A Mutation in VPS35, Encoding a Subunit of the Retromer Complex, Causes Late-Onset Parkinson Disease

To identify rare causal variants in late-onset Parkinson disease (PD), we investigated an Austrian family with 16 affected individuals by exome sequencing. We found a missense mutation, c.1858G>A (p.Asp620Asn), in the VPS35 gene in all seven affected family members who are alive. By screening additional PD cases, we saw the same variant cosegregating with the disease in an autosomal-dominant mode with high but incomplete penetrance in two further families with five and ten affected members, respectively. The mean age of onset in the affected individuals was 53 years. Genotyping showed that the shared haplotype extends across 65 kilobases around VPS35. Screening the entire VPS35 coding sequence in an additional 860 cases and 1014 controls revealed six further nonsynonymous missense variants. Three were only present in cases, two were only present in controls, and one was present in cases and controls. The familial mutation p.Asp620Asn and a further variant, c.1570C>T (p.Arg524Trp), detected in a sporadic PD case were predicted to be damaging by sequence-based and molecular-dynamics analyses. VPS35 is a component of the retromer complex and mediates retrograde transport between endosomes and the trans-Golgi network, and it has recently been found to be involved in Alzheimer disease.     

Biallelic Mutations in the Autophagy Regulator DRAM2 Cause Retinal Dystrophy with Early Macular Involvement

Retinal dystrophies are an overlapping group of genetically heterogeneous conditions resulting from mutations in more than 250 genes. Here we describe five families affected by an adult-onset retinal dystrophy with early macular involvement and associated central visual loss in the third or fourth decade of life. Affected individuals were found to harbor disease-causing variants in DRAM2 (DNA-damage regulated autophagy modulator protein 2). Homozygosity mapping and exome sequencing in a large, consanguineous British family of Pakistani origin revealed a homozygous frameshift variant (c.140delG [p.Gly47Valfs^∗3]) in nine affected family members. Sanger sequencing of DRAM2 in 322 unrelated probands with retinal dystrophy revealed one European subject with compound heterozygous DRAM2 changes (c.494G>A [p.Trp165^∗] and c.131G>A [p.Ser44Asn]). Inspection of previously generated exome sequencing data in unsolved retinal dystrophy cases identified a homozygous variant in an individual of Indian origin (c.64_66del [p.Ala22del]). Independently, a gene-based case-control association study was conducted via an exome sequencing dataset of 18 phenotypically similar case subjects and 1,917 control subjects. Using a recessive model and a binomial test for rare, presumed biallelic, variants, we found DRAM2 to be the most statistically enriched gene; one subject was a homozygote (c.362A>T [p.His121Leu]) and another a compound heterozygote (c.79T>C [p.Tyr27His] and c.217_225del [p.Val73_Tyr75del]). DRAM2 encodes a transmembrane lysosomal protein thought to play a role in the initiation of autophagy. Immunohistochemical analysis showed DRAM2 localization to photoreceptor inner segments and to the apical surface of retinal pigment epithelial cells where it might be involved in the process of photoreceptor renewal and recycling to preserve visual function.     

Mutations in ROGDI Cause Kohlschütter-Tönz Syndrome

Kohlschütter-Tönz syndrome (KTS) is an autosomal-recessive disease characterized by the combination of epilepsy, psychomotor regression, and amelogenesis imperfecta. The molecular basis has not yet been elucidated. Here, we report that KTS is caused by mutations in ROGDI. Using a combination of autozygosity mapping and exome sequencing, we identified a homozygous frameshift deletion, c.229_230del (p.Leu77Alafs^∗64), in ROGDI in two affected individuals from a consanguineous family. Molecular studies in two additional KTS-affected individuals from two unrelated Austrian and Swiss families revealed homozygosity for nonsense mutation c.286C>T (p.Gln96^∗) and compound heterozygosity for the splice-site mutations c.531+5G>C and c.532-2A>T in ROGDI, respectively. The latter mutation was also found to be heterozygous in the mother of the Swiss affected individual in whom KTS was reported for the first time in 1974. ROGDI is highly expressed throughout the brain and other organs, but its function is largely unknown. Possible interactions with DISC1, a protein involved in diverse cytoskeletal functions, have been suggested. Our finding that ROGDI mutations cause KTS indicates that the protein product of this gene plays an important role in neuronal development as well as amelogenesis.     

