Several previous blog entries discussed trinucleotide repeats. From two scientists about as physically far apart as one can get on our planet comes information about two genes that have what are called hexanucleotide repeats.
- The NOP56 gene is in the p13 region of chromosome 20. In much DNA there are untranslated regions (abbreviated at UTRs), introns and exons. When the translation of the DNA is being done UTRs and exons are kept but introns are dropped. There can be multiple introns and exons. In an area called intron1 the sequence GGCCTG is typically repeated 3 to 14 times. It is not clear (yet) what exactly the repeats do, but Spinocerebellar ataxia type 36 (SCA36) has been linked to people with 650 (!) or more repeats. One preliminary finding is that distortions in NOP56 may disrupt the functioning of a nearby gene called MIR1292 which provides instructions for making a type of RNA that regulates the activity of genes that produce proteins called glutamate receptors. Of interest here is that we may be seeing an example of what some have charmingly called MORON = ‘mutate one ruin one nearby ‘ in the manner of BOGO (=buy one get one) seen in marketing.
- The c9orf72 gene is in the p21.2 region of chromosome 9. Here the hexanucleotide repeat is GGGGCC. This can occur up to 30 times with no immediate negative effect on gene function. It is strongly believed that more than 30 repeats causes amyotrophic lateral sclerosis (ALS). It is also possible to show symptoms of frontotemporal dementia (FTD). More work is going on.