Quality improvement of mitochondrial respiratory chain complex enzyme assays using Caenorhabditis elegans

The diagnosis of a mitochondrial disorder relies heavily on the enzymatic analysis of mitochondrial respiratory chain complexes in muscle or other tissues. However, considerable differences exist between clinical laboratories in the protocols or particular tests used for evaluation. In addition, laboratories can encounter difficulties in consistent technique, as well as procurement of adequate positive or negative controls. Currently, there is no external quality assurance for respiratory chain complex assays. In this study, we explored the use of Caenorhabditis elegans mitochondria as a potential aid to diagnostic centers that perform respiratory chain complex assays.

Five diagnostic test centers in the United States and one from Australia comparatively analyzed enzyme activities of mitochondria from C. elegans. The first survey consisted of three open-labeled samples including one normal control and two mutants; the second survey consisted of one open-labeled normal control and two blinded samples.

There was very good concordance among laboratories in detecting the majority of the defects present in the mutant specimens. Despite the ability to detect respiratory chain complex defects, the scatter between centers for certain enzymatic assays, particularly I + III, II, III, and IV, led to different diagnostic interpretations between the centers.

The data strongly support the need for comparative testing of mitochondrial enzyme assays between multiple laboratories. Our overall results are encouraging for the use of nematode mitochondria as a tool that might provide a virtually inexhaustible supply of mitochondria with defined defects for development of assays and as a potential source of control specimens.