Talk:Trinucleotide repeat disorder

Other lengths

According to my genetics text-book (Thompson & Thomspons, Genetics in Medicine, 2007 pg 388): "...other disorders have now been found to result from the expansion of longer repeats; these include a tetranucleotide (CCTG) in myotonic dystrophy 2 (a close genocopy of myotonic dystrophy 1) and a pentanucleotide (ATTCT) in the spinocerebellar atrophy 10)." So it doesn't just have to be three base pairs. —Preceding unsigned comment added by 151.197.226.243 (talk) 01:03, 9 September 2007 (UTC)

Tetra and penta nucleotide repeat disorders would by definition not be trinucleotide repeat disorders. Friedreich's ataxia is an even longer repeat unit derived from an alu repeat I think.

You are correct that DM2 and SCA10 are caused by expansion of non-triplet repeats. This is why many scientists in the field are now referring to these diseases as "repeat expansion diseases". (which suggests to me that the title of this article should be modified).

DM2 is caused by an expanded CCTG repeat (http://www.sciencemag.org/cgi/content/full/293/5531/864) (http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=15065017)

SCA10 is caused by an expanded ATTCT repeat (http://www.neurology.org/cgi/content/abstract/67/4/607) (http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=15127363)

By the way, Friedreich's Ataxia (FA) is caused by an expanded GAA repeat that lies within an Alu element (Alu-Sx family) in intron 1 of the frataxin gene. But the disease-causing expansion is still a trinucleotide repeat expansion of the GAA repeats that lie in the middle of the Alu element. It's a bit annoying/confusing because Alu elements are also referred to as "Alu repeats". So there's a GAA repeat inside the "Alu repeat". But it's only the GAA repeat that is expanded. To make matters worse, the Alu element that contains GAA repeats is sometimes referred to as a "GAA-Alu element". Anyway, the important thing is that FA is caused by an intronic GAA expansion. (http://archneur.ama-assn.org/cgi/content/abstract/65/10/1296) (http://www.fasebj.org/cgi/content/abstract/22/6/1625)

P.S. I tried to provide references above that are available as "Free Text" versions from journals who don't require an online subscription. Hopefully they'll show up as free for you, too (if you feel like reading them, or you might find them too detailed and/or boring...)

Beth L Rogers (talk) 02:23, 23 July 2009 (UTC)

Just a thought, this page could maybe do with some more clarification. Tri nucleotide repeat disorders are implied in the article to occur 'in the gene' coding for the disease related protein. More specifically, its in the promoter region of a gene where this tri-nucleotide repeat occurs. The sequence of the repeat itself isnt usually relevant, except for the fact it contains CpG sequences susceptible to methylation. Methylation of long repeated strands of these repeats causes silencing of the gene, and the associated disease. —Preceding unsigned comment added by 87.194.219.186 (talk) 16:26, 19 October 2007 (UTC)

It isn't always in the promotor region, it's more often in the coding sequence, eg, polyGln disorders. It also doesn't often result in methylation of CpG islands. What you are describing sounds most like how fragile X syndrome works but that isn't a universal mechanism for triplet repeat disorders.

Non-viable di/tetra repeats

Explanation for increased viability of trinucleotide repeats compared to di/tetra repeats lies in that tri nucleotide repeats' extension and contraction does NOT cause FRAMESHIFT while other do. —Preceding unsigned comment added by 89.1.40.121 (talk) 00:54, 10 March 2008 (UTC)

Removed statement that trinucleotide repeat disorders are inherited in "non-mendelian" manner

Trinucleotide disorders, such as Huntington's disease, can be inherited in a mendelian pattern. Fragile X is definitely non-mendelian, but with Huntingonton's it's more complicated. Huntington's can be non-mendelian or mendelian inheritance b/c the repeats can expand during cell cycles, and cross a threshold from silent phenotype to dominant inheritance. So, it's not exactly mendelian, but calling it "non-mendelian" will be confusing to readers without a background in genetics. It would be especially confusing since, in clinical terms, once a disease like Huntington's appears in a family, it will continue to be inherited in a mendelian, autosomal dominant way. So, repeat disease can be mendelian or non-mendelian, depending on the case. Maybe we can work on explaining this, but it might be beyond the scope of the article. Also, the citation for the sentence didn't state that trincleotide repeat disorders are non-mendelian. Txh190 (talk) 1:59, 20 June 2008 (UTC)

In the case of repeat expansion diseases, the term "non-Mendelian" is meant to refer to the fact that there is not a 1-to-1 transmission of the exact same mutation from parent to child. The mutation is in the same gene, and the probabilities of inheriting an abnormal number of repeats still follow Mendelian rules. But because the mutation itself has changed somewhat (i.e. the number of repeats has changed), scientists in the field often refer to this as non-Mendelian inheritance. And the phenomenon of "genetic anticipation" inherent with these diseases adds another level of complication to the inheritance pattern. A parent can have a larger-than-normal number of repeats, but not enough repeats to cause the disease (this is a pre-mutation allele). But when the number of repeats increases in the next generation, the disease seems to suddenly appear in this family, even though the expanded repeat may have been in the family for a generation or two before it became large enough to be a disease-causing allele. The main point is that these are a very unique class of mutations that do not perfectly fit the classical rules of Mendelian inheritance. I can see how the term "non-Mendelian" can be confusing, and technically it's still not a completely accurate term, but we still use it when referring to the repeat expansion diseases. My suggestion would be to put back the mention of "non-Mendelian" inheritance (since it is a commonly used term in the scientific literature when referring to these diseases) but explain what is meant by this term in the context of this special class of mutations. Beth L Rogers (talk) 02:57, 23 July 2009 (UTC)

