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Fragile X syndrome (FXS) is a genetic neurodevelopmental disorder characterized by mild-to-moderate intellectual disability. [1] The average IQ in males with FXS is under 55, while about two thirds of affected females are intellectually disabled.
While initially described as affecting male carriers, female carriers of the FMR1 gene mutation have also been found to develop FXTAS. However, due to X-inactivation, female carriers are much less likely to develop dementia or classic ataxia and tremor, instead demonstrating symptoms such as fibromyalgia, thyroid disease, hypertension, and ...
Fragile X-associated primary ovarian insufficiency (FXPOI) is the most common genetic cause of premature ovarian failure in women with a normal karyotype 46,XX. [1] The expansion of a CGG repeat in the 5' untranslated region of the FMR1 gene from the normal range of 5-45 repeats to the premutation range of 55-199 CGGs leads to risk of FXPOI for ovary-bearing individuals. [2]
Sherman theorized that the gene responsible for fragile X syndrome becomes mutated through a two-step process. The first mutation, called the 'premutation', doesn't cause any clinical symptoms. A second mutation was required to convert the 'premutation' into a 'full mutation' capable of causing the clinical symptoms associated with fragile X ...
46,XX/46,XY chimeric or mosaic is associated with a wide spectrum of different physical presentations, with cases ranging from having a completely normal male or female phenotype [7] [8] [9] to some cases having ovotesticular syndrome. Due to this variation, genetic testing is the only way to reliably make a diagnosis.
X-linked genetic disorders can arise when there is a spontaneous and permanent change in the DNA sequence of an X-linked gene, known as mutation. Traits or diseases caused by X chromosome genes follow X-linked inheritance, the difference between recessive and dominant inheritance affects the probability of an offspring acquiring it from the ...
XX gonadal dysgenesis is a type of female hypogonadism in which the ovaries do not function to induce puberty in a person assigned female at birth, whose karyotype is 46,XX. [1] Individuals with XX gonadal dysgenesis have normal-appearing external genitalia as well as Müllerian structures (e.g., cervix, vagina, uterus).
When X-inactivation occurs randomly, half of the cells in the carrier female would contain the abnormality. [9] When X-inactivation is skewed, more than 50% of one X chromosome are becoming inactive, and if that X-chromosome is passed to a male, they will have a higher percent of heterochromatin. [ 9 ]