Spinocerebellar ataxia type 2 (SCA2) is an inherited neurodegenerative condition that affects the nervous system, with its primary impact on the cerebellum. This part of the brain is responsible for coordinating movement, and as it degenerates, individuals experience a progressive decline in their ability to control movement, maintain balance, and articulate speech. The onset of SCA2 occurs in a person’s thirties, though this can vary, and the condition is characterized by a gradual worsening of symptoms over many years.
Genetic Cause of SCA2
SCA2 is caused by an error in the ATXN2 gene on the 12th chromosome, which holds the blueprint for producing a protein called ataxin-2. In individuals with SCA2, a section of this gene contains a CAG trinucleotide repeat expansion, where the DNA sequence “CAG” is repeated excessively. While everyone has CAG repeats in their ATXN2 gene, typically numbering 22 or 23, the number of these repeats determines whether the gene functions correctly. In SCA2, the number of repeats is 33 or more.
This expansion leads to an altered ataxin-2 protein that is toxic to nerve cells, particularly the Purkinje cells in the cerebellum, causing them to malfunction and degenerate over time. A higher number of repeats is associated with an earlier onset of symptoms and a more rapid progression.
A notable characteristic of SCA2 is “anticipation,” where the number of CAG repeats can increase as the gene is passed to the next generation. This expansion is more likely when inherited from the father, causing subsequent generations to potentially experience an earlier onset and more severe symptoms. SCA2 is inherited in an autosomal dominant pattern, meaning a person only needs to inherit one copy of the mutated gene to develop the disorder. An individual with SCA2 has a 50% chance of passing the altered gene to each of their children.
Progression of Symptoms
The clinical journey of SCA2 is marked by a gradual progression of symptoms that can differ in severity. The most common initial sign is gait ataxia—an unsteady and clumsy walk that is a direct result of damage to the cerebellum. Early on, individuals may also notice slurred or indistinct speech, a condition known as dysarthria, as the muscles for articulation become harder to control.
As the disease advances, a wider array of motor symptoms emerges. One of the features of SCA2 is the development of slow saccadic eye movements, a difficulty in shifting the eyes quickly. To compensate, people often move their entire head to change their line of sight. Other motor issues that can arise include tremors in the hands and painful muscle cramps. Difficulty with swallowing, or dysphagia, is also common and can lead to complications like choking or aspiration pneumonia.
Beyond motor impairments, SCA2 presents non-motor symptoms that impact quality of life. Cognitive changes can occur, often manifesting as problems with executive function, which includes planning, organizing, and memory. Sleep disturbances are another frequent issue, with some individuals experiencing REM sleep behavior disorder. The disease can also affect the peripheral nerves, leading to neuropathy characterized by numbness, weakness, or a loss of reflexes in the hands and feet.
The Diagnostic Journey
Diagnosing spinocerebellar ataxia type 2 begins with a thorough clinical evaluation by a neurologist. This consultation is centered on gathering a detailed personal and family medical history, as a known history of ataxia is a strong indicator. The neurologist will conduct a comprehensive neurological exam to assess coordination, balance, reflexes, and muscle strength, while observing eye movements and speech for characteristic abnormalities.
To rule out other potential causes, brain imaging is often the next step. A Magnetic Resonance Imaging (MRI) scan of the brain is the preferred method. While an MRI cannot definitively diagnose SCA2, it can reveal atrophy, or shrinkage, of the cerebellum and sometimes the brainstem, which supports a suspected diagnosis.
The definitive step is genetic testing. This test analyzes a person’s DNA from a blood or saliva sample to count the number of CAG repeats within the ATXN2 gene. Discovering an expansion of 33 or more repeats confirms the diagnosis of spinocerebellar ataxia type 2. This genetic confirmation can also be used for predictive testing in at-risk family members, though this is undertaken after extensive genetic counseling.
Managing Life with SCA2
While there is no cure to halt or reverse the progression of SCA2, a multidisciplinary approach to management can enhance an individual’s quality of life. This strategy involves a team of healthcare professionals working to maximize independence and maintain function.
Therapy is a primary component of managing SCA2’s physical challenges. Physical therapy helps individuals maintain mobility, improve balance, and preserve muscle strength. Therapists can also recommend and train individuals in the use of assistive devices, such as canes or walkers, to ensure safety and prevent falls.
Occupational therapy focuses on adapting daily living activities. Therapists provide strategies and tools to help with tasks like dressing and eating, and suggest modifications to the home environment to promote safety and independence.
Speech therapy is another component, addressing both communication and swallowing. Therapists work with individuals to manage dysarthria with exercises and communication strategies. They also play a part in managing dysphagia by recommending safer swallowing techniques and appropriate food and liquid consistencies to reduce the risk of aspiration.
Certain medications may be prescribed to manage specific symptoms, such as tremors or muscle cramps, though these do not alter the underlying disease. The journey with SCA2 also involves significant emotional challenges, making support systems valuable. Connecting with support groups allows patients and families to share experiences, while ongoing research into potential treatments offers hope for the future.