Back in February of this year (2010) a study in Nature reported on finding a segment of human DNA, one of the areas in the so-called ‘junk genes,’ that contributed to a form of coronary artery disease. [SciTechStory: Junk DNA that actually does something] Now there is another study, in the magazine Science [A Unifying Genetic Model for Facioscapulohumeral Muscular Dystrophy] by a large international team of researchers (France, Netherlands, Spain, USA), that discovered another instance where a ‘junk gene’ plays a major role in a disease, in this case muscular dystrophy.
First and foremost, this is an important finding for the study and treatment of specifically facioscapulohumeral muscular dystrophy or FSHD, one of the most common forms, as it reveals a particular gene, repeated at the end of chromosome 4 (4q35), is the key to triggering onset of FSHD.
It is also, as an article in the New York Times puts it (August 19, 2010: Reanimated ‘Junk’ DNA is Found to Cause Disease), the surprising activation of a ‘dead’ gene. Dead in the sense that the areas of junk DNA are non-coding, meaning they’re not used to create protein.
Actually, not so surprising. The areas of ‘junk DNA’ comprise about 98% of the human genome, which in itself is a curiously high percentage. It shouldn’t be surprising that with all that material, from time to time it is discovered that – lo and behold – one of the junk genes does something.
In this case, the role of the gene is quite specific and the configuration is complicated. This gene, located at the end of chromosome 4, is often repeated – a trailer of ‘dead genes.’ Chromosome 4 has for decades been observed as a trouble spot, but these ‘dead genes’ were ignored. In the recent study however, it was discovered that people who have 10 or less copies of the gene were much more likely to develop FSHD. (In fact, people with more than 10 copies never get the disease.) It was also learned that this gene doesn’t create protein (normally) but it is always transcribed (copied by RNA), the first step in using a gene – only it falls apart shortly after transcription. If, however, a middle section of the chromosome 4 DNA, called poly (A), is present the transcribed genes are stabilized and they go on to be expressed (creating proteins) that contribute to the development of FSHD.
This is an unusually specific set of circumstances, but it does illustrate that while the mass of ‘junk DNA’ may be inert (biologically) most of the time, it is premature with our current state of knowledge to assume that all of these genes remain inactive at all times. It’s becoming apparent that in all likelihood there are more ‘dead genes’ linked to various diseases, just as there are studies showing that some of the ‘junk DNA’ is involved in gene regulation.
Does this all add up to finding that ‘junk DNA’ isn’t junk? Not necessarily. At this point, most biologists still feel that we carry an enormous amount of vestigial and inactive DNA. Of course, with discoveries like the ones involving muscular dystrophy or coronary artery disease, if even a few percent of the ‘junk DNA’ turns out to be either active or potentially active under certain conditions; these areas of our genome may still become an important chapter in the book on DNA coding.
The bigger lesson, Dr. Collins [Director of the United States National Institute of Health] said, is that diseases can arise in very complicated ways. Scientists used to think the genetic basis for medical disorders, like dominantly inherited diseases, would be straightforward. Only complex diseases, like diabetes, would have complex genetic origins.
“Well, my gosh,” Dr. Collins said. “Here’s a simple disease with an incredibly elaborate mechanism.”
[Source: New York Times]