Abstract

Molecular pathology has identified 2 distinct forms of neuronal inclusion body in Amyotrophic Lateral Sclerosis (ALS). ALS-type inclusions are skeins or small dense filamentous aggregates which can only be demonstrated by ubiquitin immunocytochemistry (ICC). In contrast hyaline conglomerates (HC) are large multifocal accumulations of neurofilaments. Previous reports have failed to clarify the distinction and relationship between these inclusions. Correlation of molecular pathology with sporadic and familial cases of ALS will detect specific associations between molecular lesions and defined genetic abnormalities; and determine the relevance of molecular events in familial cases to the pathogenesis of sporadic disease. We describe the molecular pathology of 5 ALS cases linked to abnormalities of the SOD1 gene, in comparison with a series of 73 sporadic cases in which SOD1-gene abnormalities were excluded. Hyaline conglomerate inclusions were detected only in the 2 cases with the SOD1 I113T mutation and showed a widespread multisystem distribution. In contrast ALS-type inclusions characterized sporadic cases (70/73) and were restricted to lower motor neurons. Hyaline conglomerates were not seen in sproadic cases. Confocal microscopic analysis and ICC shows that HC contain equally abundant phosphorylated and nonphosphorylated neurofilament epitopes, indicating that phosphorylation is not essential for their formation. In contrast neurofilament immunoreactivity is virtually absent from typical ALS-type inclusions. The SOD1-related cases all had marked corticospinal tract and dorsal column myelin loss. In 4 cases the motor cortex was normal or only minimally affected. This further illustrates the extent to which upper motor neuron damage in ALS is usually a distal axonopathy. Previously reported pathological accounts of SOD1-related familial ALS (FALS) are reviewed. Hyaline conglomerates are so far described in cases with mutations A4V, I113T and H48Q. In only 1 of 12 cases (H48Q) reported were both HC and ALS-type inclusions present in the same case. These findings suggest the possibility that the molecular pathology of neuronal inclusions in ALS indicates 2 distinct pathogenetic cascades.

Author notes

This work was supported by grants from the Wellcome Trust and by MRC UK direct support.