A Founder Mutation in VPS11 Causes an Autosomal Recessive Leukoencephalopathy Linked to Autophagic Defects

Genetic leukoencephalopathies (gLEs) are a group of heterogeneous disorders with white matter abnormalities affecting the central nervous system (CNS). The causative mutation in ~50% of gLEs is unknown. Using whole exome sequencing (WES), we identified homozygosity for a missense variant, VPS11: c.2536T>G (p.C846G), as the genetic cause of a leukoencephalopathy syndrome in five individuals from three unrelated Ashkenazi Jewish (AJ) families. All five patients exhibited highly concordant disease progression characterized by infantile onset leukoencephalopathy with brain white matter abnormalities, severe motor impairment, cortical blindness, intellectual disability, and seizures. The carrier frequency of the VPS11: c.2536T>G variant is 1:250 in the AJ population (n = 2,026). VPS11 protein is a core component of HOPS (homotypic fusion and protein sorting) and CORVET (class C core vacuole/endosome tethering) protein complexes involved in membrane trafficking and fusion of the lysosomes and endosomes. The cysteine 846 resides in an evolutionarily conserved cysteine-rich RING-H2 domain in carboxyl terminal regions of VPS11 proteins. Our data shows that the C846G mutation causes aberrant ubiquitination and accelerated turnover of VPS11 protein as well as compromised VPS11-VPS18 complex assembly, suggesting a loss of function in the mutant protein. Reduced VPS11 expression leads to an impaired autophagic activity in human cells. Importantly, zebrafish harboring a vps11 mutation with truncated RING-H2 domain demonstrated a significant reduction in CNS myelination following extensive neuronal death in the hindbrain and midbrain. Thus, our study reveals a defect in VPS11 as the underlying etiology for an autosomal recessive leukoencephalopathy disorder associated with a dysfunctional autophagy-lysosome trafficking pathway.     

Endosome to Golgi Retrieval of the Vacuolar Protein Sorting Receptor, Vps10p, Requires the Function of the VPS29, VPS30, and VPS35 Gene Products

Mutations in the S. cerevisiae VPS29 and VPS30 genes lead to a selective protein sorting defect in which the vacuolar protein carboxypeptidase Y (CPY) is missorted and secreted from the cell, while other soluble vacuolar hydrolases like proteinase A (PrA) are delivered to the vacuole. This phenotype is similar to that seen in cells with mutations in the previously characterized VPS10 and VPS35 genes. Vps10p is a late Golgi transmembrane protein that acts as the sorting receptor for soluble vacuolar hydrolases like CPY and PrA, while Vps35p is a peripheral membrane protein which cofractionates with membranes enriched in Vps10p. The sequences of the VPS29, VPS30, and VPS35 genes do not yet give any clues to the functions of their products. Each is predicted to encode a hydrophilic protein with homologues in the human and C. elegans genomes. Interestingly, mutations in the VPS29, VPS30, or VPS35 genes change the subcellular distribution of the Vps10 protein, resulting in a shift of Vps10p from the Golgi to the vacuolar membrane. The route that Vps10p takes to reach the vacuole in a vps35 mutant does not depend upon Sec1p mediated arrival at the plasma membrane but does require the activity of the pre-vacuolar endosomal t-SNARE, Pep12p. A temperature conditional allele of the VPS35 gene was generated and has been found to cause missorting/secretion of CPY and also Vps10p to mislocalize to a vacuolar membrane fraction at the nonpermissive temperature. Vps35p continues to cofractionate with Vps10p in vps29 mutants, suggesting that Vps10p and Vps35p may directly interact. Together, the data indicate that the VPS29, VPS30, and VPS35 gene products are required for the normal recycling of Vps10p from the prevacuolar endosome back to the Golgi where it can initiate additional rounds of vacuolar hydrolase sorting.     

Interactions of the apolipoprotein A5 gene polymorphisms and alcohol consumption on serum lipid levels

Background

Little is known about the interactions of apolipoprotein (Apo) A5 gene polymorphisms and alcohol consumption on serum lipid profiles. The present study was undertaken to detect the interactions of ApoA5–1131T>C, c.553G>T and c.457G>A polymorphisms and alcohol consumption on serum lipid levels.

