Abstract
Barth syndrome (BTHS) is an ultra-rare, X-linked recessive disorder characterized by cardio-skeletal myopathy, exercise intolerance, and growth delay. Oxygen uptake during peak exercise (VO2peak) has been shown to be severely limited in individuals with BTHS however; the trajectory of VO2peak from childhood to young adulthood is unknown. The objective of this study was to describe VO2peak from childhood through young adulthood in BTHS. Methods and Materials: VO2peak over time was presented through cross-sectional (n = 33 participants) and a longitudinal analyses (n = 12 participants). Retrospective data were obtained through maximal exercise testing on a cycle ergometer from individuals with BTHS who were or are currently enrolled in a research study during July 2006-September 2017. Participants included in the cross-sectional analysis were divided into 3 groups for analysis: 1) children (n = 13), 2) adolescents (n = 8), and 3) young adults (n = 12). Participants in the longitudinal analysis had at least two exercise tests over a span of 2–9 years. Results: VO2peak relative to body weight (ml/kgBW/min), fat-free mass (FFM) and by percent of predicted VO2peak obtained were not significantly different between children, adolescents and young adults. VO2peak did not longitudinally change over a mean time of ~5 years in late adolescent and young adult participants with repeated tests. A model including both cardiac and skeletal muscle variables best predicted VO2peak. Conclusions: In conclusion, VO2peak relative to body weight and fat-free mass demonstrates short- and long-term stability from childhood to young adulthood in BTHS with some variability among individuals.
Highlights
Barth syndrome (BTHS) is an ultra-rare (1/300,000 births [1]), X-linked recessive disorder characterized by cardio-skeletal myopathy, exercise intolerance, neutropenia, growth delay and 3-methylglutaconic acid [2, 3]
Maximum oxygen uptake (VO2max), a concept first proposed by Hill et al in 1923 [8, 9], is defined as the highest rate of oxygen uptake and utilization by the body during intense, maximal exercise that no further increases in work rate bring on additional rises in VO2 [10]
Body mass index (BMI) and fat-free mass were greater in young adults vs. children were not different between children vs. adolescents or adolescents vs. young adults
Summary
Barth syndrome (BTHS) is an ultra-rare (1/300,000 births [1]), X-linked recessive disorder characterized by cardio-skeletal myopathy, exercise intolerance, neutropenia, growth delay and 3-methylglutaconic acid [2, 3]. In BTHS, mutations in the tafazzin gene (TAZ, located on Xq28), cause abnormal phospholipid metabolism mainly by affecting mitochondrial cardiolipin [4]. Maximum oxygen uptake (VO2max), a concept first proposed by Hill et al in 1923 [8, 9], is defined as the highest rate of oxygen uptake and utilization by the body during intense, maximal exercise that no further increases in work rate bring on additional rises in VO2 (i.e. plateau) [10]. VO2peak is a measure that combines cardiovascular and skeletal muscle oxidative function (i.e. Fick equation: oxygen uptake = cardiac output x arteriovenous oxygen difference [12]), as well as pulmonary ventilation and diffusion capacity, and reflects the integrated ability to transport oxygen from atmospheric air to the mitochondria to perform work [13]. After adjusting for age and other risk factors, VO2peak is one of the best predictors of cardiovascular [16, 17] and overall mortality [18, 19] in adults and is routinely used in the diagnosis of mitochondrial disease [20, 21]
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