Identical mitochondrial DNA deletion in mother with progressive external ophthalmoplegia and son with Pearson marrow-pancreas syndrome.

We describe a family in which the mother has progressive external ophthalmoplegia with the common 4977 base pair deletion, and her son has a syndrome similar to the Pearson marrow-pancreas syndrome with the identical deletion. This case extends the clinical phenotype of the Pearson syndrome and raises the possibility that developmentally regulated tissue-specific nuclear factors are responsible for the differential phenotypic expression of these two mitochondrial disorders.