Methodology/Principal Findings

A total of 516 nondrinkers and 514 drinkers were randomly selected from our previous stratified randomized cluster samples. Genotyping was performed by polymerase chain reaction and restriction fragment length polymorphism. The levels of serum total cholesterol (TC), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), ApoA1 and ApoB were higher in drinkers than in nondrinkers (P<0.05–0.001). The genotypic and allelic frequencies of three loci were not different between the two groups. The interactions between –1131T>C genotypes and alcohol consumption on ApoB levels (P<0.05) and the ApoA1/ApoB ratio (P<0.01), between c.553G>T genotypes and alcohol consumption on low-density lipoprotein cholesterol (LDL-C) levels (P<0.05) and the ApoA1/ApoB ratio (P<0.05), and between c.457G>A genotypes and alcohol consumption on TG levels (P<0.001) were detected by factorial regression analysis after controlling for potential confounders. Four haplotypes (T-G-G, C-G-G, T-A-G and C-G-T) had frequencies ranging from 0.06 to 0.87. Three haplotypes (C-G-G, T-A-G, and C-G-T) were significantly associated with serum lipid parameters. The –1131T>C genotypes were correlated with TG, and c.553G>T and c.457G>A genotypes were associated with HDL-C levels in nondrinkers (P<0.05 for all). For drinkers, the –1131T>C genotypes were correlated with TC, TG, LDL-C, ApoB levels and the ApoA1/ApoB ratio (P<0.01 for all); c.553G>T genotypes were correlated with TC, TG, HDL-C and LDL-C levels (P<0.05–0.01); and c.457G>A genotypes were associated with TG, LDL-C, ApoA1 and ApoB levels (P<0.05–0.01).

Conclusions

The differences in some serum lipid parameters between the drinkers and nondrinkers might partly result from different interactions of the ApoA5 gene polymorphisms and alcohol consumption.     

Rare Primary Mitochondrial DNA Mutations and Probable Synergistic Variants in Leber's Hereditary Optic Neuropathy

Background

Leber’s hereditary optic neuropathy (LHON) is a maternally inherited blinding disorder, which in over 90% of cases is due to one of three primary mitochondrial DNA (mtDNA) point mutations (m.11778G>A, m.3460G>A and m.14484T>C, respectively in MT-ND4, MT-ND1 and MT-ND6 genes). However, the spectrum of mtDNA mutations causing the remaining 10% of cases is only partially and often poorly defined.

Methodology/Principal Findings

In order to improve such a list of pathological variants, we completely sequenced the mitochondrial genomes of suspected LHON patients from Italy, France and Germany, lacking the three primary common mutations. Phylogenetic and conservation analyses were performed. Sixteen mitochondrial genomes were found to harbor at least one of the following nine rare LHON pathogenic mutations in genes MT-ND1 (m.3700G>A/p.A132T, m.3733G>A-C/p.E143K-Q, m.4171C>A/p.L289M), MT-ND4L (m.10663T>C/p.V65A) and MT-ND6 (m.14459G>A/p.A72V, m.14495A>G/p.M64I, m.14482C>A/p.L60S, and m.14568C>T/p.G36S). Phylogenetic analyses revealed that these substitutions were due to independent events on different haplogroups, whereas interspecies comparisons showed that they affected conserved amino acid residues or domains in the ND subunit genes of complex I.

Conclusions/Significance

Our findings indicate that these nine substitutions are all primary LHON mutations. Therefore, despite their relative low frequency, they should be routinely tested for in all LHON patients lacking the three common mutations. Moreover, our sequence analysis confirms the major role of haplogroups J1c and J2b (over 35% in our probands versus 6% in the general population of Western Europe) and other putative synergistic mtDNA variants in LHON expression.     

