C08 Knockout of mismatch repair genes MLH1 and MSH3 ablates expansion of the CAG repeat in a human iPSC model of Huntington's disease. (12th September 2022)

• Record Type: Journal Article
• Authors: Stone, Joseph; Massey, Thomas; Allen, Nicholas; Jones, Lesley
• Is Part Of: Journal of neurology, neurosurgery and psychiatry. Volume 93(2022)Supplement 1
• Page Start: A18
• Page End: A19
• Publication Date: 2022-09-12
• Subjects: Modifiers -- expansion -- MMR -- iPSCs -- CRISPR; Neurology -- Periodicals; Nervous system -- Surgery -- Periodicals; Psychiatry -- Periodicals; 616.8
• DOI: 10.1136/jnnp-2022-ehdn.52
• Languages: English
• ISSNs: 0022-3050

Abstract

Abstract : Background: Huntington's disease (HD) is caused by expansion of a CAG repeat in exon 1 of the Huntingtin gene (HTT). Whilst age of disease onset inversely correlates with CAG repeat length, inheritance of other genetic factors act as disease modifiers and account for considerable variability in age of disease onset across the HD patient population. Genome wide association studies have now identified DNA damage repair genes as modifiers of disease onset. DNA mismatch repair (MMR) genes including MLH1, PMS1, PMS2 and MSH3 are implicated. Evidence from mouse models of HD implicate MLH1, MLH3 and MSH3 in driving CAG repeat expansion in somatic cells, hypothesised to accelerate pathogenesis and decrease the age of disease onset. Methods: To investigate the role of the mismatch repair genes in HD we have established an in vitro model of CAG repeat expansion in a patient derived induced pluripotent stem cell (iPSC) line with 109 CAG repeats. We have used CRISPR Cas9 gene editing technology to knockout (KO) MLH1, MSH3, MLH3 and PMS1 in this cell line and determined changes in CAG repeat length over time in cultured MLH1 and MSH3 KO iPSCs. Results and Conclusions: CAG repeat expansion observed in the parent cell line is ablated by knocking out either MLH1 or MSH3 in cultured iPSCs (n=6, P<0.05). Heterozygous KO of MLH1 does not reduce expansion relative to unedited controls (n=6, P<0.05). Our findings and cell models provide a platform for understanding mechanisms of CAG repeat expansion and insight into potential therapeutics.