Oswaldo Lorenzo-Betancor

Rare coding variants in the phospholipase D3 gene confer risk for Alzheimer's disease

Genome-wide association studies (GWAS) have identified several risk variants for late-onset Alzheimers disease (LOAD). These common variants have replicable but small effects on LOAD risk and generally do not have obvious functional effects. Low-frequency coding variants, not detected by GWAS, are predicted to include functional variants with larger effects on risk. To identify low-frequency coding variants with large effects on LOAD risk, we carried out whole-exome sequencing (WES) in 14 large LOAD families and follow-up analyses of the candidate variants in several large LOAD case–control data sets. A rare variant in PLD3 (phospholipase D3; Val232Met) segregated with disease status in two independent families and doubled risk for Alzheimer’s disease in seven independent case–control series with a total of more than 11,000 cases and controls of European descent. Gene-based burden analyses in 4,387 cases and controls of European descent and 302 African American cases and controls, with complete sequence data for PLD3, reveal that several variants in this gene increase risk for Alzheimer’s disease in both populations. PLD3 is highly expressed in brain regions that are vulnerable to Alzheimer’s disease pathology, including hippocampus and cortex, and is expressed at significantly lower levels in neurons from Alzheimer’s disease brains compared to control brains. Overexpression of PLD3 leads to a significant decrease in intracellular amyloid-β precursor protein (APP) and extracellular Aβ42 and Aβ40 (the 42- and 40-residue isoforms of the amyloid-β peptide), and knockdown of PLD3 leads to a significant increase in extracellular Aβ42 and Aβ40. Together, our genetic and functional data indicate that carriers of PLD3 coding variants have a twofold increased risk for LOAD and that PLD3 influences APP processing. This study provides an example of how densely affected families may help to identify rare variants with large effects on risk for disease or other complex traits.

Replication of MAPT and SNCA, but not PARK16-18, as susceptibility genes for Parkinson's disease.

Recent genome‐wide association studies of Parkinsons disease have nominated 3 new susceptibility loci (PARK16‐18) and confirmed 2 known risk genes (MAPT and SNCA) in populations of European ancestry. We sought to replicate these findings. We genotyped single‐nucleotide polymorphisms in each of these genes/loci in 1445 Parkinsons disease patients and 1161 controls from northern Spain. Logistic regression was used to test for association between genotype and Parkinsons disease under an additive model, adjusting for sex, age, and site. We also performed analyses stratified by age at onset. Single‐nucleotide polymorphisms in MAPT (rs1800547; P = 3.1 × 10−4) and SNCA (rs356219; P = 5.5 × 10−4) were significantly associated with Parkinsons disease. However, none of the markers in PARK16‐18 associated with Parkinsons disease in the overall sample, or in any age stratum, with P values ranging from .09 to .88. Although our data further validate MAPT and SNCA as Parkinsons disease susceptibility genes, we failed to replicate PARK16, PARK17, and PARK18. Potential reasons for the discordance between our study and previous genome‐wide association studies include effects of population structure, power, and population‐specific environmental interactions. Our findings suggest that additional studies of PARK16‐18 are necessary to establish the role of these loci in modifying risk for Parkinsons disease in European‐derived populations.

Automated neuromelanin imaging as a diagnostic biomarker for Parkinson's disease.

We aimed to analyze the diagnostic accuracy of an automated segmentation and quantification method of the SNc and locus coeruleus (LC) volumes based on neuromelanin (NM)‐sensitive MRI (NM‐MRI) in patients with idiopathic (iPD) and monogenic (iPD) Parkinsons disease (PD).

Analysis of COQ2

BackgroundLoss of function COQ2 mutations results in primary CoQ10 deficiency. Recently, recessive mutations of the COQ2 gene have been identified in two unrelated Japanese families with multiple system atrophy (MSA). It has also been proposed that specific heterozygous variants in the COQ2 gene may confer susceptibility to sporadic MSA. To assess the frequency of COQ2 variants in patients with MSA, we sequenced the entire coding region and investigated all exonic copy number variants of the COQ2 gene in 97 pathologically-confirmed and 58 clinically-diagnosed MSA patients from the United States.ResultsWe did not find any homozygous or compound heterozygous pathogenic COQ2 mutations including deletion or multiplication within our series of MSA patients. In two patients, we identified two heterozygous COQ2 variants (p.S54W and c.403 + 10G > T) of unknown significance, which were not observed in 360 control subjects. We also identified one heterozygous carrier of a known loss of function p.S146N substitution in a severe MSA-C pathologically-confirmed patient.ConclusionsThe COQ2 p.S146N substitution has been previously reported as a pathogenic mutation in primary CoQ10 deficiency (including infantile multisystem disorder) in a recessive manner. This variant is the third primary CoQ10 deficiency mutation observed in an MSA case (p.R387X and p.R197H). Therefore it is possible that in the heterozygous state it may increase susceptibility to MSA. Further studies, including reassessing family history in patients of primary CoQ10 deficiency for the possible occurrence of MSA, are now warranted to resolve the role of COQ2 variation in MSA.

