The Heritable Disorder Fragile X Syndrome,a Major Cause of Mental

Question

The heritable disorder fragile X syndrome,a major cause of mental retardation,is caused by
A) production of enzymes that break the phosphate backbone.
B) UV light.
C) X-rays.
D) presence of an extra X chromosome in the sperm or egg
E) duplication of multiple three-nucleotide repeats.

Accepted Answer

Fragile X syndrome is caused by a mutation in the FMR1 gene, which contains a repeated sequence of three nucleotides (CGG). In individuals with fragile X syndrome, the CGG sequence is repeated many more times than normal, leading to the gene being "turned off" and not producing enough of the FMRP protein. This protein is important for proper brain development and function, and its deficiency leads to the various symptoms of fragile X syndrome, including intellectual disability.