Pathological study of progressive supranuclear palsy the cases with mutations in <scp><i>Bassoon</i></scp>

Clinical diagnosis of progressive supranuclear palsy (PSP) is difficult due to various phenotypes. Neuropathologically, PSP is defined by neuronal loss in the basal ganglia and brainstem with widespread occurrence of neurofibrillary tangles (NFTs) and accumulation of phosphorylated tau protein in neurons and glial cells in the brain. We previously identified the point mutation p.Pro3866Ala in the Bassoon (BSN) gene in a Japanese family with PSP-like syndrome. We newly detected BSN mutations in two autopsied PSP cases carrying p.Thr2542Met and p.Glu2759Gly, respectively. The case with p.Thr2542Met mutation showed neurological symptoms including behavioral abnormalities, cognitive dysfunction, and parkinsonism. Brain magnetic resonance imaging (MRI) showed atrophy of the midbrain tegmentum and hippocampus. Pathologically, moderate to severe loss of neurons with gliosis was also found in the substantia nigra, and there was an almost complete loss of neurons with gliosis in the transitional zone of the cornu ammonis (CA) 1 region to the subiculum. NFTs were observed in the globus pallidus, subthalamic nucleus, substantia nigra, and CA1. 4R tau-dominant tauopathy was detected. The case with p.Glu2759Gly mutation showed neurological symptoms, including right-dominant motor impairment, right limping gait, postural instability, and cognitive dysfunction. Brain MRI showed mild atrophy of the midbrain tegmentum and left-dominant parietal lobe atrophy. Pathologically, NFTs were detected in the globus pallidus, subthalamic nucleus, substantia nigra, thalamus, putamen, and brainstem tegmentum. Most neurons were immunopositive for four-repeat tau, whereas only a few of them harbored three-repeat tau-positive NFTs in the hippocampus. We showed the results of a pathological study of PSP cases with BSN mutations; these were two new cases. The clinical phenotypes were similar to the first case in the point of neurological symptoms. Accumulation of four-repeat tau was dominant. Further autopsies of BSN mutation cases and further elucidation of the molecular biological mechanism are desirable.