Defects in complex IV of the respiratory chain may result in a variety of phenotypes and be caused by mutations in 20 genes, most of which are involved in assembly of the complex. Here, we have for the first time identified mutations in COA3 as a cause of complex IV deficiency in a patient with neuropathy, exercise intolerance, obesity and short stature. The mutations were identified by whole exome sequencing. COA3 encodes a protein that is involved in the early assembly of complex IV, and likely functions in a complex that stabilizes a COX1 assembly intermediate. (By Dr. Elsebet Ostergaard, http://jmg.bmj.com/content/early/2015/01/20/jmedgenet-2014-102914)