Fragile X syndrome is one of the most common causes of hereditary intellectual disability.
The gene responsible for the disease is known as FMR1 and it is found in the X sex chromosome. As a result, both the transmission and the severity of the disorder varies in each sex. As a general rule, men are said to suffer from it whilst women are said to transmit it.
There is a repeat region in the FMR1 gene (expansion) and its size determines whether or not the individual has the disorder or not, as indicated below. […]