Abstract
A 34-year-old man presents with recurrent episodes of acute reversible muscle weakness, soreness, pain, cramps and myoglobinuria with elevated creatine kinase. Symptoms were triggered by fasting, sustained long duration exercise and viral infection. A metabolic myopathy was suspected. Genetic testing showed a homozygous pathogenic variant in CPT2 gene resulting in deficiency of Carnitine Pamitoyl transferase II, an enzyme in the carnitine cycle. The cycle plays a vital role in transport of long chain hydrophobic fatty acids from the cytosol into the mitochondrial matrix for the production of energy via β-oxidation. Carnitine Pamitoyl transferase II deficiency is the most common inherited disorder of lipid metabolism affecting the skeletal muscle of adults. It is also the most frequent cause of hereditary myoglobinuria across all ages. Our case presents an analysis of important clinical features of carbohydrate and lipid metabolism disorders. It highlights how thermolability of the mutant enzyme, rather than its actual deficiency, explains triggering of muscle symptoms by prolonged exercise, infections, febrile episodes, or exposure to cold.
