rpwalavalkar
Teale Fenning Administrator
Joined: 20 Jul 2006
Posts: 973
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 Posted: Mon Apr 02, 2007 1:56 pm Post subject: Fragile X Syndrome |
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Fragile X syndrome is the most common form of familial mental retardation in males caused by triplet repeat expansion.
Certain genes have been found to be inherently unstable triplet repeat regions, with the number of triplet repeats (usually cytosine-guanine-guanine (CGG)n) varying during both meiosis and mitosis. If the number of triplet repeats reaches a critical level, the affected gene can become methylated and, thus inactivated. This can result in phenotypic abnormalities.
Affected individuals have mild to severe mental retardation, attention deficit-hyperactivity disorder, speech and language problems, narrow face with large jaw, long prominent ears, macroorchidism (in postpubertal males), and, occasionally, seizures. The incidence of the full fragile X syndrome is generally quoted as 1/1000 males and 1/2000 females.
Fragile X syndrome was originally diagnosed by culturing cells in a folate deficient medium and then assessing the cultures for X-chromosome breakage by cytogenetic analysis of the long arm of the X chromosome - Xq27-28. This technique proved unreliable for both diagnosis and carrier testing.
The fragile X abnormality is now directly determined by analysis of the number of CGG repeats and their methylation status using restriction endonuclease digestion and Southern blot analysis.
Other autosomal dominant neurologic disorders caused by triplet repeat expansion include
myotonic dystrophy,
Huntington chorea,
Friedreich ataxia,
X-linked spinal,
bulbar muscular atrophy (Kennedy's disease),
spinocerebellar ataxia.
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Dr Miss. Raj Walavalkar MBBS MRCOG
TealeFenning Administrator
SR O&G Wessex Region |
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