Ficolin-2 levels and FCN2 haplotypes influence hepatitis B infection outcome in Vietnamese patients

Human Ficolin-2 (L-ficolins) encoded by FCN2 gene is a soluble serum protein that plays an important role in innate immunity and is mainly expressed in the liver. Ficolin-2 serum levels and FCN2 single nucleotide polymorphisms were associated to several infectious diseases. We initially screened the complete FCN2 gene in 48 healthy individuals of Vietnamese ethnicity. We genotyped a Vietnamese cohort comprising of 423 clinically classified hepatitis B virus patients and 303 controls for functional single nucleotide polymorphisms in the promoter region (-986G>A, -602G>A, -4A>G) and in exon 8 (+6424G>T) by real-time PCR and investigated the contribution of FCN2 genotypes and haplotypes to serum Ficolin-2 levels, viral load and liver enzyme levels. Haplotypes differed significantly between patients and controls (P = 0.002) and the haplotype AGGG was found frequently in controls in comparison to patients with hepatitis B virus and hepatocellular carcinoma (P = 0.0002 and P<0.0001) conferring a protective effect. Ficolin-2 levels differed significantly between patients and controls (p<0.0001). Patients with acute hepatitis B had higher serum Ficolin-2 levels compared to other patient groups and controls.The viral load was observed to be significantly distributed among the haplotypes (P = 0.04) and the AAAG haplotype contributed to higher Ficolin-2 levels and to viral load. Four novel single nucleotide polymorphisms in introns (-941G>T, -310G>A, +2363G>A, +4882G>A) and one synonymous mutation in exon 8 (+6485G>T) was observed. Strong linkage was found between the variant -986G>A and -4A>G. The very first study on Vietnamese cohort associates both Ficolin-2 serum levels and FCN2 haplotypes to hepatitis B virus infection and subsequent disease progression.     

Association between the C.1161G>A and C.1779C>G Genetic Variants of XRCC1 Gene and Hepatocellular Carcinoma Risk in Chinese Population

The human X-ray repair complementing group 1 gene (XRCC1) is an important candidate gene influencing hepatocellular carcinoma (HCC) susceptibility. The objective of this study was to detect the association between c.1161G>A and c.1779C>G variants of XRCC1 gene and HCC risk. This study was conducted in Chinese population consisting of 623 HCC cases and 639 controls. These two genetic variants could be genotyped by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. The association of XRCC1 gene variants with the risk of HCC was investigated under different genetic models. Our findings suggested that the genotypes/alleles from c.1161G>A and c.1779C>G genetic variants were statistically associated with HCC risk. As for the c.1161G>A, the AA genotype was statistically associated with the increased risk of HCC compared to GG wild genotype (OR = 2.36, 95% CI 1.63-3.40, P < 0.001). As for the c.1779C>G, the risk of HCC was significantly higher for GG genotype compared to CC wild genotype (OR = 2.17, 95% CI 1.51-3.12, P < 0.001). Furthermore, significant differences in the risk of HCC were also detected in other genetic models for these two variants. The allele-A of c.1161G>A and allele-G of c.1779C>G variants may contribute to the susceptibility of HCC (A versus G: OR = 1.48, 95% CI 1.26-1.75, P < 0.001 and G versus C: OR = 1.51, 95% CI 1.28-1.78, P < 0.001). Our data indicated that these two variants of XRCC1 gene were statistically associated with HCC risk in Chinese population.     

Mutations of the mitochondrial-tRNA modifier MTO1 cause hypertrophic cardiomyopathy and lactic acidosis

Dysfunction of mitochondrial respiration is an increasingly recognized cause of isolated hypertrophic cardiomyopathy. To gain insight into the genetic origin of this condition, we used next-generation exome sequencing to identify mutations in MTO1, which encodes mitochondrial translation optimization 1. Two affected siblings carried a maternal c.1858dup (p.Arg620Lysfs^∗8) frameshift and a paternal c.1282G>A (p.Ala428Thr) missense mutation. A third unrelated individual was homozygous for the latter change. In both humans and yeast, MTO1 increases the accuracy and efficiency of mtDNA translation by catalyzing the 5-carboxymethylaminomethylation of the wobble uridine base in three mitochondrial tRNAs (mt-tRNAs). Accordingly, mutant muscle and fibroblasts showed variably combined reduction in mtDNA-dependent respiratory chain activities. Reduced respiration in mutant cells was corrected by expressing a wild-type MTO1 cDNA. Conversely, defective respiration of a yeast mto1Δ strain failed to be corrected by an Mto1^Pro622∗ variant, equivalent to human MTO1^{Arg620Lysfs∗8}, whereas incomplete correction was achieved by an Mto1^Ala431Thr variant, corresponding to human MTO1^Ala428Thr. The respiratory yeast phenotype was dramatically worsened in stress conditions and in the presence of a paromomycin-resistant (P^R) mitochondrial rRNA mutation. Lastly, in vivo mtDNA translation was impaired in the mutant yeast strains.     

