Fatigue in primary genetic mitochondrial disease: No rest for the weary.

Rates of perceived fatigue, anxiety, depression, sleepiness and mitochondrial disease severity were assessed prospectively in 2017-2018 using established validated questionnaires in 48 adult patients with genetically confirmed primary mitochondrial disease. Fatigue was found to be very common among patients with primary mitochondrial disease, with 34 to 48 (71-100%) patients reporting fatigue depending on the measure used, and the severity of fatigue correlating with the severity of disease. Moderate-to-severe depression (10/48; 20.8%) anxiety (28/48; 58.3%) and sleep problems (16/48; 33.3%) were frequent in our patients with fatigue and these conditions were even more prevalent in those with severe fatigue. In conclusion, perceived fatigue was common in patients with primary mitochondrial disease and appeared to correlate with disease severity. Depression, anxiety and sleep disorders were more common in the cohort than those with other chronic diseases but with rates similar to that seen in multiple sclerosis. The severity of perceived fatigue correlated with an increased risk of these comorbid conditions. The Fatigue Severity Scale may more selectively measure non-anxiety/sleep-related fatigue in primary mitochondrial disease and additional testing is planned.