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ICD-10 Q971
OMIM [2]
DiseasesDB 32625
MedlinePlus [3]
eMedicine /
MeSH {{{MeshNumber}}}

XXXXX syndrome (also called pentasomy X or 49,XXXXX) is the presence of three additional X chromosomes. Diagnosis is done by karyotyping. Approximately 25 females have been described in medical literature worldwide with this extremely rare condition. The condition was first described in 1963.


Physical traits

XXXXX syndrome is associated with microcephaly (undersized head), micrognathia (undersized jaw), and round face. The ears are generally low-set and malformed. Eyes are upslanting and show palpebral fissures, hypertelorism, and strabismus. Usually the nose is shaped with a broad and depressed nasal bridge and epicanthus, with the mouth having a cleft palate, highly arched palate, dental abnormalities, and thick, furrowed, and everted lips. The neck is webbed, much like the underarms of a woman with Turner's Syndrome. The hands and feet are small with overlapping toes, camptodactyly, clinodactyly, talipes equinovarus, and metatarsus varus. Scoliosis generally affects the spine and hypotonia affects the muscles.

Internal organs

The heart is usually affected by patent ductus arteriosus, atrial septal defect, ventricular septal defect, and aortic dextroposition. There is abnormal lobulation of the lungs and neonatal asphyxia. The ovaries are abnormally shaped with a small uterus and kidney hypoplasia.

Growth and development

XXXXX syndrome causes mental, growth, and motor retardation. There is occasional delayed puberty. Behavior and performance is affected by Opisthotonoid posture. The 'rule of thumb' states that there will be a 10 to 15 IQ point decrease for each extra X chromosome. Thus, the average IQ would be between 55 and 70.[1]



  • Linden MG, Bender BG, Robinson A (1995). Sex chromosome tetrasomy and pentasomy. Pediatrics 96 (4 Pt 1): 672–82.

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