Sofia A. Oliveira

Mutations in the pleckstrin homology domain of dynamin 2 cause dominant intermediate Charcot-Marie-Tooth disease

Charcot-Marie-Tooth (CMT) disease is a clinically and genetically heterogeneous group of peripheral neuropathies. Different chromosomal loci have been linked with three autosomal dominant, intermediate types of CMT: DI-CMTA, DI-CMTB and DI-CMTC. We refined the locus associated with DI-CMTB on chromosome 19p12–13.2 to 4.2 Mb in three unrelated families with CMT originating from Australia, Belgium and North America. After screening candidate genes, we identified unique mutations in dynamin 2 (DNM2) in all families. DNM2 belongs to the family of large GTPases and is part of the cellular fusion-fission apparatus. In transiently transfected cell lines, mutations of DNM2 substantially diminish binding of DNM2 to membranes by altering the conformation of the β3/β4 loop of the pleckstrin homology domain. Additionally, in the Australian and Belgian pedigrees, which carry two different mutations affecting the same amino acid, Lys558, CMT cosegregated with neutropenia, which has not previously been associated with CMT neuropathies.

Parkin mutations and susceptibility alleles in late-onset Parkinson's disease

Parkin, an E2‐dependent ubiquitin protein ligase, carries pathogenic mutations in patients with autosomal recessive juvenile parkinsonism, but its role in the late‐onset form of Parkinsons disease (PD) is not firmly established. Previously, we detected linkage of idiopathic PD to the region on chromosome 6 containing the Parkin gene (D6S305, logarithm of odds score, 5.47) in families with at least one subject with age at onset (AAO) younger than 40 years. Mutation analysis of the Parkin gene in the 174 multiplex families from the genomic screen and 133 additional PD families identified mutations in 18% of early‐onset and 2% of late‐onset families (5% of total families screened). The AAO of patients with Parkin mutations ranged from 12 to 71 years. Excluding exon 7 mutations, the mean AAO of patients with Parkin mutations was 31.5 years. However, mutations in exon 7, the first RING finger (Cys253Trp, Arg256Cys, Arg275Trp, and Asp280Asn) were observed primarily in heterozygous PD patients with a much later AAO (mean AAO, 49.2 years) but were not found in controls in this study or several previous reports (920 chromosomes). These findings suggest that mutations in Parkin contribute to the common form of PD and that heterozygous mutations, especially those lying in exon 7, act as susceptibility alleles for late‐onset form of Parkinson disease. Ann Neurol 2003

Revealing the role of glutathione S-transferase omega in age-at-onset of Alzheimer and Parkinson diseases

We previously reported a linkage region on chromosome 10q for age-at-onset (AAO) of Alzheimer (AD) and Parkinson (PD) diseases. Glutathione S-transferase, omega-1 (GSTO1) and the adjacent gene GSTO2, located in this linkage region, were then reported to associate with AAO of AD and PD. To examine whether GSTO1 and GSTO2 (hereafter referred to as GSTO1h) are responsible for the linkage evidence, we identified 39 families in AD that lead to our previous linkage and association findings. The evidence of linkage and association was markedly diminished after removing these 39 families from the analyses, thus providing support that GSTO1h drives the original linkage results. The maximum average AAO delayed by GSTO1h SNP 7-1 (rs4825, A nucleotide) was 6.8 (+/-4.41) years for AD and 8.6(+/-5.71) for PD, respectively. This is comparable to the magnitude of AAO difference by APOE-4 in these same AD and PD families. These findings suggest the presence of genetic heterogeneity for GSTO1hs effect on AAO, and support GSTO1hs role in modifying AAO in these two disorders.

Identification of Risk and Age-at-Onset Genes on Chromosome 1p in Parkinson Disease

We previously reported a linkage region on chromosome 1p (LOD = 3.41) for genes controlling age at onset (AAO) in Parkinson disease (PD). This region overlaps with the previously reported PARK10 locus. To identify the gene(s) associated with AAO and risk of PD in this region, we first applied a genomic convergence approach that combined gene expression and linkage data. No significant results were found. Second, we performed association mapping across a 19.2-Mb region centered under the AAO linkage peak. An iterative association mapping approach was done by initially genotyping single-nucleotide polymorphisms at an average distance of 100 kb apart and then by increasing the density of markers as needed. Using the overall data set of 267 multiplex families, we identified six associated genes in the region, but further screening of a subset of 83 families linked to the chromosome 1 locus identified only two genes significantly associated with AAO in PD: the gamma subunit of the translation initiation factor EIF2B gene (EIF2B3), which was more significant in the linked subset and the ubiquitin-specific protease 24 gene (USP24). Unexpectedly, the human immunodeficiency virus enhancer-binding protein 3 gene (HIVEP3) was found to be associated with risk for susceptibility to PD. We used several criteria to define significant results in the presence of multiple testing, including criteria derived from a novel cluster approach. The known or putative functions of these genes fit well with the current suspected pathogenic mechanisms of PD and thus show great potential as candidates for the PARK10 locus.

