Currently, there are 25 known types of SCA although there are probably others which just haven't been discovered yet. Here is a table which shows the 11 most common types (there is no ataxia #9).

Please click to zoom in:



Fig. 8 - The 11 most common types of SCA

Source: http://depts.washington.edu/neurogen/downloads/ataxia.pdf

Please be aware that numbers are not assigned to a certain type of SCA depending on the severity of the disease, but by the order in which each type was discovered.

Each type has its own characteristics such as symptoms or onset of disease. Sometimes, however, the characteristics may overlap, in which case genetic testing may be required. Currently, there is only genetic testing available for SCA types 1, 2, 3, 6, 7, 8, 10, 12, 14 and 17.

A distinct phenomenon which occurs in SCA types 1, 2, 3, and 7 is called anticipation. This means that the severity of the disease will increase with each new generation. That means the affected offspring of a person with SCA is likely to experience more severe symptoms than his/ her parent. The onset of the disease will also be earlier in the child than the parent. Later, I will show a case study which has a good example of anticipation to demonstrate how it works.