Beisha Tang

Identification of PRRT2 as the causative gene of paroxysmal kinesigenic dyskinesias

Paroxysmal kinesigenic dyskinesias is a paroxysmal movement disorder characterized by recurrent, brief attacks of abnormal involuntary movements induced by sudden voluntary movements. Although several loci, including the pericentromeric region of chromosome 16, have been linked to paroxysmal kinesigenic dyskinesias, the causative gene has not yet been identified. Here, we identified proline-rich transmembrane protein 2 (PRRT2) as a causative gene of paroxysmal kinesigenic dyskinesias by using a combination of exome sequencing and linkage analysis. Genetic linkage mapping with 11 markers that encompassed the pericentromeric of chromosome 16 was performed in 27 members of two families with autosomal dominant paroxysmal kinesigenic dyskinesias. Then, the whole-exome sequencing was performed in three patients from these two families. By combining the defined linkage region (16p12.1–q12.1) and the results of exome sequencing, we identified an insertion mutation c.649_650InsC (p.P217fsX7) in one family and a nonsense mutation c.487C>T (p.Q163X) in another family. To confirm our findings, we sequenced the exons and flanking introns of PRRT2 in another three families with paroxysmal kinesigenic dyskinesias. The c.649_650InsC (p.P217fsX7) mutation was identified in two of these families, whereas a missense mutation, c.796C>T (R266W), was identified in another family with paroxysmal kinesigenic dyskinesias. All of these mutations completely co-segregated with the phenotype in each family. None of these mutations was identified in 500 normal unaffected individuals of matched geographical ancestry. Thus, we have identified PRRT2 as the first causative gene of paroxysmal kinesigenic dyskinesias, warranting further investigations to understand the pathogenesis of this disorder.

Direct Conversion of Normal and Alzheimer’s Disease Human Fibroblasts into Neuronal Cells by Small Molecules

Neuronal conversion from human fibroblasts can be induced by lineage-specific transcription factors; however, the introduction of ectopic genes limits the therapeutic applications of such induced neurons (iNs). Here, we report that human fibroblasts can be directly converted into neuronal cells by a chemical cocktail of seven small molecules, bypassing a neural progenitor stage. These human chemical-induced neuronal cells (hciNs) resembled hiPSC-derived neurons and human iNs (hiNs) with respect to morphology, gene expression profiles, and electrophysiological properties. This approach was further applied to generate hciNs from familial Alzheimers disease patients. Taken together, our transgene-free and chemical-only approach for direct reprogramming of human fibroblasts into neurons provides an alternative strategy for modeling neurological diseases and for regenerative medicine.

Small heat-shock protein 22 mutated in autosomal dominant Charcot-Marie-Tooth disease type 2L

Charcot-Marie-Tooth (CMT) disease is the most common inherited motor and sensory neuropathy. We have previously described a large Chinese CMT family and assigned the locus underlying the disease (CMT2L; OMIM 608673) to chromosome 12q24. Here, we report a novel c.423G→T (Lys141Asn) missense mutation of small heat-shock protein 22-kDa protein 8 (encoded by HSPB8), which is also responsible for distal hereditary motor neuropathy type (dHMN) II. No disease-causing mutations have been identified in another 114 CMT families.

Dispensable role of Drosophila ortholog of LRRK2 kinase activity in survival of dopaminergic neurons

BackgroundParkinsons disease (PD) is the most prevalent incurable neurodegenerative movement disorder. Mutations in LRRK2 are associated with both autosomal dominant familial and sporadic forms of PD. LRRK2 encodes a large putative serine/threonine kinase with GTPase activity. Increased LRRK2 kinase activity plays a critical role in pathogenic LRRK2 mutant-induced neurodegeneration in vitro. Little is known about the physiological function of LRRK2.ResultsWe have recently identified a Drosophila line with a P-element insertion in an ortholog gene of human LRRK2 (dLRRK). The insertion results in a truncated Drosophila LRRK variant with N-terminal 1290 amino acids but lacking C-terminal kinase domain. The homozygous mutant fly develops normally with normal life span as well as unchanged number and pattern of dopaminergic neurons. However, dLRRK mutant flies were selectively sensitive to hydrogen peroxide induced stress but not to paraquat, rotenone and β-mercaptoethanol induced stresses.ConclusionOur results indicate that inactivation of dLRRK kinase activity is not essential for fly development and suggest that inhibition of LRRK activity may serve as a potential treatment of PD. However, dLRRK kinase activity likely plays a role in protecting against oxidative stress.

