Fragile X Chromosome

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Nicole Hollenbach

November 23, 2010

Human Genetics Fall 2010

Name of Disorder:

The disease I chose to do research on is called Fragile X Syndrome (FXS).  There are a few other names this disease is also known by, such as:  Mental retardation, X-linked, associated with marXq28, X-linked mental retardation, macroorchidism, Marker X syndrome, and Martin-Bell syndrome.

Chromosomal Location:

The disease is located on the X chromosome located about 27.3 centimorgans.  This is expressed as Xq27.3.

Type of Inheritance:

The mode of inheritance of Fragile X Syndrome is X-linked.  Women have a fifty percent chance of giving Fragile X Syndrome to their offspring whether it is the pre mutation or full mutation.  If the pre mutation is given to offspring, male or female, it can expand to full mutation.  Full mutation, however, stays full.  Not all males may be afflicted with Fragile X Syndrome due to the pre mutation form of the gene, which shows no symptoms.  Males with the pre mutation will pass it on to all daughters and no sons since the daughter gets one of her Xs from the father.

Frequency of Occurrence:

The likelihood of inheriting Fragile X Syndrome is among the most common of mental retardation diseases.  One in 4,000 males are afflicted, while one in 8,000 females are afflicted.


Symptoms of Fragile X Syndrome are physical, mental, and behavioral.  However, male and female characteristics may differ.  Males typically see more affects to FXS due to females having a normal X chromosome that has normal FMRP production.  In males  with Fragile X Syndrome there are significant intellectual disabilities that can range from learning disabilities to severe mental retardation.  An average IQ for individuals affected with Fragile X Syndrome is about 50.  Physical characteristics of Fragile X Syndrome include: enlarged ears, long face with prominent chin, large testicles (males), connective tissue problems such as ear infections, mitral valve prolapse,...