Cerebellum (in blue) of the human brain
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Spinocerebellar ataxia

Spinocerebellar ataxia (SCA) is a genetic disease with multiple types, each of which could be considered a disease in its own right. As with other forms of ataxia, SCA results in unsteady and clumsy motion of the body due to a failure of the fine coordination of muscle movements, along with other symptoms. more...

Sabinas brittle hair...
Sacral agenesis
Saethre-Chotzen syndrome
Salla disease
Sandhoff disease
Sanfilippo syndrome
Say Meyer syndrome
Scarlet fever
Schamberg disease...
Schmitt Gillenwater Kelly...
Scimitar syndrome
Selective mutism
Sensorineural hearing loss
Septo-optic dysplasia
Serum sickness
Severe acute respiratory...
Severe combined...
Sezary syndrome
Sheehan syndrome
Short bowel syndrome
Short QT syndrome
Shprintzen syndrome
Shulman-Upshaw syndrome
Shwachman syndrome
Shwachman-Diamond syndrome
Shy-Drager syndrome
Sickle-cell disease
Sickle-cell disease
Sickle-cell disease
Silver-Russell dwarfism
Sipple syndrome
Sjogren's syndrome
Sly syndrome
Smith-Magenis Syndrome
Soft tissue sarcoma
Sotos syndrome
Spasmodic dysphonia
Spasmodic torticollis
Spinal cord injury
Spinal muscular atrophy
Spinal shock
Spinal stenosis
Spinocerebellar ataxia
Splenic-flexure syndrome
Squamous cell carcinoma
St. Anthony's fire
Stein-Leventhal syndrome
Stevens-Johnson syndrome
Stickler syndrome
Stiff man syndrome
Still's disease
Stomach cancer
Strep throat
Strumpell-lorrain disease
Sturge-Weber syndrome
Subacute sclerosing...
Sudden infant death syndrome
Sugarman syndrome
Sweet syndrome
Swimmer's ear
Swyer syndrome
Sydenham's chorea
Syndrome X
Synovial osteochondromatosis
Synovial sarcoma
Systemic carnitine...
Systemic lupus erythematosus
Systemic mastocytosis
Systemic sclerosis

It can be easily misdiagnosed as another neurological condition, such as multiple sclerosis (MS). There is no known cure for this degenerative condition, which lasts for the remainder of the sufferer's life. Treatments are generally limited to softening symptoms, not the disease itself. The condition is irreversible. A person with this disease will usually end up needing to use a wheelchair, and eventually they will need assistance to perform daily tasks. The symptoms of the condition vary with the specific type (there are several), and with the individual patient. Generally, a sufferer retains full mental capacity while they progressively lose physical control over their body until their death.

One means of identifying the disease is with an MRI to view the brain. Once the disease has progressed sufficiently, the cerebellum (a part of the brain) can be seen to have visibly shrunk. The most precise means of identifying SCA, including the specific type, is through DNA analysis. Some, but far from all, types of SCA may be inherited, so a DNA test may be done on the children of a sufferer, to see if they are at risk of developing the condition.

SCA is related to olivopontocerebellar atrophy (OPCA); SCA types 1, 2, and 7 are also types of OPCA. However, not all types of OPCA are types of SCA, and vice versa. This overlapping classification system is both confusing and controversial to some in this field.


The following is a list of some, not all, types of Spinocerebellar ataxia. The first ataxia gene was identified in 1993 for a dominantly inherited type. It was called “Spinocerebellar ataxia type 1" (SCA1). Subsequently, as additional dominant genes were found they were called SCA2, SCA3, etc. Usually, the "type" number of "SCA" refers to the order in which the gene was found. At this time, there are at least 22 different gene mutations which have been found (not all listed).

Identifying the different types of SCA now requires knowledge of the normal genetic code, and faults in this code, which are contained in a person's DNA (Deoxyribonucleic acid). The "CAG" mentioned below is one of many three-letter sequences that makes up the genetic code, this specific one coding the aminoacid glutamine. Thus, those ataxias with poly CAG expansions, along with several other neurodegenerative diseases resulting from a poly CAG expansion, are referred to as polyglutamine diseases.


Both onset of initial symptoms and duration of disease can be subject to variation. If the disease is caused by a polyglutamine trinucleotide repeat CAG expansion, a longer expansion will lead to an earlier onset and a more radical progression of clinical symptoms, resulting in earlier death.

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From Medicine and Health Rhode Island, 5/1/04 by Friedman, Joseph H

I recently stumbled on an interesting ethical issue in the course of a rather benign and relatively uninspired research endeavor. I am fascinated by the ethical question as well as the surprising and unexpected fashion in which it occurred. I was listening to a patient with an inherited disorder who, after about 10 years of seeing me, mentioned a sleep problem he'd had for over a decade. I thought it had never been reported in this disorder so I started asking my other patients with the disease if they had this problem too, and to and behold, I was onto something.

