Fragile X syndrome is an inherited genetic condition associated with mental retardation. It is identified by a break, or weakness, on the long arm of the X chromosome. Since this is an abnormality of a sex chromosome which can be transmitted from parent to child, the term "sex-linked" or "X-linked" inheritance is used in the medical literature. This means that mothers are carriers and their sons are at risk of being affected, while daughters are at risk of being carriers and sometimes mildly affected. While more boys than girls are affected by fragile X, it is not transmitted from father to son.
Rett syndrome is a severe neurological disorder whose cause is presently unknown. It leads to a variety of problems, often involving mental retardation, serious motor disabilities, epileptic seizures, and difficulties with communication.
The most severe handicap in Rett syndrome is APRAXIA, which means that the will to move is present but the child is unable to carry through the movement. Most girls need assistance for all activities of daily living: feeding, dressing, toileting. Twenty five percent of girls may never walk at all, and about half of those who do walk will lose the ability at some time. Up to 50% have epileptic seizures, some of which are mild, and some of which are severe and require medication to control. One hundred percent are at risk for some degree of curvature of the spine. Surgery is usually recommended for girls with curves over 45 degrees. Many girls can be irritable, which may be related to their frustration and inability to communicate their wants and needs.