Global DNA methylation is not elevated in blood samples from Machado-Joseph disease mutation carriers

Abstract

Machado-Joseph disease (MJD) is an autosomal dominant spinocerebellar ataxia (SCA) caused by a polyglutamine expansion in the ataxin-3 protein, which initiates a cascade of pathogenic events, including transcriptional dysregulation. Genotype-phenotype correlations in MJD are incomplete, suggesting an influence of additional factors, such as epigenetic modifications, underlying the MJD pathogenesis. DNA methylation is known to impact the pathophysiology of neurodegenerative disorders through gene expression regulation and increased methylation has been reported for other SCAs. In this work we aimed to analyse global methylation in MJD carriers. Global 5-mC levels were quantified in blood samples of 33 MJD mutation carriers (patients and preclinical subjects) and 33 healthy controls, matched by age, sex, and smoking status. For a subset of 16 MJD subjects, a pilot follow-up analysis with two time points was also conducted. No differences were found in median global 5-mC levels between MJD mutation carriers and controls and no correlations between methylation levels and clinical or genetic variables were detected. Also, no alterations in global 5-mC levels were observed over time. Our findings do not support an increase in global blood methylation levels associated with MJD.

Keywords: DNA methylation; Machado-Joseph disease; SCA3; epigenetic modifiers; polyq disorders.

Figure 1.

Global 5-mC levels in MJD mutation carriers. (a) Box plots for the global 5-mC levels in 33 MJD mutation carriers (MJD) and age-, sex- and smoking status-matched healthy controls (CTRL). (b) Box plots for the global levels of 5-mC in 14 preclinical subjects (MJD-PC) and age-, sex- and smoking status-matched healthy controls (CTRL-PC). (c) Box plots for the global 5-mC in 19 MJD patients (MJD-P) and age-, sex- and smoking status-matched healthy controls (CTRL-P). (d) Box plots for the global levels of 5-mC in 14 preclinical subjects (MJD-PC) and 19 MJD patients (MJD-P).

Figure 2.

Follow-up analysis of global 5-mC levels in MJD mutation carriers. 5-mC levels in the two collection timepoints (baseline and visit 1) for each MJD subject (n=16), including patients 6 preclinical carriers and 10 patients. The delta value is the difference of the global 5-mC % between visit 1 and the baseline for each MJD subject. MJD subjects with a decrease in global 5-mC levels are highlighted in bold.