Identification of TMEM230 mutations in familial Parkinson's disease

Parkinsons disease is the second most common neurodegenerative disorder without effective treatment. It is generally sporadic with unknown etiology. However, genetic studies of rare familial forms have led to the identification of mutations in several genes, which are linked to typical Parkinsons disease or parkinsonian disorders. The pathogenesis of Parkinsons disease remains largely elusive. Here we report a locus for autosomal dominant, clinically typical and Lewy body–confirmed Parkinsons disease on the short arm of chromosome 20 (20pter-p12) and identify TMEM230 as the disease-causing gene. We show that TMEM230 encodes a transmembrane protein of secretory/recycling vesicles, including synaptic vesicles in neurons. Disease-linked TMEM230 mutants impair synaptic vesicle trafficking. Our data provide genetic evidence that a mutant transmembrane protein of synaptic vesicles in neurons is etiologically linked to Parkinsons disease, with implications for understanding the pathogenic mechanism of Parkinsons disease and for developing rational therapies.

Mutation Analysis of the Small Heat Shock Protein 27 Gene in Chinese Patients With Charcot-Marie-Tooth Disease

BACKGROUND Charcot-Marie-Tooth (CMT) disease, the most common hereditary peripheral neuropathy, is highly clinically and genetically heterogeneous, and mutations in at least 18 genes have been identified. Recently, mutations in small heat shock protein 27 (Hsp27) were reported to cause CMT disease type 2F and distal hereditary motor neuropathy. OBJECTIVE To investigate the frequency and phenotypic features of an Hsp27 mutation in Chinese patients with CMT disease. DESIGN DNA samples from 114 unrelated patients with CMT disease were screened for mutations in Hsp27 by polymerase chain reaction and direct sequencing. A cosegregated study was performed using the MbiI restriction endonuclease, and 50 healthy control subjects were analyzed. Haplotype analysis was performed using 5 short tandem repeat markers to analyze whether the families with the same mutation probably had a common ancestor. RESULTS One missense mutation, C379T, was detected in 4 autosomal dominant families with CMT disease type 2, and haplotype analysis indicated that the 4 families probably had a common founder. The frequency of the Hsp27 mutation is 0.9% (1/111) in Chinese patients with CMT disease in our study, and the phenotypes were characterized by later onset (age, 35-60 years) and mild sensory impairments. Electrophysiological findings showed moderately to severely slowed nerve conduction velocities in lower limb nerves but normal or mildly reduced velocities in upper limb nerves. CONCLUSIONS To our knowledge, this is the first report of an Hsp27 mutation in the Peoples Republic of China. The C379T mutation in Hsp27 also causes CMT disease type 2, except for distal hereditary motor neuropathy, and the phenotypes are distinct from the family with CMT disease type 2F described previously. A mutation of Hsp27 may be uncommon in Chinese patients with CMT disease.

Mutation analysis of Parkin, PINK1, DJ-1 and ATP13A2 genes in Chinese patients with autosomal recessive early-onset Parkinsonism

Autosomal recessive early‐onset Parkinsonism (AREP) has been associated with mutations in the Parkin, PINK1, DJ‐1, and ATP13A2 genes. We studied the prevalence of mutations in all four genes in 29 Chinese unrelated families with AREP using direct sequencing analysis and real‐time quantitative PCR analysis assay. There are 14 families (48.3%) with mutations of Parkin gene, 2 families (6.9%) with mutations of PINK1 gene, and 1 family (3.4%) with mutation of DJ‐1 gene. No pathogenic mutations in ATP13A2 gene were found in these families. Three Parkin gene mutations (c.G859T, c.1069‐1074delGTGTCC, and c.T1422C) and one DJ‐1 gene mutation (c.T29C) have not been reported previously. In conclusion, Parkin gene mutation is the most common pathogenic factor in Chinese patients with AREP. Mutations of DJ‐1 and PINK1 gene are also found in Chinese families with AREP. Mutations in ATP13A2 gene may be rare in Chinese families with AREP.

