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Is fragile X syndrome recessive or dominant, because some sources say it's recessive and some say it's dominant, I'm confused :!:


its X linked dominant disease


It is currently unclear whether this trait is dominant or recessive, because both types of expression have been demonstrated.


A person with fragile X syndrome has a mutation in the FMR1 (fragile X mental retardation 1) gene in the DNA that makes up the X chromosome. That mutation causes the cell to methylate a regulatory region of the FMR1 gene. The methylation turns off the FMR1 gene. Since the gene is turned off, the person doesn't make FMRP. That lack of a specific protein triggers fragile X syndrome.
Since the FMR1 gene is on the X chromosome, and since it has a tendency to mutate once it has become a premutation, the patterns of inheritance for fragile X syndrome are complex.
Once the FMR1 gene changes from stable (standard) to unstable (premutation), it has a high probability of mutating from one generation to the next. Thus, there can be a family with no history of fragile X syndrome in which it suddenly appears in a number of offspring.


Thanks to all, I understand it much better now :icon_salut:

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