Biomedical subjects
Publications and source records attributed to Andrew Singleton.
We describe a patient with juvenile levodopa-responsive Parkinsonism who reported a dramatic response to cigarette smoking with transient but marked improvement of motor symptoms associated with oculogyric crises and psychotic behavior. His beta-CIT single-photon emission computed tomography scan showed a complete absence of presynaptic dopaminergic nerve terminals.
BACKGROUND: A new locus for amyotrophic lateral sclerosis--frontotemporal dementia (ALS-FTD) has recently been ascribed to chromosome 9p. METHODS: We identified chromosome 9p segregating haplotypes within two families with ALS-FTD (F476 and F2) and undertook mutational screening of candidate genes within this locus. RESULTS: Candidate gene sequencing at this locus revealed the presence of a disease segregating stop mutation (Q342X) in the intraflagellar transport 74 (IFT74) gene in family 476 (F476), but no mutation was detected within IFT74 in family 2 (F2). While neither family was sufficiently informative to definitively implicate or exclude IFT74 mutations as a cause of chromosome 9-linked ALS-FTD, the nature of the mutation observed within F476 (predicted to truncate the protein by 258 amino acids) led us to sequence the open reading frame of this gene in a large number of ALS and FTD cases (n = 420). An additional sequence variant (G58D) was found in a case of sporadic semantic dementia. I55L sequence variants were found in three other unrelated affected individuals, but this was also found in a single individual among 800 Human Diversity Gene Panel samples. CONCLUSION: Confirmation of the pathogenicity of IFT74 sequence variants will require screening of other chromosome 9p-linked families.
The recent hapmap effort has placed focus on the application of genome-wide SNP analysis to assess the contribution of genetic variability, particularly SNPs, to traits such as disease. Here, we describe the utility of genome-wide SNP analysis in the direct detection of extended homozygosity and structural genomic variation. We use this approach to assess the frequency of genomic alterations resulting from the lymphoblast immortalization and culture processes commonly used in cell repositories. We have assayed 408 804 SNPs in 276 DNA samples extracted from Epstein-Barr virus immortalized cell lines, which were derived from lymphocytes of elderly neurologically normal subjects. These data reveal extended homozygosity (contiguous tracts >5 Mb) in 9.5% (26/272) and 340 structural genomic alterations in 182 (66.9%) DNA samples assessed, 66% of which did not overlap with previously described structural variations. Examination of DNA extracted directly from the blood of 30 of these subjects confirmed all examined instances of extended homozygosity (6/6), 75% of structural genomic alteration <5 Mb in size (12/16) and 13% (1/8) of structural genomic alteration >5 Mb in size. These data suggest that structural genomic variation is a common phenomenon in the general population. While a proportion of this variability may be caused or its relative abundance altered by the immortalization and clonal process this will have only a minor effect on genotype and allele frequencies in a large cohort. It is likely that this powerful methodology will augment existing techniques in the identification of chromosomal abnormalities.
The International HapMap Project and the arrival of technologies that type more than 100,000 SNPs in a single experiment have made genome-wide single nucleotide polymorphism (GW-SNP) assay a realistic endeavor. This has sparked considerable debate regarding the promise of GW-SNP typing to identify genetic association in disease. As has already been shown, this approach has the potential to localize common genetic variation underlying disease risk. The data provided from this technology also lends itself to several other lines of investigation; autozygosity mapping in consanguineous families and outbred populations, direct detection of structural variation, admixture analysis, and other population genetic approaches. In this review we will discuss the potential uses and practical application of GW-SNP typing including those above and beyond simple association testing.
BACKGROUND: Pathological brain iron deposition has been implicated as a source of neurotoxic reactive oxygen species in Alzheimer (AD) and Parkinson diseases (PD). Iron metabolism is associated with the gene hemochromatosis (HFE Human genome nomenclature committee ID:4886), and mutations in HFE are a cause of the iron mismetabolism disease, hemochromatosis. Several reports have tested the association of HFE variants with neurodegenerative diseases, such as AD and PD with conflicting results. METHODS: Genotypes were analysed for the two most common variants of HFE in a series of 130 AD, 55 Mild Cognitive Impairment (MCI) and 132 PD patients. Additionally, a series of 115 healthy age-matched controls was also screened. RESULTS: A statistically significant association was found in the PD group when compared to controls, showing that the presence of the C282Y variant allele may confer higher risk for developing the disease. CONCLUSION: Taken together these results suggest that the common variants in HFE may be a risk factor for PD, but not for AD in the Portuguese population.
