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patient information. Founded in 1981, the center publishes a monthly newsletter. For address, see Appendix I.

forebrain The largest and most expansive part of the brain is made up of two subdivisions: the telencephalon (endbrain) and the diencephalon (inter-brain). Structures in the telencephalon account for about 75 percent of the weight of the entire central nervous system and include the cerebral hemispheres connected by a mass of crossing fibers in the corpus callosum and preoptic area. The surface of the hemispheres is a layer of tissue called the cerebral cortex, which is divided into subre-gions according to creases along the brain's surface (also known as sulci). The largest subregions are the four lobes in each hemisphere (frontal, parietal, temporal, and occipital).

The cerebral hemispheres are attached to the diencephalon by large bundles of fibers called the corona radiata. The major parts of the diencephalon include the thalamus, the subthalamus, the hypothalamus, and the epithalamus (containing the pineal body).

fornix A circular arrangement of fibers connecting the hippocampus to the hypothalamus and connecting the two hippocampi.

Fragile X Foundation A support organization concerned with fragile x syndrome and other forms of X-linked mental retardation. The group seeks to educate and provide information about diagnosis and treatment. The foundation also encourages research and publishes materials including a quarterly newsletter and a brochure. For address, see Appendix I.

See also fragile x support.

Fragile X Support A national support organization concerned with fragile x syndrome, the group helps families in enhancing the lives of children with the condition, provides information, and publishes brochures. For address, see Appendix I.

See also fragile x foundation.

fragile X syndrome An X-linked congenital condition caused by a chromosomal abnormality in which a male's x chromosome is malformed; some evidence links the syndrome with autism or learning DISABILITIES.

Many children with fragile x are mentally retarded (as often are their mothers), but others with the syndrome have normal mental capacity. In fact, fragile X is the most common cause of mental retardation in males after down syndrome. Although males are mainly affected, women are able to carry the genetic defect that is responsible for the disorder and pass it on to some of their sons, who are affected, and some of their daughters, who in turn become carriers of the defect. Approximately one in 1,500 men are affected and one in 1,000 women are carriers. About one-third of female carriers show some degree of intellectual problems.


In addition to mental retardation, the syndrome is characterized by large testicles, protruding long ears, and a pronounced nose, chin, and forehead; those affected tend to be tall and physically strong. The syndrome affects every 2,000 to 3,000 births; a child of a mother who carries the fragile X chromosome has a one chance in two of inheriting the disorder.


There is no treatment.

See also fragile x foundation; fragile x support.

free radicals A highly charged, potentially destructive molecule (most commonly, a species of oxygen) that is generated naturally by breathing and by the body's response to stress. While free radicals are destructive, they have a positive role to play in the body as well. Generated by the immune system, they fend off microbes and help the digestive system break down food. In the brain, it can interact with lipids, harming the brain.

While a certain amount of free radicals is necessary to maintain proper body function, high levels are toxic. Each day, the body generates thousands upon thousands of free radicals in response to ultraviolet (UV) light, smoke, and pollution. Once activated, they tear through the membrane that protects the body's cells, causing inflammation and cell breakdown.

Friedreich's ataxia A hereditary degenerative disease that damages the nervous system, characterized by the development of muscle weakness. The condition is named after the physician Nicholas Friedreich, who first described the disease in the 1860s. In Friedreich's ataxia, coordination problems are caused by degeneration of nerve tissue in the spinal cord and of nerves that control muscle movement in the arms and legs. The spinal cord becomes thinner and nerve cells lose some of their myelin sheath (the covering on all nerve cells that helps conduct nerve impulses), a process known as demyelination.

Friedreich's ataxia, although rare, is the most prevalent inherited ataxia, affecting about one in every 50,000 people in the United States. Men and women are affected equally.


Friedreich's ataxia is an autosomal recessive disease, which means the patient must inherit two affected genes, one from each parent, for the disease to develop. A person who has only one abnormal copy of a gene for a recessive genetic disease such as Friedreich's ataxia is called a carrier. A carrier will not develop the disease but could pass the affected gene on to his or her children. If both parents are carriers of the Friedreich's ataxia gene, their children will have a one in four chance of having the disease and a one in two chance of inheriting one abnormal gene that they, in turn, could pass on to their children. About one in 90 Americans of European ancestry carries one affected gene.


Symptoms usually begin between the ages of five and 15 but can, on rare occasions, appear as early as 18 months or as late as age 30. The first symptom to appear is usually difficulty in walking (gait ataxia). This gradually worsens and slowly spreads to the arms and then the trunk. Foot deformities such as clubfoot, involuntary bending of the toes, hammer toes, or foot inversion (turning inward) may be other early signs.

over time, muscles begin to weaken and waste away, especially in the feet, lower legs, and hands, and deformities develop. Other symptoms include loss of tendon reflexes, especially in the knees and ankles. There is often a gradual loss of sensation in the extremities, which may spread to other parts of the body. Slowness and slurring of speech develops, and the person is easily tired. Rapid, rhythmic, involuntary movements of the eyeball (nystagmus) is common. Most people with Friedreich's ataxia develop scoliosis (a curving of the spine to one side), which, if severe, may impair breathing.

other symptoms that may occur include chest pain, shortness of breath, and heart palpitations. These are caused by various forms of heart disease that often accompany Friedreich's ataxia, such as cardiomyopathy (enlargement of the heart), inflammation of the walls of the heart (myocarditis), formation of fibrous material in the muscles of the heart (myocardial fibrosis), and cardiac failure. Heart rhythm abnormalities such as fast heart rate and heart block are also common.

About 20 percent of people with Friedreich's ataxia develop carbohydrate intolerance and 10 percent develop diabetes mellitus. Some people lose hearing or eyesight.

The rate of disease progression varies from person to person, but generally within 15 to 20 years after the appearance of the first symptoms the person is confined to a wheelchair. In later stages of the disease, individuals become completely incapacitated.

Most people with Friedreich's ataxia die in early adulthood if there is significant heart disease, which is the most common cause of death. However, some people with less severe symptoms of Friedreich's ataxia live much longer.

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