A Japanese patient with familial ALS and a p.K510M mutation in the gene for FUS (FUS) resulting in the totally locked-in state

We describe a Japanese patient with familial amyotrophic lateral sclerosis (ALS) and a p.K510M mutation in the fused in sarcoma gene (FUS). The patient's condition was characterized clinically by an early onset and rapid progression. The patient eventually required mechanical ventilation and progressed to the totally locked-in state. Neuropathologically, multiple system degeneration with many FUS-immunoreactive structures was observed. The involvement of the globus pallidus, subthalamic nucleus, substantia nigra, cerebellar efferent system, and both upper and lower motor neurons in the present patient was comparable to that described for ALS patients with different mutations in FUS, all of whom progressed to the totally locked-in state. However, the patient also exhibited degeneration of the cerebellar afferent system and posterior column. Furthermore, the appearance of non-compact FUS-immunoreactive neuronal cytoplasmic inclusions and many FUS-immunoreactive glial cytoplasmic inclusions were unique to the present patient. These features suggest that the morphological characteristics of the FUS-immunoreactive structures and distribution of the lesions vary with the diversity of mutations in FUS.