Fragile X Syndrome is a dominant X- linked syndrome, meaning it affects both men and women. Since men only have one x chrolmosome, it effects them more frequently and with more severity. With inheritance, the father passes on Fragile X only to the daughters since any sons will recieve a Y chromosome from him. If the mother has Fragile X or acts as a carrier for it, there is a 50% chance her children will be affected by it.
The Fragile X mutation was discovered in 1943 by two scientists, Bell and Martin. The disease was originally named after them, but then renamed after it was found to a sex-linked condition with a "fragile" site on the X chromorosome. The mutation that causes fragile X is a CGG repeat on the X that repeats more than normal. Normally, it repeats between 6 and 55 times. Anything over 55 repeats is considered fragile x.
About 50% f women with fragile x do not show any symptoms (long face, large ears, and flat feet). Also men and women who have between 55 and 200 CGG repeats have what is called "pre-mutation" fragile x. Pre mutation is incomplete fragile x but can cause multiple issues like ovarian failure and tremor ataxia syndrome. If someone has 200 or more CGG repeats, they have complete fragile x. The greater the number of repeats, the greater the severity of the effects. Those with fragile all show a silenced FMR1 gene with no FMRP proteins.
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