Spinocerebellar Ataxia Types

“Ataxia” is the loss of control over bodily movement due to damage to the brain, for example, the presence of a tumour, or as a result of exposure to chemicals. Spinocerebellar ataxia (SCA) is caused by damage in certain chromosomes of our DNA and is genetically transmitted from a parent to child. Up to 25 spinocerebellar ataxia types have been identified, and they are named SCA Type 1, SCA Type 2, SCA Type 3 and so on, in the order in which they were discovered. The numbering does not indicate the severity of the disease.

In SCA Type 1, the cerebellum (the brain’s coordination center) degenerates when genetically impaired nerve fibres fail to transmit messages to and from the brain. Affected individuals will firstly experience poor hand coordination and difficulties with balancing while walking. They gradually find difficulty in swallowing and their speech becomes incoherent. SCA Type 1 symptoms typically show up in patients in their mid-30s. If it strikes at a later age, there is a better chance that the diseases will be less severe and the rate of deterioration slower. Patients can lead quality lives up to an average of 15 years or longer. Like the rest of the spinocerebellar ataxia types, SCA Type 1 is not sex-specific, meaning both males and females have an equal chance of inheriting it. It only takes one parent with the defective gene to pass down the disease. In North America, SCA Type 1 makes up 6% of SCA cases.

Although SCA Type 2 is more common at 15% the positive side is it usually appears later, at around the 40s-50s. Patients with SCA Type 2 also have good survival rates of up to 10-20 years. Apart from the common symptoms shared by Type 1 and Type 2, SCA Type 2 is distinguishable by slow eye movements and the loss of feelings and reflexes. It can sometimes be accompanied by dementia and Parkinson’s Disease.

SCA Type 3, also known as Machado-Joseph disease (MJD) is the most common (21%) of all SCAs and shares the same prognosis of 10-20 years. Distinguishing features of SCA Type 3 include bulging eyes, double vision, and dystonia (the sustained involuntary contraction of muscles that causes abnormal twisting or repetitive movements). Parkinsonism (the symptoms, not Parkinson’s Disease itself) may also be present. Poor sleep is also common in SCA Type 3, and patients often feel tired during the day.

Other prevalent spinocerebellar ataxia types are SCA 6, SCA 7 and SCA 8; the rest are extremely rare. Due to the overlap of symptoms, a DNA test is the only way to determine the exact SCA type. However, tests are available for only 60% of known spinocerebellar ataxia types so it is possible to get a normal result even if a patient is obviously afflicted by SCA because the test cannot identify an SCA belong to the 40%. If a family member has concerns, a supplementary neurological test may be useful.

There is no known medication to slow the progress of SCA. Instead, patients are supported to lead quality and independent lives through therapy, and with aids like canes, walkers, and motorized scooters. Modifications at home can also contribute towards enabling the affected individual to remain active. Towards the end, patients often succumb to breathing difficulties or pneumonia.