Spinocerebellar ataxia (SCA) is a degenerative, progressive, genetic/hereditary, and often fatal disorder. It refers to a group of hereditary diseases, ataxias in particular, that are defined by degenerative changes in the spinal cord, basal ganglia, retina, spinal tract, and in the cerebellum, the part of the brain that has something to do with motion control,
that can affect speech, coordination, and balance. SCA may be a result of either a dominant or a recessive gene. It is sometimes called spinocerebellar degeneration or spinocerebellar atrophy.
SCA has multiple types which are grouped according to the mutated gene that is liable for the particular type of SCA and is all defined by autosomal dominant inheritance. Each type could be considered a disease in its own right. The different types of SCA are named with the acronym SCA and then the number according to the order of their discovery, ie. SCA 1, SCA 2, etc. All types of SCA are defined by a progressive difficulty in walking and are often linked with impaired speech and poor coordination of eye movements and hand movements.
SCA may affect anyone of any age. SCAs exhibit slow progression of the pancerebellar dysfunction that usually begins at childhood and is differentiated by the involvement of other nervous systems. The onset of symptoms for SCA is usually visible after the age of 18 for the adult-onset. There are some types of SCA that have a childhood-onset but SCA is more common in adult-onset. Since SCA is gradually progressive, the symptoms of this condition worsen little by little over a period of years although there are some types of SCA that can progress more quickly and rapidly compared to the others.
The MRI and CT scans of individuals with SCA show atrophy or shrinkage of the cerebellum and it becomes more noticeable as the disease progresses.
The symptoms of SCA may vary depending on the specific type of SCA and on the individual. An individual with SCA retains full mental capacity but slowly loses physical control.
SCA affects 1 to 4 out of 100,000 people.
Spinocerebellar ataxia is caused by mutations in various genes that are needed for normal functioning of the brain. For some types of SCA, the genes that are known to cause it have already been determined while the genetic cause might still be unknown in other types of SCA.
SCA usually has genetic causes and the inheritance is autosomal dominant but the specific causes vary depending on the type of SCA.
Trinucleotide repeat expansions cause most types of SCA obtained in an autosomal dominant fashion. Trinucleotide repeat refers to a repeated segment of DNA for a number of times. These repeats normally exist without causing any problems but if these repeats go beyond the normal or accepted number of repeats, there is a possibility for them to interfere with the normal function of the protein made by the gene and cause a genetic disease. Trinucleotide repeats are not stable and its length can change when passed on from a parent to his/her child. An incline in the number of repeats results in an early age onset of SCA and more serious conditions.
A singular mutated copy of the gene at fault for SCA in each cell is more than enough to produce signs and symptoms of SCA for autosomal dominant conditions. This means that the each of the children of an individual with the autosomal dominant condition has a 50% chance of inheriting the mutated copy of the gene from the affected parent.
Some types of SCA are caused by sequence changes in the genes or deletions of some genes. A genetic change such as a large duplication of a piece of genetic code can also lead to SCA.
The cause for many types of SCA still haven’t been identified or discovered until now.
Spinocerebellar ataxia has different symptoms depending on the type of SCA and the individual. Each type of SCA manifests different symptoms and this is usually what distinguishes one from the other.
Since SCA is a progressive disease, some symptoms may manifest as early as childhood while some may occur in late adulthood.
- Problems with walking
- Difficulty in coordinating hand movements
- Paralysis of eye movements
- Reduced reflexes
- Abnormal eye movements
- Various forms of nystagmus
- Slow saccades
- Hypermetric saccades
- Diminished velocity saccades
- Positional vertigo
- Slow eye movements
- Loss of vision
- Ataxia or Coordination issues
- Difficulties with walking
- Speech difficulties
- Unsteady or uncoordinated walk
- Poor coordination
- Food regurgitation in mouth
- Muscle stiffness
- Cognitive impairment
- Tingling or pain in the arms and legs
- Uncontrolled muscle tensing
- Muscle wasting
- Muscle twitches
- Involuntary jerking movements
- Problems with balance
- Stiff muscles
- Twitching movements in the face and tongue
- Difficulty with coordinating arms and legs
- Peripheral neuropathy
- Migraine headache
- Episodic disorder
- Decreased visual acuity
- Decreased color vision
- Similar symptoms of Parkinson’s disease
- Similar symptoms of multiple sclerosis
- Mood disorders
Clinical evaluation involving an extensive neurological examination is one way of diagnosing spinocerebellar ataxia. In the clinical evaluation, a clinical algorithm is used.
