Interpreting Results of Genetic Testing

Ataxias caused by repeat expansions

Normal results-Both copies of the gene have a normal number of repeats. People with normal results would not be expected to develop that type of ataxia.

Intermediate/indeterminate results-These results can be very difficult to interpret. Repeat numbers in this range may or may not cause ataxia. In some types of ataxia (SCA1 for example), additional testing may help to determine if an intermediate repeat number could cause ataxia. Some individuals with intermediate repeat numbers will not develop ataxia, but they may be at risk for passing ataxia to their children. These types of results should be very carefully interpreted by a professional who is familiar with the genetics of ataxia.

Abnormal results-One copy of the genes has an abnormal number of repeats. In these cases, there is very clear evidence that having this many repeats in one copy of the gene is enough to cause ataxia. If a person already has symptoms, then this result confirms the diagnosis. If they are asymptomatic, then they would be expected to develop this type of ataxia in the future.

Ataxias caused by sequence changes (spelling errors) in genes

Normal results-Both copies of the gene have a normal sequence. There are no changes that would cause ataxia.

Indeterminate results-A variation or variations were detected in the spelling of one copy of the genes. It is not clear if this is a normal variation, or if it is a variation that could cause ataxia. These types of changes are frequently found in ataxia testing and they can cause much confusion. It is important to note that finding these types of changes does not confirm the diagnosis of ataxia. There are some ways to help determine if one of these changes is significant-

• If there are other family members with ataxia, they can be tested to see if the genetic variation is present in everyone with ataxia.

• There may be physicians or researchers who are interested in investigating these new variants.

• With time, we will likely better understand how these genes can vary normally and what types of changes cause disease. Therefore, it is important to have your health care provider review the medical literature from time to time to see if there is additional information about your variation.

Abnormal results-a sequence change or changes were detected that are be clearly associated with ataxia. These sequence changes may have been described before in other individuals with ataxia, or they may disrupt the function of the gene in such a way that they are clearly abnormal.