Goldenthal et al. (Mol Gen and Metab 105 (2012) 457-462) recently published a method for evaluating respiratory chain (RC) complex I and IV activity and citrate synthase via a buccal swab sample. They report more than an 82% correlation between buccal sample and muscle tissue deficiencies.  The availability of this test adds to the arsenal of tools in the often times difficult to make diagnosis of mitochondrial disease. I have actually already had a patient referred to me with results from this test, so it is already making its way into the clinical setting.
Hilary Vernon, MD PhD