Spinocerebellar ataxias (SCA) are genetic neurological diseases that cause imbalance, poor coordination, and speech difficulties. There are different kinds of SCA and this study will focus on types 1, 2,3, and 6 (SCA 1, SCA 2, SCA 3 , also known as Machado-Joseph disease and SCA 6). The diseases are rare, slowly progressive, cause increasingly severe neurological difficulties and are variable across and within genotypes. The purpose of this research study is to bring together a group of experts in the field of SCA for the purpose of learning more about the disease. The research questions are: How does your disease progress over time? What are the best ways to measure the progression? Do some genes, other than the gene that is abnormal in your disease, have any effect on the way the disease behaves? This is a nationwide study and we expect that 800 patients will participate all over the USA. The participants will be in the study for an indeterminate period of time. Study visits will be done every 6 or 12 months depending on the participating site.