“Multiple mitochondrial DNA Deletions” refers to the different sized pieces of mitochondrial DNA that are missing. The genetic problem here is often inherited, but is not due to a mutation in mitochondrial DNA. The defect can occur in one of a number of nuclear genes that control the maintenance, repair or supply of building blocks for mitochondrial DNA. Faults occur quite frequently in mitochondrial DNA, but are usually quickly corrected. If they are not corrected then breaks or “deletions” can occur. Currently mutations in three different genes (POLG 1, ANT 1and Twinkle ) are known to cause multiple deletions and are associated with a particular syndrome known as Chronic Progressive External Ophthalmoplegia Plus (CPEO+). Patients with this syndrome have difficulty with eye movement and drooping eyelids and in this respect are very similar to patients with single deletions. Complications with swallowing difficulties, heart problems, weakness and exercise intolerance may also occur. Additional problems include difficulty with balance and sometimes altered or absent sensation in the hands and feet.