Missense mutations in TENM4, a regulator of axon guidance and central myelination, cause essential tremor.

Essential tremor (ET) is a common movement disorder with an estimated prevalence of 5% of the population aged over 65 years. In spite of intensive efforts, the genetic architecture of ET remains unknown. We used a combination of whole-exome sequencing and targeted resequencing in three ET families. In vitro and in vivo experiments in oligodendrocyte precursor cells and zebrafish were performed to test our findings. Whole-exome sequencing revealed a missense mutation in TENM4 segregating in an autosomal-dominant fashion in an ET family. Subsequent targeted resequencing of TENM4 led to the discovery of two novel missense mutations. Not only did these two mutations segregate with ET in two additional families, but we also observed significant over transmission of pathogenic TENM4 alleles across the three families. Consistent with a dominant mode of inheritance, in vitro analysis in oligodendrocyte precursor cells showed that mutant proteins mislocalize. Finally, expression of human mRNA harboring any of three patient mutations in zebrafish embryos induced defects in axon guidance, confirming a dominant-negative mode of action for these mutations. Our genetic and functional data, which is corroborated by the existence of a Tenm4 knockout mouse displaying an ET phenotype, implicates TENM4 in ET. Together with previous studies of TENM4 in model organisms, our studies intimate that processes regulating myelination in the central nervous system and axon guidance might be significant contributors to the genetic burden of this disorder.

LINGO1 gene analysis in Parkinson's disease phenotypes.

BACKGROUND: Parkinson's disease (PD) and essential tremor (ET) may share some etiopathogenic factors. A genome-wide association study has shown that LINGO1 gene variants are associated with increased risk of ET. We hypothesized that LINGO1 variants could increase susceptibility to PD. METHODS: A large series of PD subjects and healthy controls were genotyped for rs9652490 and rs11856808 LINGO1 single nucleotide polymorphisms (SNPs). RESULTS: We found an increased frequency of the rs11856808(T/T) genotype in PD compared with controls (odds ratio = 1.46; corrected P value = 0.02). A recessive genetic model was the best fit for rs11856808 influence on PD (recessive gene action test: corrected P value = 0.01). Stratification analysis showed that rs11856808(T/T) genotype frequency was higher in the tremor-dominant PD and the classical PD (C-PD) subgroups (recessive gene action test for the C-PD subgroup: corrected P value = 0.004). DISCUSSION: Our results indicate that LINGO1 variants could increase risk of PD, specifically those presenting the non-rigid-akinetic phenotypes, which suggests that LINGO1 may have a role in the etiology of tremor in PD at least in the Spanish population.

Exome-wide rare variant analysis in familial essential tremor.

INTRODUCTION: Essential tremor (ET) is one of the most common movement disorders. Despite its high prevalence and heritability, its genetic etiology remains elusive with only a few susceptibility genes identified and poorly replicated. Our aim was to find novel candidate genes involved in ET predisposition through whole exome sequencing. METHODS: We studied eight multigenerational families (N = 40 individuals) with an autosomal-dominant inheritance using a comprehensive strategy combining whole exome sequencing followed by case-control association testing of prioritized variants in a separate cohort comprising 521 ET cases and 596 controls. We further performed gene-based burden analyses in an additional dataset comprising 789 ET patients and 770 healthy individuals to investigate whether there was an enrichment of rare deleterious variants within our candidate genes. RESULTS: Fifteen variants co-segregated with disease status in at least one of the families, among which rs749875462 in CCDC183, rs535864157 in MMP10 and rs114285050 in GPR151 showed a nominal association with ET. However, we found no significant enrichment of rare variants within these genes in cases compared with controls. Interestingly, MMP10 protein is involved in the inflammatory response to neuronal damage and has been previously associated with other neurological disorders. CONCLUSIONS: We prioritized a set of promising genes, especially MMP10, for further genetic and functional studies in ET. Our study suggests that rare deleterious coding variants that markedly increase susceptibility to ET are likely to be found in many genes. Future studies are needed to replicate and further infer biological mechanisms and potential disease causality for our identified genes.

Rasagiline improves freezing in a patient with primary progressive freezing gait.

We herein report the case of a 84-year-old man with a 4-year history of freezing of gait (FOG) consistent with the diagnosis of primary progressive freezing gait. Single photon emission tomography (SPECT) with a radiolabeled ligand of the dopamine transporter (DAT-SPECT) showed integrity of striatal dopaminergic terminals, whereas brain perfusion SPECT disclosed multiple areas of decreased perfusion in frontal and parietal lobes, as well as in the subcortical gray nuclei of both sides. Treatment with the new irreversible monoamine oxidase B inhibitor rasagiline at standard doses resulted in a rapid, dramatic, and sustained improvement of the frequency and duration of FOG episodes. In addition, brain perfusion SPECT after treatment showed a marked increase of the activity in all cortical areas as well as in the basal ganglia and thalamus. Rasagiline may prove to be an effective and safe treatment for this disabling condition.

