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Mitochondrial enzyme deficiency causing exercise limitation in normal-appearing adults
R G Hooper1, A R Thomas, R A Kearl
1St. Luke's Charles A Barrow Heart Lung Center, Phoenix, AZ.
Chest
|February 1, 1995
Summary
Mitochondrial enzyme deficiencies, typically seen in children, can cause exercise limitation in adults. These deficiencies affect cellular energy metabolism, leading to unexplained symptoms like fatigue and shortness of breath.
Area of Science:
- Biochemistry
- Exercise Physiology
- Neurology
Background:
- Mitochondrial enzyme deficiencies are known causes of pediatric neurologic disorders.
- Isolated myopathy due to these deficiencies is rarely reported in adults.
Observation:
- Three adults presented with unexplained exertional dyspnea, tachycardia, and fatigue.
- Exercise testing revealed abnormal cellular energy metabolism, with normal oxygen transport and gas exchange.
- Significant increases in cardiac output, heart rate, and lactic acid were observed during exercise.
Findings:
- Muscle morphology was normal, but mitochondrial enzyme assays confirmed deficiencies in all patients.
- Exercise testing indicated altered cellular energy metabolism as the cause of symptoms.
Implications:
- Mitochondrial enzymatic deficiencies can manifest as unexplained exercise limitation in adults.
- Clinicians should consider cellular energy metabolism abnormalities in patients with exertional symptoms.
- The incidence of adult-onset mitochondrial myopathy may be underestimated.