Exercise capacity and idebenone intervention in children and adolescents with Friedreich ataxia

Abstract

Objective: To determine the exercise capacity of children and adolescents with Friedreich's Ataxia (FA) and to evaluate the effects of 6 months of idebenone treatment on exercise capacity.

Design: Exploratory endpoint in a randomized double-blind, placebo-controlled, phase II clinical trial designed to investigate the effects of idebenone on a biomarker of oxidative stress.

Setting: Exercise physiology laboratory in a single clinical research center.

Participants: Ambulatory subjects (N=48; age range, 9-17 y) with genetically confirmed FA.

Intervention: Idebenone administered orally 3 times a day for a total daily dose of approximately 5, 15, and 45 mg/kg or matching placebo for 6 months.

Main outcome measures: Peak oxygen consumption per unit time (peak VO(2)) and peak work rate (WR) were measured during incremental exercise testing at baseline and after treatment. Echocardiography and neurologic assessments were also completed before and after treatment.

Results: Baseline mean peak VO(2) +/- SD was 746+/-246 mL/min (16.2+/-5.8 mL/kg/min), and WR was 40+/-23 W for all subjects. Peak VO(2) and WR were correlated with short guanine-adenine-adenine allele length and neurologic function. Relative left ventricular wall thickness was increased but left ventricular ejection fraction was normal in most subjects; there was no relationship between any exercise and echocardiographic measures. There were no significant changes in mean peak VO(2) or WR after idebenone treatment at any dose level relative to placebo.

Conclusions: Exercise capacity in children and adolescents with FA was significantly impaired. The basis for the impairment appears to be multifactorial and correlated to the degree of neurologic impairment. Although idebenone has previously been shown potentially to improve features of FA, idebenone treatment did not increase exercise capacity relative to placebo.

Trial registration: ClinicalTrials.gov NCT00229632.

Fig 1

CONSORT Diagram

Fig 2

Relationship between Peak Oxygen Consumption (peak VO₂) and Peak Work Rate. A generally linear relationship was observed indicating that higher Peak work rates were associated with greater peak VO₂.

Figure 3

Relationships between PeakVO₂ and the short guanine adenine adenine repeat length (GAA1, panel A), Friedreich’s Ataxia Rating Scale (FARS, panel B) and International Cooperative Ataxia Rating Scale (ICARS, panel C). Higher PeakVO₂ was generally associated with lower GAA1 repeat length, FARS and ICARS scores. Lower FARS and ICARS scores indicate less disability.

Figure 4

Relationships between PeakVO₂ and the short guanine adenine adenine repeat length (GAA1, panel A), Friedreich’s Ataxia Rating Scale (FARS, panel B) and International Cooperative Ataxia Rating Scale (ICARS, panel C). Higher peak work rate was generally associated with lower GAA1 repeat length, FARS and ICARS scores. Lower FARS and ICARS scores indicate less disability.