Pooled-DNA target sequencing of Parkinson genes reveals novel phenotypic associations in Spanish population.

Eighteen loci and several susceptibility genes have been related to Parkinson's disease (PD). However, most studies focus on single genes in small PD series. Our aim was to establish the genetic background of a large Spanish PD sample. Pooled-DNA target sequencing of 7 major PD genes (SNCA, PARK2, PINK1, DJ-1, LRRK2, GBA, and MAPT) was performed in 562 PD cases. Forty-four variants were found among 114 individuals (20.28%, p<0.05). Among these variants, 30 were found in Mendelian genes (68.18%) and 14 in PD susceptibility genes (31.82%). Seven novel variants were identified. Interestingly, most variants were found in PARK2 and PINK1 genes, whereas SNCA and DJ-1 variants were rare. Validated variants were also genotyped in Spanish healthy controls (n = 597). Carriers of heterozygous PARK2 variants presented earlier disease onset and showed dementia more frequently. PD subjects carrying 2 variants at different genes (1.42%) had an earlier age of onset and a predominantly akinetic-rigid PD phenotype (55.6%, p < 0.05), suggesting that the accumulation of genetic risk variants could modify PD phenotype.

Molecular genetics of a patient with Mohr-Tranebjaerg Syndrome due to a new mutation in the DDP1 gene.

The deafness-dystonia syndrome (DDS) or Mohr-Tranebjaerg syndrome (MTS, MIM 304700) is a rare X-linked recessive neurological disorder resulting from loss-of-function mutations in the nuclear DDP1/TIMM8A gene, involved in the transport and sorting of proteins to the mitochondrial inner membrane. A Mohr-Tranebjaerg patient and his mother were subjected to clinical and molecular studies. Screening of mutations were performed in TIMM8A, TIMM13, and other mitochondrial protein transport genes by conformation sensitive gel electrophoresis (CSGE), followed by direct DNA sequencing of tissue samples from the patient. Mitochondrial DNA of the patient was also sequenced at the genes for COX subunits and some mitochondrial tRNAs. Respiratory chain activities in a muscle biopsy and cultured fibroblasts from the patient were assessed using biochemical methods. mRNA expression of TIMM8A and TIMM13 was determined by RT-PCR in cultured fibroblasts. We identified a new case of Mohr-Tranebjaerg syndrome and report the characteristics of a new pathogenic de novo mutation (c.112C>T, pGln38X) in the TIMM8A gene. Biochemical measures of respiratory chain complex activities in muscle biopsy and fibroblasts did not show a major deficiency or alteration. mRNA expression studies demonstrated increased TIMM8A mRNA levels in cultured fibroblasts from the patient. Phenotypic differences among published cases seem not to be related with the mutation location or type. Our results support the idea that dysfunctions of mitochondrial protein transport, in addition to OXPHOS deficiency, can be the basis of important mitochondrial pathologies.

TREM2 R47H variant and risk of essential tremor: a cross-sectional international multicenter study.

INTRODUCTION: Essential tremor (ET) is the most frequent movement disorder in adults. Its pathophysiology is not clearly understood, however there is growing evidence showing common etiologic factors with other neurodegenerative disorders such as Alzheimer's and Parkinson's diseases (AD, PD). Recently, a rare p.R47H substitution (rs75932628) in the TREM2 protein (triggering receptor expressed on myeloid cells 2; OMIM: *605086) has been proposed as a risk factor for AD, PD and amyotrophic lateral sclerosis (ALS). The objective of the study was to determine whether TREM2 p.R47H allele is also a risk factor for developing ET. METHODS: This was a cross-sectional multicenter international study. An initial case-control cohort from Spain (n = 456 ET, n = 2715 controls) was genotyped. In a replication phase, a case-control series (n = 897 ET, n = 1449 controls) from different populations (Italy, Germany, North-America and Taiwan) was studied. Owed to the rarity of the variant, published results on p.R47H allele frequency from 14777 healthy controls from European, North American or Chinese descent were additionally considered. The main outcome measure was p.R47H (rs75932628) allelic frequency. RESULTS: There was a significant association between TREM2 p.R47H variant and ET in the Spanish cohort (odds ratio [OR], 5.97; 95% CI, 1.203-29.626; p = 0.042), but it was not replicated in other populations. CONCLUSIONS: These results argue in favor of population-specific differences in the allelic distribution and suggest that p.R47H (rs75932628) variant may contribute to the susceptibility of ET in Spanish population. However, taking into account the very low frequency of p.R47H, further confirmatory analyses of larger ET series are needed.

