Hereditary Ataxia

The two categories of hereditary ataxia are dominant or recessive.  When a disease is expressed in the DNA of one of the non-sex chromosomes, it is called autosomal.  If the abnormal gene is in one of the sex chromosomes, it is called sex-linked.

If the gene specific for a disease is dominant, the symptoms for that disease will occur when the individual inherits one copy of the gene.  This means that the chance of inheriting the abnormal gene from one parent is 50 percent. Therefore, for dominant hereditary ataxia, one in two of the children of an affected parent will have ataxia.

In recessive ataxia, a person inherits genes from both parents to develop the disease.  While both parents must be carriers of the gene, neither parent will have symptoms of ataxia because each parent has only one copy of the gene. However, some of their children will acquire a copy of the faulty gene from each parent causing symptoms of ataxia.  Recessive ataxias occur in 25 percent--or one in four--of children who have two parents carrying the ataxia gene.

For most types of dominant ataxia, the symptoms include impaired coordination of movement that affect speech, gait, and/or movement of the arms, legs, and eyes. The term used to name most dominant ataxias is Spino-Cerebellar Ataxia (SCA) followed by a number (e.g., SCA-1 to SCA-28). In addition, there are different types (e.g., Dentatorubral Pallidoluysian atrophy [DRPLA] or Haw River Syndrome).

The following is a list of relatively common dominant ataxias. These types are caused by known abnormal genes and genetic tests are usually available for identification.

• Friedreich's ataxia
• Ataxia with oculomotor apraxia
• Autosomic recessive spastic ataxia of Chalevoix-Saguenay (ARSACS)