptibility to infection have also been reported. Cardiovascular malformations may also be present. External genitalia are generally normal but gonadal dysfunction has been reported. Developmental profiles usually show global developmental delay and intellectual disability; however, receptive language skills are usually less severely affected than expressive language abilities.

Etiology

Pentasomy X is generally thought to arise as a result of successive maternal nondisjunction during meiosis.