Mutations in the LRRK2 gene, coding for dardarin, cause dominantly inherited Parkinson's disease (PD). Dardarin is a large protein, and mutations are found throughout the gene including the kinase domain. However, it is not clear if kinase activity is important for the damaging effects of pathogenic mutations. In this study, we noted two cellular phenotypes associated with mutant dardarin. First, pathogenic mutations increase the tendency of dardarin to form inclusion bodies. Secondly, neurons and neuronal cell lines undergo cell death after expression of mutant protein. Manipulating activity by replacing the kinase domain with a 'kinase-dead' version blocks inclusion body formation and strongly delays cell death. This predicts that kinase inhibitors will be useful therapeutic agents in patients with LRRK2 mutations and, perhaps, in sporadic PD. We also show that dardarin protein is expressed within human midbrain neurons and that C-terminal epitopes are also found in some Lewy bodies.
Using the well-characterized, human diversity sample series, we show that the V129 prion allele has a very high frequency in South American populations relative to the East Asian populations from which it arose. We suggest there has been selection at the prion locus, possibly mediated by Kuru-like diseases, which has influenced its allele frequency.
Until 10 years ago, conventional wisdom held that Parkinson's disease was not a genetic disorder. Since that time, there have been a plethora of genetic findings, culminating in the cloning of several genes that derive from the loci given the nomenclature PARK1-PARK12 (OMIM 168600). Recently, these research findings have begun to impact clinical practice, and this impact is likely to increase. The primary purpose of this article is to outline these genetic advances, discuss their importance for current practice in clinical and related settings, and outline briefly how they are influencing research into the causes of and possible future treatments for this prevalent disorder.
The alpha-synuclein Rep1 polymorphism was studied in patients and controls in an ethnic Greek population. There was an association of allele 2 with risk of Parkinson's disease (PD; adjusted odd ratio = 3.25; 95% CI = 1.80-5.87). Survival analyses (Cox proportional hazards models) were employed to explore the influence of genotypes on age at onset of PD. Age at onset of carriers of at least one Rep1 allele 2 was earlier (3.6 years) compared to noncarriers (adjusted hazard ratio = 2.21; 95% CI = 1.58-3.10). Kaplan-Meier analysis also supported a dosage effect of Rep1 allele 2 on age at onset. For Rep1 allele 1, there was neither association with risk of PD nor influence on age at onset. This is the first study showing an influence of Rep1 polymorphism on age at onset of PD.
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Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene have been shown to cause autosomal dominant and sporadic Parkinson's disease (PD). We report here the frequency of a common heterozygous mutation, 2877510G>A, which produces a glycine-to-serine amino acid substitution at codon 2019 in idiopathic Taiwanese PD. The extreme rarity of the G2019S mutation in our population suggests the occurrence of this mutation resulted from a common European founder.
BACKGROUND: Several genes underlying rare monogenic forms of Parkinson's disease have been identified over the past decade. Despite evidence for a role for genetics in sporadic Parkinson's disease, few common genetic variants have been unequivocally linked to this disorder. We sought to identify any common genetic variability exerting a large effect in risk for Parkinson's disease in a population cohort and to produce publicly available genome-wide genotype data that can be openly mined by interested researchers and readily augmented by genotyping of additional repository subjects. METHODS: We did genome-wide, single-nucleotide-polymorphism (SNP) genotyping of publicly available samples from a cohort of Parkinson's disease patients (n=267) and neurologically normal controls (n=270). More than 408,000 unique SNPs were used from the Illumina Infinium I and HumanHap300 assays. FINDINGS: We have produced around 220 million genotypes in 537 participants. This raw genotype data has been and as such is the first publicly accessible high-density SNP data outside of the International HapMap Project. We also provide here the results of genotype and allele association tests. INTERPRETATION: We generated publicly available genotype data for Parkinson's disease patients and controls so that these data can be mined and augmented by other researchers to identify common genetic variability that results in minor and moderate risk for disease.
