The spinocerebellum is an area of the brain which is connected to the spinal cord and controls a person's motor abilities.

This is an image of the cerebellum:



Fig. 1: An image of the cerebellum

Source: http://depts.washington.edu/neurogen/downloads/ataxia.pdf

As you can see, the cerebellum is located at the back of the brain, so it's not very likely that it will be damaged. In the case that it is damaged (for instance, through a brain injury or stroke), a person will feel uncoordinated and awkward because the cerebellum controls balance and the coordination of movements.

Ataxia is a symptom where a patient is unable to control his or her movements in a normal and comfortable manner. For instance, they might find it hard to balance when standing up or move their hands in a steadily.

Another name for this disease is "spinocerebellar degeneration" because it is triggered by the degeneration of the brain.

Now compare these the two images below:



Fig. 2: Two MRI scans. The cerebellum of the brain on the left shows signs of degeneration while the cerebellum on the right is healthy.

Source: http://depts.washington.edu/neurogen/downloads/ataxia.pdf

And here are two other interesting images to take a look at:

Fig. 3 - MRI scan shows the degeneration of the cerebellum

Source: http://www.marmaramedicaljournal.org/pdf/pdf_MMJ_399.pdf



Fig. 4 - MRI scan shows the degeneration of the cerebellum

Source: http://www.marmaramedicaljournal.org/pdf/pdf_MMJ_399.pdf

In the MRI or CT scans (these are both brain scans, like the image above) of many spinocerebellar ataxia patients, there is a indication that their cerebellum is shrinking and/ or breaking down.

Of course, the extent to which the cerebellum has deteriorated depends on the onset of the disease. SPA (Spinocerebellar ataxia - I will be using this short form a lot) is a slow and progressive disease, which means that the symptoms will worsen over a long period of time. However, there are many types of SPA, some which can progress faster than others.

This disease rarely appears in children under 18, with the majority of patients being well into their 20s, 30s, and 40s.

In the next post, I'll explain some of the symptoms of SCA.

The following is a list of symptoms that someone with SCA might experience:

1. Speech impairment: difficulty in speaking clearly and smoothly, especially when trying to pronounce consonants (dysarthria)
2. Difficulty hearing
2. Disease could affect the spine and cause the patient to slouch
3. Short and sponteneous spasms of movement
4. Inability to coordinate legs, especially when trying to walk (this comes hand in hand with inability to control other movements in the body such as hand movements)
6. Loss of balance, frequent falling
7. Uncoordinated eye movements (nystagmus is uncontrolled, rapid eye movements)
8. Clumsiness
9. Rapid weight loss, muscles shrink and lose strength
10. Could lead to paralysis
11. Constant shaking in hands
12. Dizziness
13. Problems swallowing food (often choking)

Furthermore, there might be "side effects" of having SCA, such as depression which is not directly linked to the disease itself, but will also have a big impact on a person.

Although this list will probably freak some people out, not all of these symptoms will appear at the same time. As I talked about in my previous post, SCA is a gradual disease and it might take several years after the onset of the disease for some symptoms to even show.

One good thing is that the cognitive sense of an SCA patient are normal because the area of the brain that controls mental abilities is not affected by SCA.

Spinocerebellar ataxia is a hereditary disease. It genetically passed from affected parent to a child. This disease is autosomal dominant, meaning that approximately half of the children will inherit the disease if at least one of the parents is affected. This can be seen below:



Fig. 5: Autosomal inheritance of SCA

Source: http://depts.washington.edu/neurogen/downloads/ataxia.pdf

This can also be seen by drawing a dichotomous key (please click to zoom in):



Fig. 6: A dichotomous key showing the autosomal inheritance of SCA

Source: No source

Although there are many different types of spinocerebellar ataxia (more information about the different types of SCA here), each with their distinct characteristics, all types are caused by a mutation in a certain gene which controls activity in the brain.

Fig. 7 - CAG repeat expansion

Source: http://depts.washington.edu/neurogen/downloads/ataxia.pdf

One particular mutation occurs in SCA types 1, 2, 3, 6, 7, and 12 and it's called a CAG repeat expansion. CAG, a part of the DNA sequences that codes for the protein glutamine, is repeated more than is normal, which then affects the proteins which it codes for.

In SCA type 8 and 10, the CTG and ATTCT pattern is repeated too many times respectively, while in type 14, a different sort of mutation (point mutation) occurs in the PRKCG gene. A point mutation occurs when a single nucleotide base is altered, added, or removed in a normal DNA sequence.

