Evidence of cardiovascular autonomic impairment in mitochondrial disorders

Objective: To investigate autonomic nervous system (ANS) function in mitochondrial disorders (MD). Background: MD are characterized by a wide range of clinical features, including heart abnormalities and peripheral and central nervous systems involvement. Rarely autonomic symptoms have been reported. Methods: 22 patients with MD underwent a battery of cardiovascular reflex tests including five tests of parasympathetic function and four tests of sympathetic function. Power spectral analyses (PSA) of heart rate variability in the supine and upright positions were also evaluated. Plasma levels of adrenaline, noradrenaline and dopamine were determined in the standing and lying positions. Results: Only 4/22 patients referred symptoms related to ANS dysfunction. 46% of patients had a definite autonomic damage (i. e. an autonomic score ≥ 4). 36% showed moderate alterations with an autonomic score in the range 2-3 and 18 % had a normal autonomic function. MD patients had a significantly (p <0.03) lower increase of adrenaline level after standing. Conclusions: Our data indicate an autonomic dysfunction in more than 80% of MD patients, even in the absence of a clinically manifested autonomic involvement. Cardiovascular autonomic investigation might be systematically employed in the characterization of MD.