There are now a host of inherited disease which can be tested for. The most common two that I deal with are Huntington's disease and Machado Joseph disease, also known as spinocerebellar ataxia type 3 (SCA 3). Both are autosomal dominant disorders with 100% penetrance, meaning that those who carry the affected gene will get the disease if they live long enough. Both diseases are "CAG trinucleotide repeat" disorders, also known as "polyglutamine" disorders, meaning that the gene for the affected protein which normally contains many CAG nucleotide repetitions, each of which co des for the amino acid glutamine, is disordered when it contains an excess number of repeats. This means that the protein coded for then contains more glutamine amino acids than it should, which causes the protein to fold abnormally, which in some manner, causes certain brain cells to die. There is a threshold number of repeats below which the gene is normal, above which the gene brings disease. The onset of the disease relates inversely to the number of tripler repeats. The greater the number of repeats, the earlier the disease onset is, in general. But this correlation is not specific, so that some people with 50 repeats may develop the disease at age 30 while others develop it at age 50. There is a definite correlation, however, that is fairly strong for large numbers of patients, but which does not correlate with each individual. Both diseases can be tested for with commercially available genetic tests. Thus an at-risk individual can be tested for the disease, learn that he/she has an abnormal gene but will not know when the disease will begin. Very few at-risk individuals choose to be tested for the gene since both diseases are untreatable. Mostly the testing is done for reproduction decision-making. Most people at risk for both diseases prefer to remain ignorant of their gene status, preferring the sword of Damocles to the certainty of a laboratory test.

Before the genes were identified, researchers had attempted to find tests that might distinguish those destined to develop the disease from those who would be spared. No tests were found for either illness, and commercially available gene testing now makes other tests superfluous. However, recent clinical discoveries suggest that "premonitory" or "herald" signs may predate the presumed disease onset by 10 years or more. If true it would mean that the clinical disease onset is actually the date at which the "premonitory" symptom first appears. Let me be explicit. It appears, but is not yet certain, that SCA 3 has a high incidence of REM sleep behavior disorder (RBD) (an interesting topic for another column). This is a 2003 observation, unknown yet to people with the disease. RBD is a very rare sleep disorder outside of people having Parkinsonism or SCA 3. Some SCA 3 cases have been reported in which the RBD appeared more than 10 years before any of the "standard" symptoms of SCA 3 began, namely ataxia, eye movement abnormalities, or neuropathic symptoms. If RBD is truly part of the SCA 3 syndrome, then the occurrence of RBD in an at-risk individual, that is an individual who has a parent with SCA 3 and therefore has a 50% chance of having the abnormal gene, strongly suggests that it is the herald symptom of the disease since RBD is extremely rare outside the context of SCA 3 and parkinsonism. This observation, if true, means that if an SCA 3-at risk person develops RBD it becomes more than an interesting and perplexing sleep disorder. It becomes a disease-defining event even though the person is in every test-able fashion normal. If this hypothesis is proven, and the information becomes known among the SCA 3 community, as it certainly will, then we will have removed some of the population's "right" to remain ignorant, their "right not to know."

I view this as an ethical problem. If establishing the connection between RBD and SCA 3, when there is no treatment available, overrules the vast majority of the at-risk population's decision to not be tested for the gene, hence their conscious decision to remain ignorant, I will be countermanding their decision. I will be involved in overriding their decision by pointing out a clinical connection not widely known, and not proven. Do I have the "right" to trump this decision? Of course, publishing my observations and now, this column, indicate that I have so far opted on the side of public knowledge, but the next step, to "prove" the connection has not been planned.

The day I stumbled on this problem I had the amazingly good fortune, (synchronicity, jung would say) to see an intelligent, thoughtful and articulate young woman at risk for SCA 3, who came to be tested for the gene abnormality. Without telling her what clinical syndrome I thought I had linked to SCA 3, I outlined the general problem and asked her for her opinion. She immediately slated that the conncerion had to be investigated and proven, if correct. Any information, she said, that shed light on the disease, no matter where it led, had to be explored since no one knew where it would lead. She had no iota of doubt and thought the "protection" from "knowledge" position was an argument without merit.

I am unsure she is correct. I think she is. I am not hiding my observation and, together with an ethicist we have raised the question in a neurology journal and look forward to our colleagues' input. While I'm unsure there is a "correct" response to many ethical questions, I strongly think that the wider the discussion, the better it will be for the medical community, and hopefully for those at risk as well. This is new territory for me, and, I suspect, for many of my colleagues, but will become increasingly common in the near future.


Copyright Rhode Island Medical Society May 2004
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