Patients with FUS mutations develop cytoplasmic FUS immunoreactive inclusions in lower motor neurons. Antibody to FUS immunolabels inclusions within the anterior horn (dotted line) of the spinal cord in patients with FUS mutations (A to F and arrowheads in O). Staining in controls (G, H, and M), mutant SOD1 FALS (I and J), and SALS (K, L, and N) demonstrate diffuse nuclear staining (arrows) with variable intensity without inclusions. Scale bars, 12 μm [(A) to (L)], 50 μm [(M) to (O)].