Mitochondrial diseases occur when insufficient energy is produced, affect both adults and children and often require a muscle biopsy to help the investigation and diagnosis. We have identified the same genetic defect – a mutation within the NDUFB3 gene – in ten children from eight families with identical physical features; affected children are short, have prominent foreheads and were noted to be developing slowly during pregnancy. These children have recovered well whereas many other mitochondrial genetic defects have a fatal outcome. Early recognition of this combination of physical features could lead to other children being diagnosed without requiring an invasive muscle biopsy. (By Dr. Charlotte Alston, http://jmg.bmj.com/content/early/2016/04/18/jmedgenet-2015-103576 )