What causes Fragile X Syndrome?
Fragile X syndrome is a genetic condition which is caused by a change in a gene that is inherited at the time of conception. This gene, called the Fragile X Mental Retardation 1 or FMR1 gene is found on the X chromosome. When this gene change occurs the FMR1 gene does not work properly. The FMR1 gene is responsible for making a protein that is important in brain development. Therefore when the gene is not working properly, brain function including learning, behavior and communication is affected.
A short animation from the Centers for Disease Control - National Center on Birth Defects & Developmental Disabilities
How do the changes in the FMR1 gene lead to Fragile X Syndrome?
The FMR1 gene appears in four forms that are defined by the number of repeats of a pattern of DNA called CGG repeats.
InheritanceA mother who carries Fragile X has a 50% chance of passing the mutated gene to each of her children. Her children will either be carriers or they will be have Fragile X syndrome.
Male carriers will pass the premutation to all their daughters but none of their sons. These daughters are carriers but they do not have Fragile X syndrome. The Fragile X premutation can be passed silently down through generations in a family before a child is born with the syndrome. Note: Each cell in the body contains forty-six (twenty-three pairs of) chromosomes. These chromosomes consist of genetic material (DNA) necessary for the production of proteins which lead to growth, development and physical and intellectual characteristics. The first twenty-two pairs of chromosomes are the same in males and females. The remaining two chromosomes, X and Y, determine whether a person is male or female. Males have only one X chromosome which is inherited from the mother. They receive a Y chromosome from the father. Females inherit two X chromosomes, one from each parent. |