Arabidopsis VPS35, a retromer component, is required for vacuolar protein sorting and involved in plant growth and leaf senescence

The retromer complex is responsible for retrograde transport,which is coordinated with anterograde transport in the secretorypathway including vacuolar protein sorting. Yeast VPS35 is acomponent of the retromer complex that is essential for recognitionof specific cargo molecules. The physiological function of VPS35has not been determined in vacuolar protein sorting in higherorganisms. Arabidopsis thaliana has three VPS35 homologs designatedVPS35a, VPS35b and VPS35c. We isolated four vps35 mutants (vps35a-1,vps35b-1, vps35b-2 and vps35c-1) and then generated four doublemutants and one triple mutant. vps35a-1 vps35c-1 exhibited nounusual phenotypes. On the other hand, vps35b-1 vps35c-1 andthe triple mutant (vps35a-1 vps35b-2 vps35c-1) exhibited severephenotypes: dwarfism, early leaf senescence and fragmentationof protein storage vacuoles (PSVs). In addition, these mutantsmis-sorted storage proteins by secreting them out of the cellsand accumulated a higher level of vacuolar sorting receptor(VSR) than the wild type. VPS35 was localized in pre-vacuolarcompartments (PVCs), some of which contained VSR. VPS35 wasimmunoprecipitated with VPS29/MAG1, another component of theretromer complex. Our findings suggest that VPS35, mainly VPS35b,is involved in sorting proteins to PSVs in seeds, possibly byrecycling VSR from PVCs to the Golgi complex, and is also involvedin plant growth and senescence in vegetative organs.     

Mechanisms Governing the Endosomal Membrane Recruitment of the Core Retromer in Arabidopsis

The retromer complex localizes to endosomal membranes and is involved in protein trafficking. In mammals, it is composed of a dimer of sorting nexins and of the core retromer consisting of vacuolar protein sorting (VPS)26, VPS29, and VPS35. Although homologs of these proteins have been identified in plants, how the plant retromer functions remains elusive. To better understand the role of VPS components in the assembly and function of the core retromer, we characterize here Arabidopsis vps26-null mutants. We show that impaired VPS26 function has a dramatic effect on VPS35 levels and causes severe phenotypic defects similar to those observed in vps29-null mutants. This implies that functions of plant VPS26, VPS29, and VPS35 are tightly linked. Then, by combining live-cell imaging with immunochemical and genetic approaches, we report that VPS35 alone is able to bind to endosomal membranes and plays an essential role in VPS26 and VPS29 membrane recruitment. We also show that the Arabidopsis Rab7 homolog RABG3f participates in the recruitment of the core retromer to the endosomal membrane by interacting with VPS35. Altogether our data provide original information on the molecular interactions that mediate assembly of the core retromer in plants.     

Role of Ceramides and Sphingolipids in Parkinson's Disease

Sphingolipids, including the basic ceramide, are a subset of bioactive lipids that consist of many different species. Sphingolipids are indispensable for proper neuronal function, and an increasing number of studies have emerged on the complexity and importance of these lipids in (almost) all biological processes. These include regulation of mitochondrial function, autophagy, and endosomal trafficking, which are affected in Parkinson’s disease (PD). PD is the second most common neurodegenerative disorder and is characterized by the loss of dopaminergic neurons. Currently, PD cannot be cured due to the lack of knowledge of the exact pathogenesis. Nonetheless, important advances have identified molecular changes in mitochondrial function, autophagy, and endosomal function. Furthermore, recent studies have identified ceramide alterations in patients suffering from PD, and in PD models, suggesting a critical interaction between sphingolipids and related cellular processes in PD. For instance, autosomal recessive forms of PD cause mitochondrial dysfunction, including energy production or mitochondrial clearance, that is directly influenced by manipulating sphingolipids. Additionally, endo-lysosomal recycling is affected by genes that cause autosomal dominant forms of the disease, such as VPS35 and SNCA. Furthermore, endo-lysosomal recycling is crucial for transporting sphingolipids to different cellular compartments where they will execute their functions.This review will discuss mitochondrial dysfunction, defects in autophagy, and abnormal endosomal activity in PD and the role sphingolipids play in these vital molecular processes.     

