Short answer: yes.

Longer answer:
SCA is a group of genetic diseases, not a single thing, and a problem with any one of several different genes can be the underlying cause.

This gets quite tricky. A lot of the genes have altered function that leads to disease as a result in the transgeneration expansion of a slightly unstable part of the gene, called a triplet repeat. With many of these sorts of disease (Huntington is the archetype I guess), it can suddenly appear with no prior family history, just because in the current generation, the expansion has reached sufficient length to interfere with gene transcription or the function of the encoded protein.

For other of the genes, a simpler mutation scheme operates, and here there is more likely to be a family history. However, new mutations can and do occur, so even in the absense of such a history, the disease would still be considered genetic.
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P.S.

I see wikipedia has an article on this that lists a lot of the genes that could be involved.
http://en.wikipedia.org/wiki/Spinocerebellar_ataxia


Edited by xarqi on October 26 2005 at 10:18 PM

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Hmmmm.

I'll give you a quick answer and then do some digging and get back to you.

For the "usual" mutation mechanism, yes. Environmental mutagens could cause a new mutation that could disrupt a copy of the gene. (I need to check to see if the mode of inheritance is dominant or recessive to be clearer on this, and that too may depend on the particular gene.

For the triplet repeat genes, not much is known about what causes the slippage during DNA replication. I guess there is scope for environmental factors here too, but I can't say for sure).

I'll get back with more when I've done some digging.


Edited by xarqi on October 26 2005 at 10:58 PM

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OK - Maureen has kindly re-opened this question for me so I can provide the additional information I promised. I've already sent this to you via Private Message, but here it is in case you don't have PM notification turned on.
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The OMIM database is THE place where human genetics information is stored. I jumped in there to see what I could find about SCA.

Here are some of the links:
(Main entry is the first one)
SCA1: http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=164400
SCA4: http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=600223
SCA7: http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=164500
SCA19/22: http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=607346

You can easily find the other ones by searching OMIM using "spinocerebellar ataxia"

Inheritance is autosomal dominant. That means if you inherit one bad copy of a gene, you get the disease. It also means that if either the ovum or sperm that went to create you suffers a mutation that creates a "disease" version of the gene, then you will get it too, and so will half of your children on average. My educated guess would be that most of the mutations seen would be frame-shifts, where only a single DNA base is inserted or deleted, but the whole structure of the resulting protein changes from that point on. That could occur in either the "normal" type genes or the ones that are susceptible to triplet instability.

It IS a big subject, sorry.

As for environmental factors, it is much as I said. Things like free radicals, and radiation can cause frame-shift mutations. These would occur in the gametes (egg/sperm) carried by the parents, and only show a problem after conception - or in the case of SCA - in adult life. Also, there is not much on the influence of environmental factors on triplet instability, but take a look at this recent paper:
http://hmg.oxfordjournals.org/cgi/content/full/6/12/2005

I hope that helps.

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