Spinocerebellar ataxia

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.

JOSEPH H. FRIEDMAN, MD

Copyright Rhode Island Medical Society May 2004
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