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Mutations in the leucine-rich kinase 2 gene (LRRK 2) encoding dardarin, on chromosome 12, are a common cause of familial and sporadic Parkinson's disease. The most common mutation, a heterozygous 6055 G>A transition (G 2019 S) accounts for approximately 3--10% of familial Parkinson's disease and 1--8% sporadic Parkinson's disease in several European-derived populations. Some families with disease caused by LRRK 2 mutations have been reported to include patients with highly variable clinical and pathological features. We screened for the most common LRRK 2 mutation in a series of patients with Parkinson's Disease, Alzheimer's disease, Progressive Supranuclear Palsy, Multiple System Atrophy and frontotemporal dementia, as well as in neurologically normal controls. The mutation was found only in Parkinson's disease patients or their relatives and not in those with other neurodegenerative disease.
Analysis of the apolipoprotein E genotype in sibpairs with Parkinson's disease showed the E4 allele was over represented in those who shared the adjacent chromosome 19 markers. This suggests that apolipoprotein E4 is responsible for the linkage peak in this region and that it is a modest risk factor for Parkinson's disease.
Autosomal recessive juvenile parkinsonism (AR-JP, PARK2) is characterized by an early onset parkinsonism, often presenting with dystonia as an early feature. Mutations in Parkin are a relatively common cause of AR-JP and are estimated to be present in approximately 30% of familial young onset Parkinson disease (PD) [Abbas et al. (1999); Hum Mol Genet 8:567-574]. These mutations include exon rearrangements (deletions and duplications), point mutations, and small deletions. Similar genomic mutations have been described in unrelated patients, thereby indicating independent mutational events or ancient founder effects. We have identified homozygous deletion mutations of exon 4 in Parkin in two unrelated families, one from Brazil and the other from Turkey [Dogu et al. (2004); Mov Dis 9:812-816; Khan et al., Mov Dis, in press]. We have performed molecular analysis of the deletion breakpoints and this data indicates these mutations originated independently. We present here data demonstrating that the mutation responsible for disease in the Brazilian kindred consists of two separate deletions (1,069 and 1,750 bp) surrounding and including exon 4. The deletion removing parkin exon 4 identified in the Turkish family extended 156,203 bp. In addition to demonstrating that disease in these families is not caused by a single founder mutation, these data show that there is no common fragile site between these mutational events.
BACKGROUND: Alcohol dehydrogenases (ADHs) may be involved in the pathogenesis of neurodegenerative disorders because of their multiple roles in detoxification pathways and retinoic acid synthesis. In a previous study, significant association of an ADH class IV allele with Parkinson disease (PD) was found in a Swedish sample. PATIENTS: The previously associated single-nucleotide polymorphism plus 12 further polymorphisms in the ADH cluster on human chromosome 4q23 were screened for association in an extension of the original sample that now included 123 Swedish PD patients and 127 geographically matched control subjects. A rare nonsense single-nucleotide polymorphism in ADH1C (G78stop, rs283413) was identified in 3 of these patients but in no controls. To obtain sufficient power to detect a possible association of this rare variant with disease, we screened a large international sample of 1076 PD patients of European ancestry and 940 matched controls. RESULTS: The previously identified association with an ADH class IV allele remained significant (P<.02) in the extended Swedish study. Furthermore, in the international collaboration, the G78stop mutation in ADH1C was found in 22 (2.0%) of the PD patients but only in 6 controls (0.6%). This association was statistically significant (chi(2)(1) = 7.5; 2-sided P = .007; odds ratio, 3.25 [95% confidence interval, 1.31-8.05]). In addition, the G78stop mutation was identified in 4 (10.0%) of 40 Caucasian index cases with PD with mainly hereditary forms of the disorder. CONCLUSION: Findings presented herein provide further evidence for mutations in genes encoding ADHs as genetic risk factors for PD.
Previous work has suggested that in many neurological diseases genetic variability in the loci predisposing subjects to autosomal dominant disease contributes to the risk of sporadic disease. Here, using a population-based sample of dystonia cases, we show an association with the torsin A haplotype and sporadic idiopathic dystonia.