Dystrophy is defined as the process and consequences of hereditary progressive affections of specific cells in one or more tissues that initially show a normal function. The term abiotrophy was previously applied to these lesions, but has gone out of use. Degeneration is an equivocal term used for both acquired and hereditary disorders. Aging may or may not be considered as dystrophy. Dysplasias or dyshistogeneses are different from dystrophies. Dyshistogenetic tissues present with abnormal structure and function at birth in contrast to dystrophies, which are genetically programmed for later onset.