Association between the neuron-specific RNA-binding protein ELAVL4 and Parkinson disease

Inflammatory processes have been implicated in the cascade of events that lead to nerve cell death. In the nervous system, a number of genes involved in inflammation pathways are regulated post-transcriptionally via the interaction of their mRNAs with specific RNA-binding Hu proteins, the vertebrate homologues of the Drosophila ELAV (for embryonic lethal abnormal vision). The gene encoding ELAVL4, a member of the Hu family of proteins, is located 2xa0Mb from the chromosome 1p linkage region peak for age-at-onset (AAO) of Parkinson disease (PD) (LOD=3.41). Nine single-nucleotide polymorphisms (SNPs) in ELAVL4 were genotyped for 266 multiplex families (1,223 samples). Additional genotyping in 377 singleton families was performed for a subset of five SNPs (SNPs 1–5) that were not in linkage disequilibrium. SNP 2 (located in the first intron of ELAVL4) showed a strong significant association with AAO of PD (P=0.006), and SNP 5 (a coding SNP in ELAVL4) showed a moderately significant association (P=0.035). Haplotype analysis revealed that the A-C haplotype at SNPs 2 and 3 has the strongest significant association with AAO (P=0.0001) among all combinations of two or three loci. The A-C haplotype remained significant for AAO after the inclusion of the C allele at SNP 5 to this haplotype (A-C-C haplotype, P=0.00018). Although SNP 5 was found to associate with PD risk in the early-onset subset of PD families (at least one affected with AAO <40xa0years, 60 families), we believe that it is a by-product of its association with AAO. Taken together, these results suggest a potential role for ELAVL4 as a modifier gene for AAO of PD.

Linkage disequilibrium and haplotype tagging polymorphisms in the Tau H1 haplotype

Abstract.We and others have previously detected association of the Tau H1 haplotype on chromosome 17 with risk of idiopathic Parkinson disease (PD). The H1 haplotype appears to have a fundamental importance in neurodegeneration, as multiple studies have shown it is also associated with an increased risk for progressive supranuclear palsy, corticobasal degeneration, frontotemporal lobar degeneration syndromes, and primary progressive aphasia. Therefore, to divide the H1 haplotype into sub-haplotypes that could be more significantly associated with the risk of developing PD, and to delimit the genes lying in the H1 haplotype, we analyzed 34 single nucleotide polymorphisms (SNPs) spanning over 3.15 megabases in the region containing Tau. These SNPs are located in or flank the corticotropin-releasing hormone receptor 1, presenilin homolog 2, Tau,nSaitohin, and KIAA1267 genes. Analysis of linkage disequilibrium (LD) using these 34 SNPs suggests that the H1 haplotype extends over about 1.3 megabases, making it the largest region of LD reported to date. Of the 29 SNPs lying in this region of LD, 5 were identified as “haplotype tagging” SNPs (htSNPs), capturing 96% of the sample’s haplotype diversity. Association analysis with these htSNPs revealed a new H1 sub-haplotype that is significantly associated with PD (P<0.02). These results define the genes and regulatory regions included in this region of LD, containing an important susceptibility allele contributing to increased risk of neurodegeneration.

The Q7R Saitohin gene polymorphism is not associated with Alzheimer disease

Previous studies have reported conflicting results regarding the association of the Q7R polymorphism in the Saitohin gene with late-onset Alzheimer disease (AD). Given that AD is a tauopathy but no mutations or polymorphisms in Tau have been consistently associated with AD, and that Saitohin is nested in intron 9 of Tau and shares a similar expression pattern, we tested this association in 690 multiplex AD families and in a case-control sample (903 patients and 320 controls). We found no evidence of significant association of this polymorphism with risk of AD using family-based and case-control tests of association.

Dense genotyping of immune-related loci implicates host responses to microbial exposure in Behcet's disease susceptibility

We analyzed 1,900 Turkish Behçets disease cases and 1,779 controls genotyped with the Immunochip. The most significantly associated SNP was rs1050502, a tag SNP for HLA-B*51. In the Turkish discovery set, we identified three new risk loci, IL1A–IL1B, IRF8, and CEBPB–PTPN1, with genome-wide significance (P < 5 × 10−8) by direct genotyping and ADO–EGR2 by imputation. We replicated the ADO–EGR2, IRF8, and CEBPB–PTPN1 loci by genotyping 969 Iranian cases and 826 controls. Imputed data in 608 Japanese cases and 737 controls further replicated ADO–EGR2 and IRF8, and meta-analysis additionally identified RIPK2 and LACC1. The disease-associated allele of rs4402765, the lead marker at IL1A–IL1B, was associated with both decreased IL-1α and increased IL-1β production. ABO non-secretor genotypes for two ancestry-specific FUT2 SNPs showed strong disease association (P = 5.89 × 10−15). Our findings extend the list of susceptibility genes shared with Crohns disease and leprosy and implicate mucosal factors and the innate immune response to microbial exposure in Behçets disease susceptibility.

Dissecting A Complex Disease Using Modern Techniques of Molecular Biology

In the future, both clinical trials and laboratory tests are going to be heavily influenced by genetic susceptibility genes. These are genes whose polymorphic forms can increase a person’s risk of (but not necessarily cause) a common disease such as Alzheimer disease, cardiovascular disease or arthritis. We briefly describe the approach taken to identify these genes, using Parkinson disease (PD) as a model. PD is the second most common human neurodegenerative disorder and is commonly characterized by resting tremor, bradykinesia, and rigidity. The incidence and prevalence of PD increase with age, and thus, as the population ages, PD will increase. The main biochemical abnormality in PD seems to be the dopamine loss resulting from cell death in the substantia nigra region of the brain. However, no predictive test exists for PD. PD is thought to be a complex disease with either a polygenic (multiple genes) or multifactorial (genes and environment) etiology. Over the past few years debate has occurred whether PD has a genetic component or is just secondary to environmental influences. Here we discuss an approach we are following to evaluate the possible genetic component of PD. Haines and Pericak-Vance1 provide a good review of the complex genetic disease mapping process, and the steps are represented in the flowchart in F1.