Somatic mutation: a cause of sporadic neurodegenerative diseases?

The major causes of the common neurodegenerative diseases remain unknown. Alzheimer's disease, Parkinson's disease and motor neuron disease occur in both sporadic and familial forms, and mutations are progressively being found in families with these disorders. However, attempts to find causative mutations in blood DNA from the sporadic forms of the diseases have proved fruitless. It is hypothesised that this is because the causative mutations are found only in the cells in the central nervous system that are affected by the disease. These mutations arise in the developing embryo in progenitor cells of neurons or glia. The diseases are not passed to offspring since the mutations are not present in the germ-line. To find somatic mutations, the affected central nervous system cells need to be separated out and submitted to DNA analysis.