This essay has been submitted by a student. This is not an example of the work written by professional essay writers.

Fragile X Syndrome as a Form of Mental Retardation

downloadDownload printPrint

Remember! This is just a sample.

You can get your custom paper by one of our expert writers.

Get custom essay

121 writers online

Download PDF

Fragile X syndrome is the most common genetically-inherited form of mental retardation currently known. In addition to intellectual disability, some individuals with Fragile X display common physical traits and characteristic facial features, such as prominent ears.

Children with Fragile X often appear normal in infancy but develop typical physical characteristics during their lifetime. Mental impairment may range from mild learning disability and hyperactivity to severe mental retardation and autism. This genetic syndrome is caused by a defect on the X chromosome. Because of scientific advances, improvements in genetic testing, and increased awareness, the number of children diagnosed with Fragile X has increased significantly over the last decade.

A substantial research effort led to the 1991 discovery of FMR-1 (Fragile X mental retardation), the gene that when damaged causes Fragile X. Although the normal function of the FMR-1 gene is not fully understood, it appears to be important early in development. The mechanism by which the normal FMR-1 gene is converted into an altered, or mutant, gene capable of causing disease symptoms involves an increase in the length of the gene. A small region of the gene, CGG, undergoes repeated duplications, forming deoxyribonucleic acid (DNA) repeats that result in a longer gene. The lengthened DNA region is susceptible to a chemical modification process called DNA methylation. When the number of repeats is small (less than 200) the individual often has no signs of the disorder.

However, in individuals with a larger number of repeats, the characteristics that are typical of Fragile X are observed. In families that exhibit Fragile X, both the number of repeats and the length of the chromosome increase with succeeding generations. The severity of the symptoms increases with the increasing length of the repeated region.Fragile X exhibits X-linkage. The effect of X-linkage is that the frequency of the syndrome is greater in males than in females. To understand the mechanism of X-linkage some background information on the organization of human chromosomes is needed.

Human females typically have two X chromosomes, and human males have one X and one Y chromosome. A female who inherits a chromosome carrying the Fragile X gene from either parent is likely to inherit a normal X chromosome from the other parent. The normal X chromosome could provide the normal gene function and mask the presence of the Fragile X gene in a female. In that case, the female would still possess the Fragile X gene and be capable of passing it on to her offspring, but she would not exhibit symptoms. She would be a “carrier.” On the other hand, a male who inherits the Fragile X gene from his mother would inherit a Y chromosome and not a normal X chromosome from his father, and therefore a male with one copy of the gene is likely to show symptoms.

We do not yet have a complete understanding of the mechanism of genetic transmission of Fragile X. For example, it is not known why approximately one-fifth of males who carry mutated forms of FMR-1 are either unaffected or only mildly affected. In some cases, a single copy of the Fragile X gene is sufficient to cause the syndrome in females. The situation is made more complex by the fact that the intensity of the symptoms increases with succeeding generations. The observable characteristics of Fragile X occur in approximately 1 in 1,000 male births and 1 in 2,500 female births.

Remember: This is just a sample from a fellow student.

Your time is important. Let us write you an essay from scratch

experts 450+ experts on 30 subjects ready to help you just now

delivery Starting from 3 hours delivery

Find Free Essays

We provide you with original essay samples, perfect formatting and styling

Cite this Essay

To export a reference to this article please select a referencing style below:

Fragile X Syndrome as a Form of Mental Retardation. (2019, January 28). GradesFixer. Retrieved August 15, 2022, from
“Fragile X Syndrome as a Form of Mental Retardation.” GradesFixer, 28 Jan. 2019,
Fragile X Syndrome as a Form of Mental Retardation. [online]. Available at: <> [Accessed 15 Aug. 2022].
Fragile X Syndrome as a Form of Mental Retardation [Internet]. GradesFixer. 2019 Jan 28 [cited 2022 Aug 15]. Available from:
copy to clipboard

Where do you want us to send this sample?

    By clicking “Continue”, you agree to our terms of service and privacy policy.


    Be careful. This essay is not unique

    This essay was donated by a student and is likely to have been used and submitted before

    Download this Sample

    Free samples may contain mistakes and not unique parts


    Sorry, we could not paraphrase this essay. Our professional writers can rewrite it and get you a unique paper.



    Please check your inbox.

    We can write you a custom essay that will follow your exact instructions and meet the deadlines. Let's fix your grades together!


    Hi there!

    Are you interested in getting a customized paper?

    Check it out!
    Don't use plagiarized sources. Get your custom essay. Get custom paper

    Haven't found the right essay?

    Get an expert to write you the one you need!


    Professional writers and researchers


    Sources and citation are provided


    3 hour delivery