VPS35 D620N knockin mice recapitulate cardinal features of Parkinson’s disease

D620N mutation in the vacuolar protein sorting 35 ortholog (VPS35) gene causes late‐onset, autosomal dominant familial Parkinson''s disease (PD) and contributes to idiopathic PD. However, how D620N mutation leads to PD‐related deficits in vivo remains unclear. In the present study, we thoroughly characterized the biochemical, pathological, and behavioral changes of a VPS35 D620N knockin (KI) mouse model with chronic aging. We reported that this VPS35 D620N KI model recapitulated a spectrum of cardinal features of PD at 14 months of age which included age‐dependent progressive motor deficits, significant changes in the levels of dopamine (DA) and DA metabolites in the striatum, and robust neurodegeneration of the DA neurons in the SNpc and DA terminals in the striatum, accompanied by increased neuroinflammation, and accumulation and aggregation of α‐synuclein in DA neurons. Mechanistically, D620N mutation induced mitochondrial fragmentation and dysfunction in aged mice likely through enhanced VPS35‐DLP1 interaction and increased turnover of mitochondrial DLP1 complexes in vivo. Finally, the VPS35 D620N KI mice displayed greater susceptibility to MPTP‐mediated degeneration of nigrostriatal pathway, indicating that VPS35 D620N mutation increased vulnerability of DA neurons to environmental toxins. Overall, this VPS35 D620N KI mouse model provides a powerful tool for future disease modeling and pharmacological studies of PD. Our data support the involvement of VPS35 in the development of α‐synuclein pathology in vivo and revealed the important role of mitochondrial fragmentation/dysfunction in the pathogenesis of VPS35 D620N mutation‐associated PD in vivo.     

Association between genetic variants in DNA and histone methylation and telomere length

Telomere length, a biomarker of aging and age-related diseases, exhibits wide variation between individuals. Common genetic variation may explain some of the individual differences in telomere length. To date, however, only a few genetic variants have been identified in the previous genome-wide association studies. As emerging data suggest epigenetic regulation of telomere length, we investigated 72 single nucleotide polymorphisms (SNPs) in 46 genes that involve DNA and histone methylation as well as telomerase and telomere-binding proteins and DNA damage response. Genotyping and quantification of telomere length were performed in blood samples from 989 non-Hispanic white participants of the Sister Study, a prospective cohort of women aged 35–74 years. The association of each SNP with logarithmically-transformed relative telomere length was estimated using multivariate linear regression. Six SNPs were associated with relative telomere length in blood cells with p-values<0.05 (uncorrected for multiple comparisons). The minor alleles of BHMT rs3733890 G>A (p = 0.041), MTRR rs2966952 C>T (p = 0.002) and EHMT2 rs558702 G>A (p = 0.008) were associated with shorter telomeres, while minor alleles of ATM rs1801516 G>A (p = 0.031), MTR rs1805087 A>G (p = 0.038) and PRMT8 rs12299470 G>A (p = 0.019) were associated with longer telomeres. Five of these SNPs are located in genes coding for proteins involved in DNA and histone methylation. Our results are consistent with recent findings that chromatin structure is epigenetically regulated and may influence the genomic integrity of telomeric region and telomere length maintenance. Larger studies with greater coverage of the genes implicated in DNA methylation and histone modifications are warranted to replicate these findings.     