If the patient presents symptoms of spinocerebellar ataxia after thorough and detailed physical examination, other organ systems are also checked. An ophthalmological examination may also be advised based on the symptoms and examination.
The doctor also obtains a three-generation family history and examines other members of the family most especially the parents.
A CT scan or an MRI scan has the potential to detect degeneration of the brainstem and the cerebellum, a common finding in people with SCA. The involvement of other parts of the neuraxis is also checked for involvement during an MRI scan.
The best way to verify if a person has SCA is through genetic testing. It can determine the specific type of SCA that a person has. Genetic testing is used to test the various genes that are known to cause SCA. Carrier testing on the other hand for the relatives who are at risk of having SCA. Prenatal testing is done if the mutations causing SCA in the family are known or identified.
Genetic testing is done to discover whether an individual has inherited the repeat expansion or gene mutation for SCA or not. This testing is done for SCA types 1, 2, 3, 6, 7, 8, 10, 12, 14, and 17 which are the types of SCA that are caused by a repeat expansion. Blood samples or tissue samples can be used for the genetic testing. If the type of genetic SCA is already known in the family, only that specific type of SCA will be tested for.
Testing is done for SCA types 1, 2, 3, 6, and 7 if the type of SCA has not been determined in an affected person or a family. The results of the SCA testing comes out after 2 to 4 weeks.
Symptomatic testing is done to determine the cause of ataxia in an affected individual while presymptomatic testing is done for an individual who is at risk of having SCA but does not show any signs or symptoms of the condition.
It is really important to confirm the diagnosis and type of SCA within the family.
Medical records on affected family members are often requested.
The results of the genetic testing may either be normal/negative, positive, or uncertain.
A person may still be affected with SCA despite a negative result in the genetic testing.
There is no specific cure for spinocerebellar ataxia at the moment considering that it is a progressive and irreversible disease. The treatments available are more for relieving the symptoms. However, there have been studies in finding a potential cure for SCA.
The best treatment for SCA is different per SCA type and they also depend on the manifested signs and symptoms of an affected individual.
If the ataxia is caused by underlying conditions, the individual undergoes treatment to cure the underlying condition. For example, if the ataxia is a result of a metabolic disorder, the patient is treated with medications and a controlled diet. Vitamin therapy is for a patient that has a vitamin deficiency.
There are also a couple of medications to lessen the symptoms and treat gait and swallowing disorders. Muscle relaxants are used to relax the muscles that are contracting and are causing pain. Acetazolamide (Diamox) or topiramate (Topamax) may help in the episodic phase of the SCA6. Zolpidem improves the symptoms for SCA2. Varenicline improves symptoms for SCA3.
Physical therapy is recommended to help in strengthening their muscles and to train the uncoordinating muscles. With therapeutic exercise programs, physical therapists are able to help patients maintain their level of independence.
Speech therapy is done on patients who are suffering from speech difficulties to improve the use of muscles in speaking. Speech-language pathologists may use alternative and augmentative communication devices or behavioral intervention strategies to help patients with impaired speech.
Assistive technologies and other therapies are also recommended to help affected individuals in their daily activities. Occupational therapy is done on patients so that they can learn to modify some of the motor functions through the use of adaptive devices.
A walker or a cane is advised for patients who have a tendency to fall.
Psychological counseling is also recommended but it depends on the patient, the patient’s family, and their specific needs.