What is fragile X ?

Fragile X includes a set of genetic conditions that affect individuals and families in various ways. These conditions are related in that they are all caused by changes in the same gene, called the FMR1 gene. Different changes cause different effects. Individuals with a large FMR1 gene change have fragile X syndrome.

• Fragile X Syndrome (FXS), the most common cause of inherited mental impairment, affects brain development and causes a range of disabilities from learning problems to more severe intellectual disabilities (sometimes referred to as mental retardation). FXS is the most common known cause of autism or "autistic-like" behaviors. Symptoms also can include certain physical and behavioral features and delays in speech and language development. FXS is caused by a large change in the FMR1 gene.

Carriers are individuals who have a smaller FMR1 gene change. They may be unaffected.  Some may develop problems as they get older:

• Fragile X-associated Tremor/Ataxia Syndrome (FXTAS), affects balance, tremor and memory in some older males who carry a smaller change in the FMR1 gene.
• Fragile X-associated Primary Ovarian Insufficiency (FXPOI), affects ovarian function leading to infertility and early menopause in some females who carry a smaller change in the FMR1 gene.

Since the gene change can get bigger when it is inherited by a child, the children of a carrier can have larger changes and have FXS.

Carrier mothers have a 50% chance of passing an FMR1 gene change to each of their children, both sons and daughters. Carrier fathers pass their changed FMR1 gene to all of their daughters and none of their sons. Relatives of carriers may also have changes in the FMR1 gene. In some families, many relatives are affected, whereas in other families, a newly diagnosed individual may be the first family member to show obvious symptoms.

To learn more about Fragile X, you may visit http://www.nfxf.org, the web site of the National Fragile X Foundation.