(Patho‐)physiological relevance of PINK1‐dependent ubiquitin phosphorylation

Mutations in PINK1 and PARKIN cause recessive, early‐onset Parkinsons disease (PD). Together, these two proteins orchestrate a protective mitophagic response that ensures the safe disposal of damaged mitochondria. The kinase PINK1 phosphorylates ubiquitin (Ub) at the conserved residue S65, in addition to modifying the E3 ubiquitin ligase Parkin. The structural and functional consequences of Ub phosphorylation (pS65‐Ub) have already been suggested from in vitro experiments, but its (patho‐)physiological significance remains unknown. We have generated novel antibodies and assessed pS65‐Ub signals in vitro and in cells, including primary neurons, under endogenous conditions. pS65‐Ub is dependent on PINK1 kinase activity as confirmed in patient fibroblasts and postmortem brain samples harboring pathogenic mutations. We show that pS65‐Ub is reversible and barely detectable under basal conditions, but rapidly induced upon mitochondrial stress in cells and amplified in the presence of functional Parkin. pS65‐Ub accumulates in human brain during aging and disease in the form of cytoplasmic granules that partially overlap with mitochondrial, lysosomal, and total Ub markers. Additional studies are now warranted to further elucidate pS65‐Ub functions and fully explore its potential for biomarker or therapeutic development.

Mitochondrial targeting sequence variants of the CHCHD2 gene are a risk for Lewy body disorders

Objective: To assess the role of CHCHD2 variants in patients with Parkinson disease (PD) and Lewy body disease (LBD) in Caucasian populations. Methods: All exons of the CHCHD2 gene were sequenced in a US Caucasian patient-control series (878 PD, 610 LBD, and 717 controls). Subsequently, exons 1 and 2 were sequenced in an Irish series (355 PD and 365 controls) and a Polish series (394 PD and 350 controls). Immunohistochemistry and immunofluorescence studies were performed on pathologic LBD cases with rare CHCHD2 variants. Results: We identified 9 rare exonic variants of unknown significance. These variants were more frequent in the combined group of PD and LBD patients compared to controls (0.6% vs 0.1%, p = 0.013). In addition, the presence of any rare variant was more common in patients with LBD (2.5% vs 1.0%, p = 0.050) compared to controls. Eight of these 9 variants were located within the genes mitochondrial targeting sequence. Conclusions: Although the role of variants of the CHCHD2 gene in PD and LBD remains to be further elucidated, the rare variants in the mitochondrial targeting sequence may be a risk factor for Lewy body disorders, which may link CHCHD2 to other genetic forms of parkinsonism with mitochondrial dysfunction.

Update on genetics of essential tremor

Despite the research, few advances in the etiopathogenesis on essential tremor (ET) have been made to date. The high frequency of positive family history of ET and the observed high concordance rates in monozygotic compared with dizygotic twins support a major role of genetic factors in the development of ET. In addition, a possible role of environmental factors has been suggested in the etiology of ET (at least in non‐familial forms). Although several gene variants in the LINGO1 gene may increase the risk of ET, to date no causative mutated genes have been identified. In this review, we summarize the studies performed on families with tremor, twin studies, linkage studies, case–control association studies, and exome sequencing in familial ET.

A search for SNCA 3' UTR variants identified SNP rs356165 as a determinant of disease risk and onset age in Parkinson's disease.

Alpha-synuclein gene (SNCA) polymorphisms have been associated with the common sporadic form of Parkinson’s disease (PD). We searched for DNA variants at the SNCA 3′ UTR through single strand conformation analysis and direct sequencing in a cohort of Spanish PD patients and controls. We have genotyped the rs356165 SNCA 3′ UTR polymorphism in a total of 1,135 PD patients and 772 healthy controls from two Spanish cohorts (Asturias and Navarre). We identified six SNCA 3′ UTR variants. Single nucleotide polymorphism (SNP) rs356165 was significantly associated with PD risk in the Spanish cohort (p = 0.0001; odd ratio = 1.37, 95%CI = 1.19–1.58). This SNP was also significantly associated with early age at onset of PD. Our work highlights rs356165 as an important determinant of the risk of developing PD and early age at onset and encourages future research to identify a functional effect on SNCA expression.

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 and risk for essential tremor: Results of a meta-analysis of rs9652490 and rs11856808

BACKGROUND/OBJECTIVES Recently, a genome-wide association study revealed a significant statistical association between LINGO1 rs9652490 and rs11856808 polymorphisms and the risk of developing essential tremor (ET) in Icelandic people. Because the results of further association studies were controversial, we conducted a meta-analysis including all the studies published on the risk of ET related with these polymorphisms. METHODS The metaanalysis included 11 association studies between LINGO1 rs9652490 (3972 ET patients, 20,714 controls) and 7 association studies between LINGO1 rs11856808, and risk for ET (2076 ET patients, 18,792 controls), and was carried out by using the software Meta-Disc 1.1.1 (http://www.hrc.es/investigacion/metadisc.html; Unit of Clinical Statistics, Hospital Ramón y Cajal, Madrid, Spain). Heterogeneity between studies in terms of degree of association was tested using the Q-statistic. RESULTS Global diagnostic odds-ratios (ORs) and 95% confidence intervals (CI) for rs9652490 and rs11856808 of the total series were, respectively, 1.17 (1.00-1.36) (p=0.069) and 1.20 (1.05-1.36) (p=0.016). After excluding data on Icelandic people of the discovery series (that was responsible of a high degree of heterogeneity for rs9652490 polymorphism), the ORs and CI were 1.10 (0.97-1.26) (p=0.063) and 1.12 (0.99-1.27) (p=0.034). Global ORs and 95% CI for rs9652490 and rs11856808 of familial ET patients were, respectively, 1.27 (1.03-1.57) (p=0.014) and 1.21 (1.10-1.44) (p=0.031). CONCLUSIONS The results of the meta-analysis suggest a relationship between LINGO1 rs11856808 polymorphism and the risk for ET and for familial ET, while rs9652490 polymorphism was only related with the risk for familial ET.