Presence of different characteristics, in contrast to homogeneity, in which characteristics are the same in each sample or case. One of the key challenges in identifying the causes of, and designing effective treatments for, Parkinson’s disease is its heterogeneous nature: Although there are common symptoms that nearly everyone who has the disease experiences, the combinations and progression of those symptoms make the course of disease uniquely individual. It is not much of an exaggeration to say that no two people with Parkinson’s have the same experience of the disease.
Within the context of gene mutations, Parkinson’s disease is also considered heterogeneous because any of several known mutations may be present. As well, none of these mutations is specific to Parkinson’s disease; all can be found, singly or in differing combinations, in other neu-romuscular disorders. The alpha-synuclein gene mutation is present in lewy body disease, for example. Whether this means there are as yet unknown connections among these disorders or the mutations have broad-based implications is one of the many dimensions that researchers continue to explore. Scientists are fairly certain that other genes that contribute to the development of Parkinson’s are not far from being discovered and hope that these discoveries will lead to an understanding of how the various genetic factors shape Parkinson’s.