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 Fragile X syndrome  

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I have become confused about mode of inheritance of fragile x syndrome .. as far i know from goljan and my knowledge its a x-linked recessive disease but in the kaplan video lecture of genetics the old guy is saying its a good example of x linked dominant disease ..which one is correct.can anybody please clear my confusion ?


i was under the impression that XLR is usually passed from mom to son, and that XLD is from father to daughter, so it makes sense that Fragile X is XLR (and a triple repeat disorder); i too have alwys heard x-linked recessive; i thought the only x-linked dominant was one form of rickett's and pseudohypoparathyroidism, no??

hope i helped and didn't confuse u more! shocked


thats a lot ..I also think its XLR . And XLD diseases are familial hypophosphatemia and alport's syndrome .


crap, haha.. i knew it was hypo- something, hahha.. alports huh?? hmm, interesting, thanx for that!! nodnodnod




hey i saw u msg, my exam rite now is scheduled for 22, but i may have to move it confused

not sure yet, havnt just sat down to focus, which i need to do, so have been doing goljan daily with sutdy partner, but not yet doing FA which i should do.. and totally stopped questions.. i am doing usmlerx which goes with FA so i had hoped i would cover it with that.. but have not been doing questions either..

we shall see.. when is u test?


I thought that fragile X syndrome follows Nonmendelian inheritance pattern, so it is not X -linked at all...


fragile X syndrome is X linked recessive disorder....
Technically, fragile X syndrome is an X-linked dominant condition with reduced penetrance.
Because males normally have only one copy of the X chromosome, those males with significant trinucleotide expansion at the FMR1 locus are symptomatic. They are intellectually disabled and may show various physical features of the fragile X syndrome.
Females have two X chromosomes and thus have double the chance of having a working FMR1 allele. Females carrying one X chromosome with an expanded FMR1 gene can have some signs and symptoms of the disorder or be normal. Although the extra X chromosome can serve as a backup, only one X chromosome is active at a time due to X-inactivation.

Males with the fragile X cannot transmit it to any of their sons (since males contribute a Y chromosome, not an X, to their male offspring), but will transmit it to all of their daughters, as males contribute their X to all of their daughters.

Females carrying one copy of the fragile X can transmit it to their sons or daughters; in this case each child has a 50% chance of inheriting the fragile X. Sons who receive the fragile X are at high risk of intellectual disability. Daughters who receive the fragile X may appear normal or they may be intellectually disabled, usually to a lesser degree than boys with the syndrome. The transmission of fragile X often increases with each passing generation..


It seems to be so easy. Thank you.

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