Blood DDIT4 and TRIM13 transcript levels mark the early stages of Machado-Joseph disease

Machado-Joseph disease (MJD) is a rare late-onset polyglutamine neurodegenerative disease caused by the expansion of a CAG repeat in the ATXN3 gene encoding the ataxin- 3 (ATXN3) protein. Several studies have identified changes in the abundance of select transcripts and proteins in blood samples of MJD mutation carriers. Here, we aimed to: 1) identify blood transcriptional changes that could be potential biomarkers of MJD from preclinical to symptomatic disease stages; 2) correlate levels of differentially expressed transcripts in blood of MJD carriers with demographic, genetics, and clinical features; and 3) evaluate whether the identified differential abundance of selected transcripts in blood of MJD subjects is preserved in post-mortem brains of MJD patients. Using real- time quantitative PCR, we observed consistent dysregulation of DDIT4, TRIM13 and P2RY13 transcript levels in blood samples of MJD subjects from different disease stages (from preclinical to symptomatic), and of patients from two cohorts with different backgrounds (Azores and Brazil). Importantly, combined blood DDIT4 and TRIM13 transcript levels display a very high accuracy to discriminate MJD carriers in preclinical stage, early-stage patients, and patients with more than five years of disease duration from respective controls (AUC=1.00, AUC=0.96, and AUC=0.90, respectively). Moreover, in the combined group of Azorean and Brazilian patients, blood levels of P2RY13 transcript correlate with age at onset, and abundance of DDIT4 and TRIM13 transcripts correlate with the CAG repeat size of the expanded ATXN3 allele. In the subgroup of early-stage Azorean patients, blood levels of TRIM13 transcripts correlate with age at disease onset. Interestingly, abundance of DDIT4, TRIM13 and P2RY13 proteins is also altered in brains of MJD patients. In summary, this work shows that blood DDIT4 and TRIM13 transcript levels are potentially blood-based biomarkers of MJD of special usefulness in marking preclinical and early stages of the disease, and points for common dysregulated processes involving DDIT4, TRIM13 and P2RY13 in the blood and the brain of MJD subjects.