Fragile X Syndrome Research Paper

Name of Disorder
Chromosomal Location
Fragile X syndrome is the result of a mutation in the fragile X mental retardation-1 gene. This gene is located on the long arm of the X chromosome at position 27.3. This specific chromosomal site is often referred to as a fragile site (Claudia Bagni).
Type of Inheritance
Fragile X syndrome is transmitted through X-linked dominant inheritance. This syndrome exhibits incomplete penetrance, usually only penetrating approximately 80% (Peng Jin). Mothers and fathers can transmit each type of allele for the FMR1 gene onto offspring. Depending on the type of allele passed on, offspring will be affected differently. Full mutation alleles are the only alleles that will result in fragile X syndrome. However, the …show more content…
The extreme difference in frequency of occurrence between males and females is the result of random X inactivation in females. Males are hemizygous and thus must express the X chromosome they inherit, whether it be the full mutation, premutation, or normal allele (Peng Jin).
As stated above, premutation alleles can expand into full mutation alleles as they are passed from one generation to the next. Two distinct characteristics of the expanding triplet repeat sequence in premutation alleles make them more or less susceptible to expanding into full mutation alleles. The length of the CGG repeat sequence is directly related to risk of expansion. The larger the repeat sequence, the higher change of expanding into the full mutation allele. Another aspect, AGG interruptions in the CGG repeats, inversely affects the risk of expansion. Normal alleles consist of a set range of CGG repeats with several interruptions by the three base sequence AGG. These interruptions and smaller number of repeats make the normal allele very stable. However, premutation alleles with very few AGG interruptions have a much higher risk of expansion. The lack of interruptions means there is a longer sequence of perfect CGG repeats. This high frequency of uninterrupted triplet repeats increases the risk of expansion into full mutation alleles, and ultimately, in the offspring being affected by fragile …show more content…
Symptoms are usually present at a very young age and become more prominent as the affected individual ages. The most prevalent characteristic associated with fragile X syndrome is severe intellectual disability. This cognitive impairment along with several other development delays can be seen within the first couple years of life (Dana C. Crawford). Affected males generally develop different phenotypic characteristics before and after puberty. Many characteristics seem to develop at a young age, but become more prominent and profound as the affected male ages. At an early age, many children will exhibit developmental delays in being able to sit alone, walk, or speak. As the child grows older, speech development becomes even more delayed and the affected child has significant intellectual disability, usually having an IQ between 30 and 50. Children with fragile X tend to exhibit abnormal facial features, such as a large, narrow face, large ears, and a prominent jaw. After puberty, these males tend to develop abnormally large testicles and may be affected by different connective tissue disorders. People who have fragile X syndrome usually display unusual behavioral characteristics. These behaviors may include hyperactivity, anxiety, temper problems, inability to make eye contact, and behaviors similar to those seen in autistic children. Although

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