Some individuals who inherit the SCA gene with a repeat expansion actually don't show any symptoms in their lifetime. This is known as non-penetrance and is a very rare phenomenon. Researchers are still trying to find the cause of this.

Currently, there are 25 known types of SCA although there are probably others which just haven't been discovered yet. Here is a table which shows the 11 most common types (there is no ataxia #9).

Please click to zoom in:



Fig. 8 - The 11 most common types of SCA

Source: http://depts.washington.edu/neurogen/downloads/ataxia.pdf

Please be aware that numbers are not assigned to a certain type of SCA depending on the severity of the disease, but by the order in which each type was discovered.

Each type has its own characteristics such as symptoms or onset of disease. Sometimes, however, the characteristics may overlap, in which case genetic testing may be required. Currently, there is only genetic testing available for SCA types 1, 2, 3, 6, 7, 8, 10, 12, 14 and 17.

A distinct phenomenon which occurs in SCA types 1, 2, 3, and 7 is called anticipation. This means that the severity of the disease will increase with each new generation. That means the affected offspring of a person with SCA is likely to experience more severe symptoms than his/ her parent. The onset of the disease will also be earlier in the child than the parent. Later, I will show a case study which has a good example of anticipation to demonstrate how it works.

The following study was performed on a Turkish family with a history of SCA type 2.

The first patient (II.2) is a 49 year old female. During her 40s, she began to experience symptoms of SCA. Initial signs included disequilibrium (loss of balance) and dysarthria (difficulty in speech). Her condition continued to worsen and within two years, she was having trouble controlling her hand movements. Testing showed abnormalities in her eye/ limb movements and gait and an MRI scan confirmed that these symptoms were caused by cerebellar atrophy, or the shrinking of the cerebellum. However, her cognitive senses appeared to be fine after she received a score of 29/30 on her minimental status test (a test used to detect for any cognitive impairment).

Her brother (II.3), who was 47 years of age at that time, also began experiencing disequilibrium in his 40s.


Their mother (1.4) has similar symptoms, but the onset of the disease did not appear until she was in her 60s. She also has a case of explosive speech, which is loud and sudden talking that cannot be controlled.


The son of the first patient (111.1) began to experience symptoms when he was only in his 20s. At first, he had head titubations. This later progressed to more severe symptoms, similar to the ones that his mother had experienced: dysarthria, eye and limb movement impairments. MRI testing revealed that he also had cerebellar atrophy.

Fig. 9 - Pedigree which shows the family history of the four patients mentioned above

Source: http://www.marmaramedicaljournal.org/pdf/pdf_MMJ_399.pdf

Fig. 9 shows the inheritance of SCA in this family. We can see that the disease is autosomal dominant because of three good indicators:

a) the disease appears in each generation

b) the disease seems to affects males and females equally

c) the disease affects approximately half of the children

This case study is a good example of anticipation, which was explained in an earlier post. In this family, the onset of the disease did not appear in the parent generation until she was in her 60s. However, the F1 generation experienced symptoms when they were in their 40s, and in the F2 generation had developed symptoms by the time he was only in his 20s. From this, we can conclude that there is a general trend: with each new generation, the disease appears at an earlier age than in the previous generation.

Although there is currently no cure, there are many ways to improve the condition of a patient with SCA and assist them in performing everyday tasks.

1. A patient with SCA is encouraged to exercise, which helps them maintain control over their motor skills and slows the wasting away of muscle strength to a certain degree.

2. There are physical, speech, and occupational therapists available for patients with SCA.

Physical therapists: Assist the patient with exercising.

Speech therapists: Assist the patient with swallowing, coughing, and speaking. Can recommend communication aids.

Occupational therapists: Assist the patient with everyday tasks, such as eating and dressing. Can recommend transportation devices, such as wheelchairs, or make other adjusments which they think would help a patient.

2. Certain adjustments such as wearing protective clothing or using railings when walking up stairs can help a patient who is prone to falling down. Cutting food into little pieces can help a patient who has trouble swallowing. There are many small changes which might seem insignificant but will greatly reduce the problems for a person with SCA.

3. Wheelchairs and computers are invaluable for patients who have lost the ability to walk or communicate.

4. Although there is no cure for SCA itself, it's possible to treat certain symptoms of the disease. For example, there is medicine called baclofen which is used to treat muscle spasms.

5. There are many counselling services and support groups for people with SCA.