Ataxia is a symptom and not a specific disease. The term “ataxia” designates troubles in the coordination of the voluntary movements. Hereditary ataxias are neurological diseases, genetic and degenerative, of the central nervous system (CNS) characterized by the degeneration of the cerebellum or the anatomical zones, including the different nerves which are attached to it.
(The central nervous system is composed of one principal element, the encephalon, which groups together: the brain, the cerebellum, the cerebellar trunk formed by the rachidian bulb and the spinal chord.)
The encephalon is responsible for the emission of nervous impulsions toward the rest of the body, the processing of information coming from the sensorial nerves, and the operations of thinking. The organs forming the CNS have their own role to play, but the brain remains the big boss. It elaborated the orders which are conducted toward the muscles. The spinal chord, protected by the spinal column, is in fact an extension of the brain. All the information which circulates from the brain to the limbs, and vice versa, passes through the spinal chord. It can act as a command centre and triggers stimulation from its own boss.
Each region of the central nervous system receives and conveys by a way of connection (the rachidian bulb constitutes a way of connection between the brain and the spinal chord), the information which should, if everything goes well, be directed toward the brain to be processed. But with ataxia, everything does not go well.
The regions of the CNS are defective as well as the ways of connection. This results in a difficulty of reception, transmission and processing of the data for the regions themselves and between them. One can observe in several cases lesions on the level of the spinal chord causing an interruption of its functions (on the level of the lesions). There can also be a poor functioning of the cerebellum (caused by the lesions) which is manifested by the inability to maintain a precise coordination of the muscles and a harmonious voluntary motor activity. All lesions susceptible to destroy or to diminish the activity of one of these regions of the nervous system bring about ataxia.
Consequently to these lesions, one observes a degeneration of the nervous cells. The mechanism of the death of neurons is very important and complex in ataxia. It is the subject of much research..
The incoordination which ensues touches on the lower and the upper limbs, the trunk, the neck, and it has repercussions on the level of walking, standing still, sitting, crawling, kneeling, crouched, etc. It also affects the fingers, the hands, speech, the larynx, ocular movements and many others.
The numerous varieties (forms) of ataxia are distinguished according to the region afflicted in the CNS.
Ataxias are classified according to:
- the mode of transmission
- the symptoms
- the age of appearance
Ataxia is caused by a gene coming from either the 2 parents or one single parent, depending on the type of ataxia.
The ataxia gene can skip generations and reappear later, which explains the effect of surprise in learning that we have transmitted the disease to our children.
For the moment, no cure is known but it is possible to treat the symptoms. Research is being carried on and it is very promising. Researchers have identified new ataxias which are presently being studied.