Polymorphism in genes involved in adrenergic signaling associated with Alzheimer's.

To investigate the potential involvement of adrenergic signaling in Alzheimer's disease (AD) pathogenesis, we performed genetic and functional studies of genes initiating the cascade. We chose two functional single-nucleotide polymorphisms (SNPs) in the beta1-adrenergic receptor (ADRB1) and the G protein beta3 subunit (GNB3) genes, respectively, and analyzed their allelic frequencies in a case-control sample of AD. We found that the GNB3 T allele produces a significant risk for AD in individuals homozygous for the ADRB1 C allele, suggesting that the combined effect of both polymorphisms influences AD susceptibility. Interestingly, the co-expression of GNB3 T and ADRB1 C alleles, compared with GNB3 C and ADRB1 G, produced increased cAMP levels and MAPK activation following adrenergic stimulation of transfected human cell lines. Furthermore, the co-expression of these alleles also produced increases in APP expression. These data strongly indicate that the combination of GNB3 and ADRB1 polymorphisms produces AD susceptibility by changing the cell responsiveness to adrenergic stimulation, pointing to the modulation of brain adrenergic receptors as a potential target for novel AD therapeutic strategies.

Nigrostriatal dopaminergic function in subjects with isolated action tremor.

BACKGROUND: Isolated action tremor (IAT) is the hallmark clinical feature of essential tremor (ET), but it may also be a prominent feature of some individuals with Parkinson's disease (PD) suggesting a pathogenic relationship between these two disorders. OBJECTIVES: We investigated the integrity of the striatal presynaptic dopaminergic system in subjects presenting IAT to improve the diagnostic accuracy and to explore any putative relationships between ET and PD. METHODS: The striatal dopaminergic system was examined by means of dopamine transporter imaging using (123)I-(fluoropropyl)-2ß-carbomethoxy-3ß-(4-iodophenyl) nortropane ([123I]-FP-CIT) single-photon emission tomography (DAT-SPECT) in a clinical series of individuals with IAT, excluding those with associated resting tremor and bradykinesia. RESULTS: Among 167 incidental individuals with IAT eligible for DAT-SPECT (Male/Female = 58.9/41.1%; Age = 67.8 ± 14.3 years), reduced striatal uptake was observed in 114 out of 167 (68.3%), whereas normal striatal binding was observed in the remaining 53 subjects (31.7%). Onset of tremor after 50 years and asymmetrical distribution of tremor were predictive variables of nigrostriatal denervation, whereas gender, family history and the presence of intentional, cephalic or voice tremors were not associated with nigrostriatal denervation. CONCLUSIONS: Our findings suggest that IAT is a frequent presenting symptom in a subset of individuals with PD, often misdiagnosed as ET, and that DAT-SPECT can help differentiate between these two disorders. Current diagnostic criteria for ET should be revised to include asymmetry and late-onset tremor as predictors of nigrostriatal denervation.

Genetic variation in APOE cluster region and Alzheimer's disease risk.

We report the fine mapping/sequencing results of promoter and regulatory regions of APOE cluster genes (APOE, APOC1, APOC4, APOC2, and TOMM40) in Alzheimer's disease (AD) risk as well as in the progression from mild cognitive impairment (MCI) to AD. Long-range sequencing in 29 MCI subjects who progressed to dementia revealed 7 novel variants. Two potentially relevant novel variants and 34 single nucleotide polymorphisms (SNPs) were genotyped in a large sample of AD, MCI, and control subjects (n = 1453). Globally, very little association signal was observed in our sample in the absence of APOE ε4. Rs5158 (APOC4 intron 1) and rs10413089 (3' to APOC2) showed a trend toward an increase in AD risk independently from APOE ε4 associated risk though it did not survive multiple test correction (uncorrected p = 0.0099 and 0.01, respectively). Interestingly, rs10413089 showed a similar effect in an independent series. The analysis of the discovery sample showed an association of TOMM40 single nucleotide polymorphisms with progression from MCI stage to AD (rs59007384 and rs11556510), as well as with a shorter time to progression from MCI status to AD (rs10119), though these results could not be replicated in independent series. Further studies are needed to investigate the role of APOE cluster variants in AD risk.

A TAP2 genotype associated with Alzheimer's disease in APOE4 carriers.

Sporadic Alzheimer's disease (AD) appears to be the consequence of the interaction between combinations of genes and environmental factors. Binding with the transporter associated with antigen processing (TAP) is thought to be the main way in which herpes simplex virus type 1 (HSV-1) evades immune surveillance. Several TAP gene polymorphisms were examined and a TAP2 SNP (rs241448) associated with AD found in two independent case-control samples, especially in carriers of the APOE4 allele. These findings are consistent with the hypothesis that human genetic variants facilitating the access of HSV-1 to the brain might result in susceptibility to AD.