MELAS: a mitochondrial disorder in an adult patient with a renal transplant.

Mitochondrial diseases are a heterogeneous group of syndromes caused by genetic defects in mitochondrial DNA (mtDNA) or nuclear-encoded mitochondrial genes. They present with a wide range of clinical phenotypes. Myopathy may be the sole or main sign, or merely an incidental finding occurring in the late course of a multisystemic illness. Although mitochondrial disorders are increasingly being recognized, confirming a specific diagnosis remains a great challenge due to the clinical heterogeneity of the diseases. Several well-defined clinical syndromes associated with specific mutations have been described. Thus, suspicion of mitochondrial diseases among patients with multiple, seemingly unrelated neuromuscular and multisystem disorders should be confirmed by the finding of deleterious mutations in genes involving mitochondrial biogenesis and function. This case report describes a 58-year-old patient with a 40-year course of a multisystemic illness representing the diagnostic challenges of mitochondrial disease.