Written by Anirudh Koneru
Published on 8/9/2020
SCA2, or spinocerebellar ataxia type 2, is a rare progressive neuromuscular disorder. It leads to a host of neurological symptoms, the primary one being ataxia (i.e. difficulty moving, hence the name: a-, a prefix that means without, and taxia, which comes from “taxis” the Greek word for movement ) that can interfere with a person’s ability to function in daily life. The symptoms and progression of the disease vary for each patient, and while symptoms usually appear in middle adulthood they may begin as early as childhood or as late as late adulthood.
Symptoms
As a neuromuscular disease, SCA2 affects both the nervous and muscular systems in a variety of ways. The initial symptom in most patients with SCA2 is ataxia: this is a difficulty moving that steadily gets worse as the disease progresses. Another common symptom that starts relatively early with the onset of the disease is leg and muscle cramps.
As the condition increases in severity, more neuromuscular symptoms become apparent. Muscle tremors and decrease in muscle tone often occur, accompanied by poor tendon reflex and abnormal eye movements. Polyneuropathy, or nerve swelling and irritation, can also occur. A range of symptoms commonly referred to as Parkinsonism (involving tremors, slow/impaired movement, speech difficulties/muscle stiffness) may also be typical of patients with SCA2.
Usually, patients who have lived with the disease for longer will also begin to develop difficulties in speech and swallowing, and there is a potential for the development of dementia.
Etiology (The Cause of the Disease)
SCA2 is a genetic condition that is inherited in an autosomal dominant pattern linked to the 12th chromosome. This means that if an individual does not have the disease, they cannot pass it on to their children; essentially, this disease cannot be secretly “carried.” However, if an individual does have the disease, they have a good chance of passing the disease on to their children. Usually this chance is 50%, but it can be more if both parents have the disease or if the parent with the disease has two faulty associated alleles.
This disease is caused by a mutation on the 12th chromosome, specifically a mutation of the ATXN2 gene. In this gene, there is a specific set of genetic code that repeats in a sequence, labelled “CAG.” These three letters are repeated around 22 times in a healthy individual and up to 32 times. However, in patients with SCA2, this sequence is repeated more than 32 times. Interestingly, the more times that these three letters are repeated, the earlier the onset of the disease is. For example, a person with only 33 repeats of the sequence may experience onset of symptoms in middle or late adulthood, but in a patient who has 40 or more repeats may experience onset as early as young adulthood or even adolescence.
The specific way that SCA2 causes disease can be found in the name of the disease. The condition leads to an attack of nerve fiber endings connected to the spine and cerebellum, hence “spinocerebellar.” The spine and cerebellum (which is a part of the brain) work together to help coordinate practiced movement, which includes walking, speaking, swallowing, and eye movement. By attacking these nerve fibers, the disease leads to impairment of these functions as well as cerebellar degeneration.
Diagnosis
The diagnosis of SCA2 is quite reliable, with genetic testing revealing close to 100% of patients with the condition. The genetic testing specifically looks at the CAG repeats in the ATXN2 gene on the 12th chromosome and can measure the exact number of repeats.
Rarity
There are many types of ataxia, spinocerebellar ataxia being among them. Specifically, SCA2 is a type of spinocerebellar ataxia, and is actually the most common form of the disease. Despite this, it is still extremely rare, with only 1 to 2 cases per 50,000 people.
Treatment
While there is no curative treatment for SCA2, there are many supportive therapies and devices for helping patients cope with their condition. Many of these are lifestyle changes that help to combat the effects of the illness by keeping the body in healthy condition. As such, treatment is aimed at maintaining a patient’s autonomy, and preventing injuries that a person may accumulate as a result of having the condition. Lifestyle changes to keep a healthy weight, including daily physical activity and a healthy, nutritious diet, are often recommended to SCA2 patients. Patients with this illness are also advised to avoid any substances or medications that interfere with cerebellar function, as the cerebellum is the primary organ affected by SCA2.
Supportive devices for both physical support (eg., walking stick/cane, walker,etc.) and communication support (notepads/typing display devices) are often recommended when a person begins struggling with the associated symptoms. Depending on the individual patient’s needs, a drug called Levodopa may be prescribed for movement problems such as muscle rigidity and tremors. Magnesium supplements are also capable of improving cramping if that is a special concern for a patient.
Finding Specialists
Because SCA2 is a rare disease, finding a specialist is very important. Oftentimes physicians treating these patients can have trouble knowing what to expect, so finding professionals who have experience with the disease can be very beneficial. The following link can help you find a specialist: https://rarediseases.info.nih.gov/guides/pages/25/how-to-find-a-disease-specialist.
The NIH and the National Ataxia Foundation also both have many resources with patients with SCA2. The National Ataxia Foundation especially has a list of medical professionals as well as clinics that have special experience in SCA2.
Participating in Research
As we discussed in our research article (click here) research for rare diseases is incredibly important and can offer a lot of benefits to patients. www.clinicaltrials.gov has a list of ongoing trials for SCA2, and can be located using the search bar. CoRDS, or the Coordination of Rare Diseases at Sanford (http://www.sanfordresearch.org/cords/patientsfamilies/), has a patient registry that can link you with researchers. Consult with your physician before coming to a decision regarding clinical trials
For more information on ataxia, visit the National Ataxia Foundation page on the NIH website at: https://rarediseases.info.nih.gov/organizations/44
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Sources:
National Ataxia Foundation. (2008, October). Frequently Asked Questions about Spinocerebellar Ataxia Type 2 (SCA2). Retrieved August 09, 2020, from https://ataxia.org/wp-content/uploads/2017/07/NAF-Web-Content-Publication-SCA2.pdf
Spinocerebellar ataxia 2. (n.d.). Retrieved August 09, 2020, from https://rarediseases.info.nih.gov/diseases/4072/spinocerebellar-ataxia-2
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