I know exactly what kind of hereditary ataxia that I have, but some questions have been nagging me recently:
I have spinocerebellar ataxia (SCA), and I know this is causing my cerebellum to degenerate. But why is it called spinocerebellar ataxia? Is my spine involved in the disease? Does my spine or rather the neurons throughout my body also degenerate?
Is it ever correct to refer to spinocerebellar ataxia as simply cerebellar ataxia?
Things are never simple
If things were simple, then I would say yes, I have ataxia; yes, I have cerebellar ataxia; yes, I have spinocerebellar ataxia; and, yes, I have spinocerebellar ataxia type 3. But things aren’t quite that simple.
To make matters a bit more complex, the term ADCA (autosomal dominant cerebellar ataxia) Type I is defined as a container term for a number of different SCA versions. I have SCA3, therefore I have ADCA Type I.
https://ojrd.biomedcentral.com/articles/10.1186/1750-1172-6-33
Autosomal dominant cerebellar ataxia = a certain set of neurological signs that go beyond pure cerebellar issues and beyond ataxia as a symptom = spinocerebellar ataxia
In other words, if you have cerebellar ataxia due to an autosomal dominant defect, then you have spinocerebellar ataxia. ADCA Type I comprises various SCA types, so its list of “other neurological signs” is lengthy and all-inclusive. Keep reading for more specifics.
Note that SCA is autosomal dominant. SCAR is autosomal recessive. SCAR is not a type of SCA.
A bottom line so far
The dominant hereditary ataxias that have spinocerebellar in their official monikers should not be shortened to cerebellar ataxia (CA). If you have SCA and refer to your kind of ataxia only as cerebellar, it will sound a bit like you are unsure of its genetic nature, or of its type in general.
I don’t think cerebellar ataxia refers to a concrete disease. It’s more of a descriptive term that is non-specific to us with SCA, as well as a symptom of specific diseases other than the diseases in the ataxia family—e.g., multiple sclerosis.
A treasure trove
There’s a treasure trove of information here:
In the introduction, only cerebellar ataxia is described, which does not involve the spinal cord (but then, why would it?).
The specifics brought out by the spino are in “Table 5: Associated features in differential diagnosis of the dominantly inherited ataxias.” For example, with SCA3, there’s:
- Nystagmus
- Spasticity
- Neuropathy (peripheral neuropathy)
- Basal ganglia features
- Eyelid retraction
- Facial fasciculations (twitches).
“Associated features” seem to be called “non-ataxia signs” elsewhere. These are the symptoms of SCA that go beyond ataxia as a symptom. Bear in mind—the use of the word ataxia is overloaded here. Ataxia (i.e., lack of coordination) is a symptom of a variety of diseases and conditions (e.g., being drunk), and not just a symptom of the family of diseases with ataxia in their name. Again, the ataxia family of diseases have many issues that go beyond ataxia as a symptom, and these are called non-ataxia signs.
INAS: http://www.ataxia-study-group.net/html/about/ataxiascales/inas/Inventory-of-Non-Ataxia-Signs.pdf
Table 6 (in the treasure trove) seems to also be a compendium of issues specific to different types of SCA. For SCA3, we have:
- Brainstem involvement
- Pyramidal involvement (nerve fibers that control voluntary movement)
- Extrapyramidal involvement (nerve fibers that control involuntary movement)
- Hyperreflexia
- Peripheral nerve involvement
- Supratentorial features
- Ocular features
In other words, there’s heavy involvement of the spine and spinal tract (i.e., the nerves that travel throughout the body and are used for coordinated movement and peripheral sensation).
However, importantly, I haven’t gotten to the bottom of whether the polyQ feature of SCA3 causes neurons outside of the cerebellum to degenerate and die. My informal conclusion is that the answer is “no,” that the cerebellar degeneration causes only data-processing failures with data traveling along the spine to and from the cerebellum. Ultimately, that can lead to mechanical failures throughout the body, but the cause is neuronal degeneration in the cerebellum and not neuronal degeneration throughout the body.
In other words, my conclusion is that the word spinocerebellar is fraught with difficulty as far as precise meanings go. Though the spine and the cerebellum are both affected, the spine is involved, whereas the cerebellum degenerates. More:
Another trinity arises
The cerebellum comprises three functional areas: the vestibulocerebellum, the spinocerebellum, and the cerebrocerebellum:
https://en.wikipedia.org/wiki/Anatomy_of_the_cerebellum#Phylogenetic_and_functional_divisions
This seems to answer one question: the spinocerebellum refers to the part of the cerebellum that takes data from the spine (the spinocerebellar tract) and processes it. I wanted to conclude that the degeneration that occurs due to SCA does not occur in the spine but in the data processing that occurs in the spinocerebellum, hence the adjective spinocerebellar.
But once again, things are not that simple. First, it’s obvious to me that SCA3 affects all functional areas of the cerebellum and not just the spinocerebellum. Second, there’s this:
Here’s a twist
Here’s a look at things using the Google Ngram Viewer, though the danger is that Google sometimes picks up the ‘published by, since’ date as the ‘publication date,’ which can differ by well over 100 years. Also, note that Mendelian inheritance wasn’t proposed until 1865.
- 1851 is the earliest reference I see to cerebellar ataxia.
- 1877 is the earliest reference I see to hereditary ataxia.
- 1903 is the earliest reference I see to spinocerebellar.
- 1903 is the earliest reference I see to spinocerebellar ataxia.
- The terms ‘hereditary ataxia’ and ‘spinocerebellar ataxia’ compared.
- 1959 is the earliest reference I see to spinocerebellum.
- 1973 is the earliest reference I see to Machado-Joseph disease.
I erroneously assumed that SCA was named in the 1990s when the specific genetic defects were uncovered. I had no idea the term and the disease(s) had been known about for over 100 years now.
Also, the lateness and sparse usage of spinocerebellum leads me to confirm that spinocerebellar is not the adjectival form of spinocerebellum after all.
SCA3 vs. MJD
SCA3 and MJD (Machado-Joseph disease) refer to exactly the same disease. The MJD moniker was assigned in 1972. The SCA3 genetic defect was identified about 22 years later (and a genetic test was developed). Hereditary ataxia and MJD were thought to be two different diseases until then.
The naming of the disease in 1972 has led to some mythology, specifically that the disease recently started in the Azores (a group of islands in the Mid-Atlantic Ocean, belonging to Portugal) and contaminated the world with a new disease. Not so. Many in support groups trace their ancestry to the Azores, think they have found the origins of SCA3 in their family, and stop there. But it was only named after studying people there with a high disease prevalence. The disease proliferated disproportionately there but it did not start there. It’s had hundreds of years to develop worldwide and pool disproportionately there.
I prefer referring to my disease as SCA3, or simply as ataxia. As SCA3, it sounds orderly and methodical. It puts it in its place with the dozens of other SCAs and avoids sounding unique. Also, whereas I see no hope of society learning about the term MJD, I’d say there is the offhand chance of society becoming familiar with the term ataxia, similar to its familiarity with the names Parkinson’s disease and Alzheimer’s disease (and others).
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