The essential role of centrosomal NDE1 in human cerebral cortex neurogenesis

We investigated three families whose offspring had extreme microcephaly at birth and profound mental retardation. Brain scans and postmortem data showed that affected individuals had brains less than 10% of expected size (≤10 standard deviation) and that in addition to a massive reduction in neuron production they displayed partially deficient cortical lamination (microlissencephaly). Other body systems were apparently unaffected and overall growth was normal. We found two distinct homozygous mutations of NDE1, c.83+1G>T (p.Ala29GlnfsX114) in a Turkish family and c.684_685del (p.Pro229TrpfsX85) in two families of Pakistani origin. Using patient cells, we found that c.83+1G>T led to the use of a novel splice site and to a frameshift after NDE1 exon 2. Transfection of tagged NDE1 constructs showed that the c.684_685del mutation resulted in a NDE1 that was unable to localize to the centrosome. By staining a patient-derived cell line that carried the c.83+1G>T mutation, we found that this endogeneously expressed mutated protein equally failed to localize to the centrosome. By examining human and mouse embryonic brains, we determined that NDE1 is highly expressed in neuroepithelial cells of the developing cerebral cortex, particularly at the centrosome. We show that NDE1 accumulates on the mitotic spindle of apical neural precursors in early neurogenesis. Thus, NDE1 deficiency causes both a severe failure of neurogenesis and a deficiency in cortical lamination. Our data further highlight the importance of the centrosome in multiple aspects of neurodevelopment.     

Variants of OTOF and PJVK genes in Chinese patients with auditory neuropathy spectrum disorder

Background

Mutations in OTOF and PJVK genes cause DFNB9 and DFNB59 types of hearing loss, respectively. The patients carrying pathogenic mutations in either of these genes may show the typical phenotype of auditory neuropathy spectrum disorder (ANSD). The aim of the present study was to identify OTOF and PJVK mutations in sporadic ANSD patients.

Methods and Findings

A total of 76 unrelated Chinese non-syndromic ANSD patients were sequenced on the gene OTOF and PJVK exon by exon. Variants were valued in 105 controls with normal hearing to verify the carrying rate. We identified one pathogenic mutation (c.1194T>A) and three novel, possibly pathogenic, variants (c.3570+2T>C, c.4023+1 G>A, and c.1102G>A) in the OTOF gene, and one novel, possibly pathogenic, variant (c.548G>A) in PJVK. Moreover, we found three novel missense mutations within the exons of OTOF.

Conclusions

As we identified 4 and 1 possible pathogenic variants of the OTOF gene and the PJVK gene, respectively, we believe that screening in these genes are important in sporadic ANSD patients. The pathogenicity of these novel mutations needs further study because of their single heterozygous nature. Knowledge on the mutation spectra of these genes in Chinese would be beneficial in understanding the genetic character of this worldwide disease.     

A Missense Mutation in KCTD17 Causes Autosomal Dominant Myoclonus-Dystonia

Myoclonus-dystonia (M-D) is a rare movement disorder characterized by a combination of non-epileptic myoclonic jerks and dystonia. SGCE mutations represent a major cause for familial M-D being responsible for 30%–50% of cases. After excluding SGCE mutations, we identified through a combination of linkage analysis and whole-exome sequencing KCTD17 c.434 G>A p.(Arg145His) as the only segregating variant in a dominant British pedigree with seven subjects affected by M-D. A subsequent screening in a cohort of M-D cases without mutations in SGCE revealed the same KCTD17 variant in a German family. The clinical presentation of the KCTD17-mutated cases was distinct from the phenotype usually observed in M-D due to SGCE mutations. All cases initially presented with mild myoclonus affecting the upper limbs. Dystonia showed a progressive course, with increasing severity of symptoms and spreading from the cranio-cervical region to other sites. KCTD17 is abundantly expressed in all brain regions with the highest expression in the putamen. Weighted gene co-expression network analysis, based on mRNA expression profile of brain samples from neuropathologically healthy individuals, showed that KCTD17 is part of a putamen gene network, which is significantly enriched for dystonia genes. Functional annotation of the network showed an over-representation of genes involved in post-synaptic dopaminergic transmission. Functional studies in mutation bearing fibroblasts demonstrated abnormalities in endoplasmic reticulum-dependent calcium signaling. In conclusion, we demonstrate that the KCTD17 c.434 G>A p.(Arg145His) mutation causes autosomal dominant M-D. Further functional studies are warranted to further characterize the nature of KCTD17 contribution to the molecular pathogenesis of M-D.