Free full text article

Just found this article on polyglutamine aggregation: http://hmg.oxfordjournals.org/cgi/content/full/12/suppl_2/R173. LeeVJ (talk) 11:56, 1 September 2008 (UTC)

ANd this one covers SCA1 to SCA28 and 16q22-linked SCA, ataxia with vitamin E deficiency (AVED), ataxia with oculomotor apraxia type 1 (AOA1), DRPLA, Friedreich ataxia (FRDA) [[1]] LeeVJ (talk) 22:36, 11 March 2009 (UTC)

General Problems

I'm trying not to be overly critical, but I came across this article and am somewhat frustrated. I realize that this is a very large topic, and no article can completely cover everything. I did my Ph.D. dissertation on repeat expansion diseases, so I realize that I might be a lot more picky about some of these things. For this reason I have decided not to attempt to edit this page because: a) I wouldn't know where to start, b) people would probably become frustrated by the amount of detail I would include and consider the article to be "way too much information" (understandably), and c) unfortunately I don't have as much free time as I wish I did to contribute to some of the pages here. In general I think that current and future versions of this article should keep in mind the following considerations (many of which apply in general to any article dealing with any expanding field of knowledge):

Since this is such a large topic, it is unrealistic to expect all of the information to reflect up-to-the-minute developments. Therefore, it is important to stress that the precise mechanisms of how repeat expansions occur are not well understood. Also, for some of the diseases, the mechanisms of how the repeat expansion mutations cause the symptoms of the diseases are not well understood. There are several hypotheses and opposing schools of thought as to how and when the expansion mutations occur in the first place (replication vs. recombination, DNA slippage vs. evasion of DNA repair, or various combinations of these processes and others). You may come across a scientific journal article where the author gives the impression of having the definitive and final answer on these mechanisms. However, it is not uncommon to meet scientists who think they have all the answers to everything -- I happen to work with several of them. But the truth is that we still have much more to learn in this field, so any mention of a particular mechanism should be clarified as being one of the several hypothesis that are still under debate.

While much of the information is outdated and/or incomplete, this is of course to be expected in scientific articles where the field is always expanding. Contributors should be careful to point this out whenever appropriate so that newcomers to the topic will not be led to believe that the statements made are the final word on the topic. I have added links to PubMed and a few other "real-time" resources that would be helpful for those who want more information:

PubMed (http://www.ncbi.nlm.nih.gov/pubmed/). Although many of these articles are highly specialized and probably beyond the scope of what many readers are interested in, there is an option to search for "Review" articles only, and these tend to be a bit more reader-friendly.

National Institute of Neurological Disorders and Stroke (http://www.ninds.nih.gov/disorders/disorder_index.htm). This is a useful resource since many of the repeat expansion diseases are neurological or neuromuscular disorders.

Genetics Home Reference (http://ghr.nlm.nih.gov/). This is maintained by the NIH and National Library of Medicine. Much of the information is written for non-experts, but even as a geneticist I often refer to these pages as a starting point for information on diseases that are outside my area of expertise.

Once again, I don't want to be too critical, but I also think it is important for contributors to keep in mind that many topics in science (and other fields) are constantly changing. It is important to indicate whether or not a topic is still not well understood or is still under debate. Beth L Rogers (talk) 21:36, 24 June 2009 (UTC)

Thankyou for your comments (constructive critism is always useful ), your concerns tally with the medicine projects guidelines ( see WP:MEDMOS and WP:RS ), which one day will have been applied to all articles (hopefully), in the meantime if you have any further specific amendments please add and this will aid any editors that arrive, L∴V 11:46, 30 June 2009 (UTC)

Proposal: include longer repeats

I was about to add PROMM, HDL1 and HDL2 to the list but then noticed the discussion above. As far as I can tell there is no Wikipedia page that covers oligonucleotide repeat disorders (if that's the right term) other than this one. I would therefore suggest adding this information (I'd be happy to do so myself) and broadening the scope of the page. We could keep the page title as it is, have a separate section for 'other repeat lengths' and redirect appropriate terms to it.

Thoughts?

Neurotip (talk) 12:12, 20 September 2011 (UTC)

@Neurotip: I am thinking about doing something similar as well. A lot of the non-PolyQ problems happen with non-coding parts of the mRNA (or even ncRNAs), and are not really limited to keeping things in frame. We should probably rename the page to something like "microsatellite expansion disorder" or "microsatellite expansion diseases". PMID 28851463 seems to provide a neat list of these things. --Artoria2e5 🌉 04:23, 4 May 2019 (UTC)

I think Wikipedia needs information on other expansion disorders apart from those with 3 base pair repeat units.

One option is to create another page "Repeat Expansion Disorder" (the common term) describing these in general. This approach would result in a lot of duplicated information.

My suggestion is to move this page to "Repeat Expansion Disorder" and include a section on trinucleotide expansion disorders. The first sentence mentions there are over 50 known disorders, but this is the number for repeat expansion disorders in general, and the number for trinucleotide expansions is closer to 35. This article might be useful to update this page PMC8205997. Tank (talk) 06:22, 21 November 2023 (UTC)

Very casually/conversationally written.

I'm not sure how to import the little info box for it (if there is one), but this article doesn't comply with WP:TONE. horsedreamer 16:47, 9 March 2015 (UTC)

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Working on repeat expansion disorder page

I am planning to work on a repeat expansion disorder page (which is a superset of trinucleotide repeat expansion disorders). This may be repeating a lot of the information on this page. We can then decide how these two articles will complement each other. TrickyTank (talk) 02:24, 28 November 2023 (UTC)