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Different types of mental retardation syndromes include Down syndrome, autism, microcephaly, and cretinism. Down syndrome is the most common genetic condition in the US, while autism affects people in various ways. Microcephaly is caused by underdeveloped brain growth during pregnancy, while cretinism is caused by a deficiency of the thyroid gland. Early treatment for cretinism can aid mental development, but if left untreated, the effects can be permanent.
There are different types of mental retardation syndromes that can affect people, of which Down syndrome and autism are among the best known. Microcephaly and cretinism are some forms of mental retardation caused by the underdevelopment of the brain.
Down syndrome is the most common genetic condition in the U.S. Approximately one in 691 children in the United States is born with the syndrome. The syndrome is genetic and occurs when the individual has an extra copy of chromosome 21. This genetic condition causes developmental problems in the brain. Down syndrome is easily identified by abnormal facial features such as a flat nose, thick eyelids, and large ears, among others.
Autism is among the most enigmatic of the different types of mental retardation syndromes. Autism seems to affect people in very different ways. Research has brought some understanding of this disorder, but there is still much to learn about the brain function of people with autism. It is understood that people with autism think differently from those with normal brains, which decreases social interaction skills, but sometimes also increases skills in areas such as mathematics. Verbal skills are typically underdeveloped, and eye contact is rare in people with this disorder.
One of the mental retardation syndromes caused by impaired brain development is called microcephaly. The name literally means little dizziness, because the brain, and consequently the head, is underdeveloped during pregnancy. The appearance of each child with mecrocephaly will vary somewhat, but affected individuals tend to have a head about 17 inches (43.18 cm), compared to a normal head size of about 22 inches (55.88 cm), and often they have a cone also in the shape of a skull. These children have very limited mental capacity and tend to develop very few language skills.
Cretinism is a type of mental retardation syndrome caused by a deficiency of the thyroid gland. This disorder is sometimes caused during fetal development when the thyroid gland is underdeveloped, but it can also be caused in adulthood by injury to the thyroid gland. Some diseases, such as measles, diphtheria and whooping cough, can cause this ailment when bleeding enters the thyroid gland. Early treatment has shown some success in aiding mental development, but if no treatment is received within the first year of life, the effects are often permanent.
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