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A 21-nucleotide duplication in one allele of SNCA was identified in a previously described disease with abundant α-synuclein inclusions that we now call juvenile-onset synucleinopathy (JOS). This mutation translates into the insertion of MAAAEKT after residue 22 of α-synuclein, resulting in a protein of 147 amino acids. Both wild-type and mutant proteins were present in sarkosyl-insoluble material that was extracted from frontal cortex of the individual with JOS and examined by electron cryo-microscopy. The structures of JOS filaments, comprising either a single protofilament, or a pair of protofilaments, revealed a new α-synuclein fold that differs from the folds of Lewy body diseases and multiple system atrophy (MSA). The JOS fold consists of a compact core, the sequence of which (residues 36–100 of wild-type α-synuclein) is unaffected by the mutation, and two disconnected density islands (A and B) of mixed sequences. There is a non-proteinaceous cofactor bound between the core and island A. The JOS fold resembles the common substructure of MSA Type I and Type II dimeric filaments, with its core segment approximating the C-terminal body of MSA protofilaments B and its islands mimicking the N-terminal arm of MSA protofilaments A. The partial similarity of JOS and MSA folds extends to the locations of their cofactor-binding sites. In vitro assembly of recombinant wild-type α-synuclein, its insertion mutant and their mixture yielded structures that were distinct from those of JOS filaments. Our findings provide insight into a possible mechanism of JOS fibrillation in which mutant α-synuclein of 147 amino acids forms a nucleus with the JOS fold, around which wild-type and mutant proteins assemble during elongation.

We report a family of Japanese origin that has five individuals from two generations affected by an illness characterized by dementia, a stooped posture and an antiflexion gait with an onset in the fourth or fifth decade of life. Two siblings had a clinical phenotype characterized by dementia and Parkinsonism with stooped posture, rigidity and bradykinesia. Neuropathological alterations in both patients included numerous 'cotton wool' plaques (CWPs), senile plaques, severe amyloid angiopathy, neurofibrillary tangles, neuronal rarefaction and gliosis. CWPs were present throughout the cerebral cortex as well as in the caudate nucleus, putamen, claustrum, thalamus, substantia innominata and colliculi. These plaques contained a small quantity of argyrophilic and tau-immunopositive neurites as well as glial fibrillary acidic protein-immunopositive elements. They were mildly fluorescent with thioflavin S and immunopositive using monoclonal antibodies recognizing amyloid beta (A beta) ending at residue 42. The main constituents of CWPs were neuropil elements and extracellular amyloid fibrils. These neuropil elements were small dendrites including spines, axon terminals containing synaptic vesicles and astrocytic processes. Dendrites occasionally contained bundles of paired helical filaments. Dendrites and axons often had an irregular outline and appeared as degenerating osmiophilic processes containing electron-dense mitochondria. Genetic analysis of the proband's affected sibling revealed a novel nucleotide substitution (G to A) in exon 8 of the Presenilin 1 ( PSEN1) gene. This nucleotide change results in a glycine to aspartic acid substitution at residue 217 of the PSEN1 protein. This study provides further evidence of clinical and pathological heterogeneity in dementing illnesses associated with PSEN1 mutations.

REM sleep behavior disorder (RBD) is known to be observed more frequently in patients with an α-synucleinopathy such as Parkinson’s disease (PD) than in the general population. The precise prevalence of RBD in Japanese PD patients is not known. Therefore, we investigated the prevalence and the clinical characteristics of patients with RBD in a large population of Japanese patients with PD. We investigated various clinical features and employed the Japanese version of the RBD screening questionnaire on 469 non-demented Japanese PD patients in this multicenter study. Probable or possible RBD was detected in 146 patients (31.1%) and was significantly associated with longer PD duration, higher Hoehn and Yahr stage, higher Unified Parkinson’s Disease Rating Scale part III subscale (7 items), more motor fluctuations, and a higher levodopa-equivalent daily dose ( p  < 0.01). As to the major autonomic dysfunctions, severe constipation was significantly more frequent in PD patients with RBD than in those without it ( p  < 0.01). The RBD symptoms of 53 patients (39.0%) preceded the onset of PD motor symptoms. The median interval from the onset of RBD symptoms to PD motor symptoms was 17.5 years, and 3 patients had intervals of over 50 years. This large-scale multicenter study revealed that RBD is a frequent non-motor symptom in Japanese patients with PD, which may precede the onset of motor symptoms. Moreover, RBD that increases with the duration and severity of PD may be associated with autonomic dysfunction.

Pure red cell aplasia (PRCA) is well known to be concomitant with myasthenia gravis (MG), but it is difficult to predict the development of PRCA in patients with MG. Of 135 patients with MG, four (2.9%) had PRCA. All patients developed PRCA after thymectomy during a period when MG was in remission. The frequencies of thymoma, bulbar involvement and high anti-acetylcholine receptor (AChR) antibody levels were significantly higher in four patients with PRCA. Japanese MG patients with these characteristics at presentation were at significant risk for the development of PRCA after thymectomy.

A 44-year-old Japanese man with elevated growth hormone levels and gradual deterioration of mental and renal function was admitted to the hospital. With his deteriorated general condition and renal failure, the patient developed pulmonary thromboembolism and died of respiratory failure. Autopsy examination was conducted, which revealed abnormal accumulation or intracytoplasmic storage of lipid-rich material in the small blood vessels, kidney, heart, and nervous system. After postmortem pathologic studies, including light-microscopic histochemistry, electron microscopy, and biochemical analysis of the stored lipid contents, a final diagnosis of Fabry disease was made. Histopathologic examination revealed a unique vasculopathy characterized by the presence of abnormal intracytoplasmic lipid inclusions and vascular remodeling. With regard to the clinical presentation of acromegaly, hyperplasia but not adenomatous transformation of the acidophils of the anterior pituitary gland with immunohistochemical detection of growth hormone within the cells was noted. In this case, the complication of acromegaly with hyperplasia of the acidophilic cells of the anterior pituitary gland and the unique vasculopathy causing significant organ failure, mainly of the kidney, heart, and central nervous systems, possibly as a result of microcirculatory failure, are considered to be not incidental findings but to be intimately involved in the pathogenesis of Farby disease.

A 21-nucleotide duplication in one allele of SNCA was identified in a previously described disease with abundant α-synuclein inclusions that we now call juvenile-onset synucleinopathy (JOS). Both wild-type α-synuclein and its insertion mutant containing seven additional residues (MAAAEKT) after residue 22 were present in sarkosyl-insoluble material that was extracted from frontal cortex of the individual with JOS and examined by electron cryo-microscopy. The structures of JOS filaments, comprising either a single protofilament, or a pair of protofilaments, revealed a new α-synuclein fold that differs from the folds of Lewy body diseases and multiple system atrophy (MSA). The JOS fold consists of a compact core, the sequence of which (residues 36-100 of wild-type α-synuclein) is unaffected by the mutation, and two disconnected density islands (A and B) of mixed sequences. There is a non-proteinaceous cofactor bound between the core and island A. The JOS fold resembles the common substructure of MSA type I and type II dimeric filaments, with its core segment approximating the C-terminal body of MSA protofilaments B and its islands mimicking the N-terminal arm of MSA protofilaments A. The partial similarity of JOS and MSA folds extends to the locations of their cofactor-binding sites. Our findings provide insight into a likely mechanism of JOS fibrillation in which mutant α-synuclein of 147 amino acids forms a nucleus with the JOS fold, around which wild-type and mutant proteins assemble during elongation.Competing Interest StatementThe authors have declared no competing interest.