Time to harmonize mitochondrial syndrome nomenclature and classification: A consensus from the North American Mitochondrial Disease Consortium (NAMDC)

Objective: To harmonize terminology in mitochondrial medicine, we propose revised clinical criteria for primary mitochondrial syndromes. Methods: The North American Mitochondrial Disease Consortium (NAMDC) established a Diagnostic Criteria Committee comprised of members with diverse expertise. It included clinicians, researchers, diagnostic laboratory directors, statisticians, and data managers. The Committee conducted a comprehensive literature review, an evaluation of current clinical practices and diagnostic modalities, surveys, and teleconferences to reach consensus on syndrome definitions for mitochondrial diseases. The criteria were refined after manual application to patients enrolled in the NAMDC Registry. Results: By building upon published diagnostic criteria and integrating recent advances, NAMDC has generated updated consensus criteria for the clinical definition of classical mitochondrial syndromes. Conclusions: Mitochondrial diseases are clinically, biochemically, and genetically heterogeneous and therefore challenging to classify and diagnose. To harmonize terminology, we propose revised criteria for the clinical definition of mitochondrial disorders. These criteria are expected to standardize the diagnosis and categorization of mitochondrial diseases, which will facilitate future natural history studies and clinical trials.