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A genetic association study of glutamine-encoding DNA sequence structures, somatic CAG expansion, and DNA repair gene variants, with Huntington disease clinical outcomes

Ciosi, M; Maxwell, A; Cumming, SA; Hensman Moss, DJ; Alshammari, AM; Flower, MD; Durr, A; ... Monckton, DG; + view all (2019) A genetic association study of glutamine-encoding DNA sequence structures, somatic CAG expansion, and DNA repair gene variants, with Huntington disease clinical outcomes. EBioMedicine 10.1016/j.ebiom.2019.09.020. (In press). Green open access

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Abstract

BACKGROUND: Huntington disease (HD) is caused by an unstable CAG/CAA repeat expansion encoding a toxic polyglutamine tract. Here, we tested the hypotheses that HD outcomes are impacted by somatic expansion of, and polymorphisms within, the HTT CAG/CAA glutamine-encoding repeat, and DNA repair genes. METHODS: The sequence of the glutamine-encoding repeat and the proportion of somatic CAG expansions in blood DNA from participants inheriting 40 to 50 CAG repeats within the TRACK-HD and Enroll-HD cohorts were determined using high-throughput ultra-deep-sequencing. Candidate gene polymorphisms were genotyped using kompetitive allele-specific PCR (KASP). Genotypic associations were assessed using time-to-event and regression analyses. FINDINGS: Using data from 203 TRACK-HD and 531 Enroll-HD participants, we show that individuals with higher blood DNA somatic CAG repeat expansion scores have worse HD outcomes: a one-unit increase in somatic expansion score was associated with a Cox hazard ratio for motor onset of 3·05 (95% CI = 1·94 to 4·80, p = 1·3 × 10-6). We also show that individual-specific somatic expansion scores are associated with variants in FAN1 (pFDR = 4·8 × 10-6), MLH3 (pFDR = 8·0 × 10-4), MLH1 (pFDR = 0·004) and MSH3 (pFDR = 0·009). We also show that HD outcomes are best predicted by the number of pure CAGs rather than total encoded-glutamines. INTERPRETATION: These data establish pure CAG length, rather than encoded-glutamine, as the key inherited determinant of downstream pathophysiology. These findings have implications for HD diagnostics, and support somatic expansion as a mechanistic link for genetic modifiers of clinical outcomes, a driver of disease, and potential therapeutic target in HD and related repeat expansion disorders. FUNDING: CHDI Foundation.

Type: Article
Title: A genetic association study of glutamine-encoding DNA sequence structures, somatic CAG expansion, and DNA repair gene variants, with Huntington disease clinical outcomes
Location: Netherlands
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.ebiom.2019.09.020
Publisher version: https://doi.org/10.1016/j.ebiom.2019.09.020
Language: English
Additional information: © 2019 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license. (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Keywords: Genetic association study, Somatic expansion, DNA repair, Huntington disease
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > UCL Queen Square Institute of Neurology
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > UCL Queen Square Institute of Neurology > Neurodegenerative Diseases
URI: https://discovery.ucl.ac.uk/id/eprint/10083891
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