The various nervous and mental diseases which show a familial tendency or in which hereditary factors are suspected, are difficult to classify, partly because of group overlapping and partly because the character of the pathologic lesions is often closely comparable in two processes which are quite divergent from the clinical standpoint. An example of the first tendency is the occurrence of cases of hereditary ataxia combining both clinically and anatomically the features of both the Friedreich and the Marie types. An example of the second point may be mentioned in the great similarity of the atrophic process involving the cells of the upper motor neuron in spastic paraplegia and that in the cells of the lower motor neuron in progressive spinal muscular atrophy.
It is obvious that the clinical picture will not be determined by either the nature of the pathologic process or its anatomic locus, but by a combination
ORTON ST. THE PATHOLOGY OF THE HEREDITARY AND FAMILIAL NERVOUS AND MENTAL DISEASES. Arch NeurPsych. 1925;13(1):96–115. doi:10.1001/archneurpsyc.1925.02200070099008
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