Ubap1 knock-in mice reproduced the phenotype of SPG80.

SPG80 is a neurodegenerative disorder characterized by a pure type of juvenile-onset hereditary spastic paraplegia and is caused by a heterozygous mutation of the UBAP1 (ubiquitin-associated protein 1) gene. UBAP1 is one of the subunits of the endosomal sorting complex required for transport I and plays a role in endosome sorting by binding to ubiquitin-tagged proteins. In this study, we generated novel Ubap1+/E176Efx23 knock-in mice, in which the SOUBA domain of Ubap1 was completely deleted with the UMA domain being intact, as an animal model of SPG80. The knock-in mice with this heterozygous Ubap1 truncated mutation appeared normal at birth, but they developed progressive hind limb dysfunction several months later. Molecular pathologically, loss of neurons in the spinal cord and accumulation of ubiquitinated proteins were observed in Ubap1+/E176Efx23 knock-in mice. In addition, changes in the distributions of Rab5 and Rab7 in the spinal cord suggest that this mutation in Ubap1 disturbs endosome-mediated vesicular trafficking. This is the first report of a mouse model that reproduces the phenotype of SPG80. Our knock-in mice may provide a clue for understanding the molecular pathogenesis underlying UBAP1-related HSP and screening of therapeutic agents.

RFC1 repeat expansion in Japanese patients with late-onset cerebellar ataxia.

Recently, the expansion of an intronic AAGGG repeat in the replication factor C subunit 1 (RFC1) gene was reported to cause cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS). In Europeans, the expansion accounted for 22% of sporadic patients with late-onset ataxia. We genotyped 37 Japanese patients comprising 25 familial (autosomal recessive or undecided transmission) and 12 sporadic ones with late-onset ataxia. We found intronic repeat expansions in RFC1 in three (12%) of the familial patients and one (8.5%) of the sporadic ones. Although our cohort study was small, the disease frequency in Japanese patients with CANVAS might be lower than that in European ones. In addition, we found biallelic ACAGG repeat expansion in one patient, indicating ACAGG repeat expansion might cause CANVAS. Clinically, we found one patient with sleep apnea syndrome, which has not been reported previously. Thus, this study might expand the clinical and genetic spectrum of CANVAS.

Clinical and Genetic Study of the First Japanese FTDP-17 Patient with a Mutation of +3 in Intron 10 in the MAPT Gene.

Frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17) with mutations in the MAPT gene is a hereditary neurodegenerative tauopathy with various clinical phenotypes. We herein report the first Japanese patient with FTDP-17 caused by an IVS10+3G>A mutation in the MAPT gene, which is linked to an H1M haplotype. The present study suggests that the IVS10+3G>A mutation in the MAPT gene can have originated from a non-Caucasian population. In the disease course, myoclonus and respiratory failure can be observed. This study may expand on the clinical and genetic findings for FTDP-17 with mutations in the MAPT gene.

Exome Sequencing Reveals a Novel Homozygous Frameshift Mutation in the CYP7B1 Gene in a Japanese Patient with SPG5.

SPG5 is a rare subtype of autosomal recessive hereditary spastic paraplegia caused by a homozygous mutation in the oxysterol 7α-hydroxylase gene, CYP7B1. We describe the first Japanese patient with SPG5 with a novel mutation in the CYP7B1 gene. On exome sequencing, we identified a homozygous frameshift mutation, c.741delA, p.K247fs, in exon 3 of the CYP7B1 gene. The patient showed spastic paraparesis with white matter hyperintensities in the bilateral corona radiata and periventricular and subcortical regions on brain magnetic resonance imaging. The present study expands the mutation spectrum of CYP7B1 and provides an opportunity to study the genotype-phenotype correlation in SPG5.