[The implications of TDP-43 mutations in pathogenesis of amyotrophic lateral sclerosis]

The molecular pathogenesis of amyotrophic lateral sclerosis (ALS) is unclear. TAR DNA-binding proteins of 43 kDa (TDP-43) -positive-cytoplasmic inclusions have been found in the glia and neurons of ALS patients. TDP-43 -positive inclusions have been reported in several neurodegenerative disorders other than ALS. Therefore it is not clear whether TDP-43 plays a primary role in the pathogenesis of ALS. The discovery of TDP-43 mutations in ALS patients indicates that TDP-43 plays a pivotal role in the pathogenesis of ALS. More than 30 mutations in the TDP-43 gene have been identified in patients with familial and sporadic ALS. ALS with a TDP-43 mutation is classified as ALS-10. The clinical features of ALS-10 are quite similar to those of sporadic ALS. Furthermore, the neuropathological findings for ALS-10, including TDP-43 -positive inclusions and Bunina bodies, are identical to those in sporadic ALS; these findings indicate that the study of ALS-10 may lead to a better understanding of sporadic ALS. Most of the mutations are located in the C-terminus of TDP-43, which may function as a binding domain for heterogeneous nuclear ribonucleoprotein. Biochemical analyses of TDP-43 in sporadic ALS patients indicate that the TDP-43 is truncated, and the C-terminus is phosphorylated forming insoluble inclusions in the neurons and glia. In certain ALS-10 cases, missense mutated TDP-43s tend to be truncated and form inclusions. The cytotoxicity of these mutated TDP-43s has also been reported; however, these results are still controversial. Therefore, further analysis is required to elucidate the molecular mechanism underlying the development of ALS-10.