Ataxia Health Article

Definition

Ataxia, a medical term originated from the Greek language meaning "without order," refers to disturbances in the control of body posture, motor coordination, speech control, and eye movements. Several brain areas, including the cerebellum and the spinocerebellar tracts, substantia nigra, pons, and cerebral cortex control these functions. Injuries in one or more of these areas or in the spinal cord may lead to some form of ataxia. Birth trauma, medication toxicity, drug abuse, infections, tumors, degenerative disorders, head injury, stroke, or aneurysm, as well as hereditary neurological disorders also may cause ataxia. Many different types of inherited ataxias are presently known. Examples include Machado-Joseph disease, ataxia-telangiectasia, and Friedreich ataxia.

Description

Among children without inherited neurological disorders, important causes of ataxia are medication toxicity and post-infection inflammation of the brain. The later may happen as a complication of other viral diseases, such as measles, chicken pox, or influenza. While most people recover completely, some can have permanent neurological deficits.

Accidental ingestion of some drugs may cause ataxia, seizures, sensory neuropathies, or coma and death. The chronic administration of antihistamine medication and anticonvulsive drugs may cause ataxia in children, and should not be administered without instruction of a healthcare provider. Ingestion of seafood contaminated with high levels of methyl-mercury also causes ataxia, as does accidental ingestion of solvents. Some drugs used in treating certain types of tumors, such as those in colorectal cancer, are especially neurotoxic and can induce temporary, but usually reversible ataxia. Alcoholism, metabolic disorders, and vitamin deficiencies may also lead to ataxia.

Demographics

Non-hereditary ataxia is known as sporadic or acquired ataxia. Approximately 150,000 people in the United States alone are presently affected by ataxia, either the acquired or hereditary form. Friedreich ataxia is the most common inherited ataxia, occurring in 1 out of 50,000 population.

Causes and symptoms

Ataxia may be a consequence of brain trauma, stroke, or aneurysm. Chronic and progressive ataxia is generally associated with either brain tumors or with one of the several types of inherited neurodegenerative disorders affecting one or more brain areas involved in movement and coordination control. Other neurodegenerative disorders, such as Parkinson's disease and multiple sclerosis, may present cerebellar and/or gait ataxia as one of the clinical signs. Another cause of either chronic or progressive ataxia is the congenital (present at birth) malformation of some structures of the central nervous system.

Hereditary ataxias are rare diseases, divided into two main categories according to the pattern of inheritance: autosomal dominant ataxias and autosomal recessive ataxias. Hereditary ataxias are additionally classified into types according to the affected structures and gene location of the defective chromosome. Autosomal dominant inheritance requires the presence of the mutation in only one of the two copies of a gene (maternal or paternal) to trigger the onset of the disease at some point in life, whereas autosomal recessive inheritance requires the inheritance of the mutation in both maternal and paternal genes. Other forms of hereditary ataxias are associated with metabolic disorders, such as the Maple Syrup Urine Disease, Adrenoleukodystrophy, and Refsum disease.

Autosomal Dominant Cerebellar Ataxias (ADCAs) are a group of ataxias divided into Types I, II, and III, according to the symptoms involved. Spinocerebellar ataxias (SCAs) Type 1, 2, 3, 4, 5, 6, 7, 10, and 11 belong to the ADCA group. Dominant Spinocerebellar Ataxias (SCAs) have several overlapping clinical signs, and a common feature to those belonging to the ADCA group is cerebellar ataxia, which manifests in difficulty walking and speaking. SCA1, 2, 3, and 4 may also involve partial paralysis of the eyes, slow eye movements, poor motor coordination, dementia, peripheral neuropathy (pain, numbness, or tingling sensation in the extremities of limbs and hands), optic neuropathy, and deafness. All of these symptoms are not necessarily present. SCA2 and SCA7 may also result in retinal damage, whereas those with SCA10 exhibit loss of muscle control and generalized seizures without other symptoms.