TYMP and progressive external ophthalmoplegia: Intracellular TYMP acts a cytosolic enzyme that is essential for the stability of mitochondrial DNA, and gene mutations cause mitochondrial neurogastrointestinal encephalomyopathy associated with ptosis and progressive external ophthalmoplegia, peripheral neuropathy, severe gastrointestinal dysmotility, cachexia and leukoencephalopathy.28