There are a number of other X chromosome abnormalities.
48,XXXX and 49,XXXXX syndromes
These women with more than 3 x chromosomes do exist. However, if there are more than 3 X chromosome, the degree of mental retardation is getting very severe. Also the amount of associated congenital abnormalities in various organ systems increases markedly.
48,XXXX Syndrome (or Tetrasomy X)
48,XXXX syndrome is also known as tetrasomy X. Patients with tetrasomy X have a characteristic face with epicanthal folds, a small mouth and a cleft palate or high arched palate. Teeth can be missing or be delayed with enamel defects. There is moderate mental retardation with an IQ of 60 to 70. Developmental delays are common with walking occurring at only 1 ½ to 4 years. Puberty is normal in half the cases, the others have significant delays or fail to develop secondary sexual characteristics. Many XXXX syndrome girls have menstrual irregularities and premature menopause, often in their teens. Maldeveloped eyes (microphthalmos) and optic nerve hypoplasia can cause severe visual loss or blindness. Otherwise myopia and nystagmus are common. Severe heart and kidney abnormalities are common. Seizures without documentable brain abnormalities also are found not infrequently. Ear abnormalities affecting hearing are common as a re recurrent ear infections. The prognosis of tetrasomy girls is relatively good, if mental retardation is not too severe. Many will need estrogen therapy during puberty to help initiate breast development. Otherwise speech therapy, learning assistance and physical therapy is often required.
XXXXX syndrome (or pentasomy X)
There is another rare chromosomal abnormality where five X chromosomes are present, which is called pentasomy X. Children with this genetic abnormality have microcephaly and micrognathia (small head and small jaw). The neck is webbed much like Turner syndrome. There is scoliosis and hypotonia (weak muscles). Toes are overlapping. The mouth often shows a cleft palate, a highly arched palate and dental abnormalities. They often have severe cardiac abnormalities and kidney defects. There is retarded growth and severe mental retardation with an IQ of only 45 to 55.
2. Goldman: Cecil Medicine, 23rd ed., copyright © 2007 Saunders, An Imprint of Elsevier: CHROMOSOMAL DISORDERS