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Open chromatin structure in PolyQ disease-related genes: a potential mechanism for CAG repeat expansion in the normal human population.

ABSTRACT: The human genome contains dozens of genes that encode for proteins containing long poly-glutamine repeats (polyQ, usually encoded by CAG codons) of 10Qs or more. However, only nine of these genes have been reported to expand beyond the healthy variation and cause diseases. To address whether these nine disease-associated genes are unique in any way, we compared genetic and epigenetic features relative to other types of genes, especially repeat containing genes that do not cause diseases. Our analyses show that in pluripotent cells, the nine polyQ disease-related genes are characterized by an open chromatin profile, enriched for active chromatin marks and depleted for suppressive chromatin marks. By contrast, genes that encode for polyQ-containing proteins that are not associated with diseases, and other repeat containing genes, possess a suppressive chromatin environment. We propose that the active epigenetic landscape support decreased genomic stability and higher susceptibility for expansion mutations.

SUBMITTER: Sorek M

PROVIDER: S-EPMC7671342 | biostudies-literature | 2019 Apr

REPOSITORIES: biostudies-literature

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Open chromatin structure in PolyQ disease-related genes: a potential mechanism for CAG repeat expansion in the normal human population.

Sorek Matan M Cohen Lea R Z LRZ Meshorer Eran E

NAR genomics and bioinformatics 20190401 1

The human genome contains dozens of genes that encode for proteins containing long poly-glutamine repeats (polyQ, usually encoded by CAG codons) of 10Qs or more. However, only nine of these genes have been reported to expand beyond the healthy variation and cause diseases. To address whether these nine disease-associated genes are unique in any way, we compared genetic and epigenetic features relative to other types of genes, especially repeat containing genes that do not cause diseases. Our ana ...[more]

PMID: 33575550

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Project description:Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant neurodegenerative disorder caused by an expansion of a polyglutamine tract within the ATXN1 gene. Normal alleles have been reported to range from 6 to 35 repeats, intermediate alleles from 36 to 38 repeats and fully penetrant pathogenic alleles have at least 39 repeats. This distribution was based on relatively few samples and the narrow intermediate range makes the accuracy of the repeat sizing crucial for interpreting and reporting diagnostic tests, which can vary between laboratories. Here, we examine the distribution of 6378 SCA1 chromosomes and identify a very late onset SCA1 family with a fully penetrant uninterrupted pathogenic allele containing 38 repeats. This finding supports the theory that polyQ toxicity is related to the increase of the length of the inherited tracts and not as previously hypothesized to the structural transition occurring above a specific threshold. In addition, the threshold of toxicity shifts to a shorter polyQ length with the increase of the lifespan in SCA1. Furthermore, we show that SCA1 intermediate alleles have a different behavior compared to the other polyglutamine disorders as they do not show reduced penetrance when uninterrupted. Therefore, the pathogenic mechanism in SCA1 is distinct from other cytosine-adenine-guanine (CAG) repeat disorders. Accurately sizing repeats is paramount in precision medicine and can be challenging particularly with borderline alleles. We examined plasmids containing cloned CAG repeat tracts alongside a triplet repeat primed polymerase chain reaction (TP PCR) CAG repeat ladder to improve accuracy in repeat sizing by fragment analysis. This method accurately sizes the repeats irrespective of repeat composition or length. We also improved the model for calculating repeat length from fragment analysis sizing by fragment analyzing 100 cloned repeats of known size. Therefore, we recommend these methods for accurately sizing repeat lengths and restriction enzyme digestion to identify interruptions for interpretation of a given allele's pathogenicity.

Dataset Information

Open chromatin structure in PolyQ disease-related genes: a potential mechanism for CAG repeat expansion in the normal human population.

Publications

Open chromatin structure in PolyQ disease-related genes: a potential mechanism for CAG repeat expansion in the normal human population.

Similar Datasets

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