Primary mitochondrial diseases remain difficult to diagnose. Many patients with a phenotype concerning for mitochondrial disease are unable to receive genetic confirmation.  In these instances, diagnostic terms such as “unlikely,” “possible” or “probable” mitochondrial disease are often used.

Advances in genomic testing have shown that some patients with a clinical phenotype and biochemical abnormalities suggesting mitochondrial disease may have other genetic disorders – and there are a growing number of phenocopies of mitochondrial disease.

In this article we review some of the strengths and weaknesses of current testing modalities, the number of phenocopies identified and how a diagnosis of “possible” mitochondrial disease may result in harm to patients and their families – potentially creating anxiety, delaying appropriate diagnosis and leading to inappropriate management or care.

We make the recommendation that for patients without a genetically confirmed diagnosis – a categorization of “diagnosis uncertain” is preferred over terms such as “possible” or “probable” mitochondrial disease. (By Dr. Sumit Parikh, https://jmg.bmj.com/content/early/2019/01/25/jmedgenet-2018-105800 )