Clinical profiles of Parkinson's disease associated with common leucine-rich repeat kinase 2 and glucocerebrosidase genetic variants in Chinese individuals

Clinical profiles of Parkinsons disease (PD) related to LRRK2 (LRRK2-PD), and GBA (GBA-PD) genes have not been reported in Chinese individuals. In this study, we have investigated motor and non-motor aspects in 1638 Chinese PD patients who carried LRRK2 G2385R or R1628P (LRRK2-PD, n = 223), GBA L444P variant (GBA-PD, n = 49), or none of the variants (idiopathic PD [IPD], n = 1366). As a result, age at onset and motor and non-motor features of LRRK2-PD patients were similar to IPD patients except for milder non-motor symptoms. In contrast, GBA-PD patients had a significantly younger age at onset and higher Unified Parkinsons Disease Rating Scale scores than LRRK2-PD and IPD patients. In addition, postural instability and gait disorders, motor complications, cognitive decline, hallucination, sexual dysfunction, and constipation were more frequent in GBA-PD than in LRRK2-PD and IPD patients, and GBA-PD patients had a worse performance for social functioning and role-emotional scores. Our study represents the first large-scale clinical study of LRRK2-PD and GBA-PD in ethnic Chinese individuals. The data suggest that both LRRK2-PD and GBA-PD are similar to IPD, except for an earlier age at onset and relatively more common non-motor symptoms in GBA-PD patients. These findings strengthen our understanding of the clinical heterogeneity of PD, and may have implications for molecular classification of the disease.

PLA2G6 gene mutation in autosomal recessive early-onset parkinsonism in a Chinese cohort

Objective: Mutations in the PLA2G6 gene at the PARK14 locus have been reported in complicated parkinsonism. To assess the prevalence of and phenotypes associated with PLA2G6 gene mutations, we screened PLA2G6 mutations in a cohort of patients with autosomal recessive early-onset parkinsonism (AREP). Methods: We selected 12 families with AREP in which the Parkin, PINK1, DJ-1, ATP13A2, and FBXO7 gene mutations had been previously excluded. All patients came from the mainland of China. The entire PLA2G6 coding region and exon-intron boundaries were sequenced from genomic DNA templates. We then performed PET studies on individuals in the pedigree with a homozygous PLA2G6 mutation, and investigated the enzyme activity level of the mutation. Results: A homozygous missense mutation, c.G991T (p.D331Y), was identified in an autosomal recessive case. A younger sister of the p.D331Y-carrying patient was also homozygous for the mutation, but with no extrapyramidal symptoms. A PET study showed a substantial reduction in dopamine transporter (DAT) binding in the p.D331Y patient, and a slight reduction in DAT binding in his sister. In vitro, we experimentally demonstrate that the D331Y mutation caused an approximately 70%reduction in enzyme activity. Conclusions: We have confirmed that the PLA2G6 gene allocated PARK14 locus and is associated with AREP.

Sodium Valproate Alleviates Neurodegeneration in SCA3/MJD via Suppressing Apoptosis and Rescuing the Hypoacetylation Levels of Histone H3 and H4

Spinocerebellar ataxia type 3 (SCA3) also known as Machado-Joseph Disease (MJD), is one of nine polyglutamine (polyQ) diseases caused by a CAG-trinucelotide repeat expansion within the coding sequence of the ATXN3 gene. There are no disease-modifying treatments for polyQ diseases. Recent studies suggest that an imbalance in histone acetylation may be a key process leading to transcriptional dysregulation in polyQ diseases. Because of this possible imbalance, the application of histone deacetylase (HDAC) inhibitors may be feasible for the treatment of polyQ diseases. To further explore the therapeutic potential of HDAC inhibitors, we constructed two independent preclinical trials with valproic acid (VPA), a promising therapeutic HDAC inhibitor, in both Drosophila and cell SCA3 models. We demonstrated that prolonged use of VPA at specific dose partly prevented eye depigmentation, alleviated climbing disability, and extended the average lifespan of SCA3/MJD transgenic Drosophila. We found that VPA could both increase the acetylation levels of histone H3 and histone H4 and reduce the early apoptotic rate of cells without inhibiting the aggregation of mutant ataxin-3 proteins in MJDtr-Q68- expressing cells. These results collectively support the premise that VPA is a promising therapeutic agent for the treatment of SCA3 and other polyQ diseases.