Hyposmia in G2019S LRRK2-related parkinsonism: clinical and pathologic data.

BACKGROUND: Mutations in PARK8 (LRRK2) are associated with autosomal dominant parkinsonism and Parkinson disease (PD). Hyposmia is present in at least 80% of patients with PD and an accumulation of alpha-synuclein (alpha-syn) is seen in the olfactory pathways. In this study we have clinically examined olfaction and pathologically examined the rhinencephalon in individuals carrying the G2019S LRRK2 mutation. METHODS: The University of Pennsylvania Smell Test (UPSIT) was used to evaluate the sense of smell in 19 parkinsonian and two asymptomatic carriers of the G2019S mutation and compared with groups of patients with PD and healthy controls. Postmortem examination of alpha-syn accumulation in the rhinencephalon was also carried out in four parkinsonian carriers of the G2019S mutation. RESULTS: The mean UPSIT score in G2019S parkinsonian carriers was lower than that in healthy controls (p < 0.001) and similar to that found in patients with PD (p > 0.999). Smell tests in two asymptomatic carriers of the G2019S mutation were in the normal range. Postmortem studies of the olfactory pathways in one of the patients who had been clinically tested, and found to have hyposmia, and three other cases with the G2019S mutation, revealed alpha-syn deposition in the olfactory pathways in all cases. CONCLUSIONS: Odor identification is diminished in LRRK2 G2019S mutation parkinsonism but the asymptomatic carriers of the mutation had normal olfaction. We found alpha-syn accumulation with Lewy bodies in the rhinencephalon in all four cases examined pathologically.

Genetic association studies of complex neurological diseases.

Genetic association studies offer a powerful approach to identify the multiple variants of small effect that modulate susceptibility to common, complex disease. They, however, have a poor reputation, mainly because of the consistent lack of replication of all but a few. Thousands of genetic studies have been carried out on multifactorial diseases in the past 30 years, yielding only about 50 variants that can be considered to be true positives. Although the positive studies show proof of principle, the multitude of negative studies indicate fundamental problems in the design and execution of association studies. Here, we discuss some of the more pertinent study design and data analysis issues which can affect the outcome of genetic association studies.

PINK1 protein in normal human brain and Parkinson's disease.

Parkinson's disease is a common incurable neurodegenerative disease whose molecular aetiology remains unclear. The identification of Mendelian genes causing rare familial forms of Parkinson's disease has revealed novel proteins and pathways that are likely to be relevant in the pathogenesis of sporadic Parkinson's disease. Recently, mutations in a novel gene, PINK1, encoding a 581 amino acid protein with both mitochondrial targeting and serine/threonine kinase domains, were identified as a cause of autosomal recessive parkinsonism. This provided important evidence for the role of the mitochondrial dysfunction and kinase pathways in neurodegeneration. In this study, we report the first characterization of the PINK1 protein in normal human and sporadic Parkinson's brains, in addition to Parkinson's cases with heterozygous PINK1 mutations. The possible role of the PINK1 protein was also assessed in a number of neurodegenerative diseases characterized by proteinaceous inclusions. For these studies, rabbit polyclonal antibodies were raised against two peptide sequences within the N-terminal hydrophilic loops of PINK1 protein. Using immunohistochemistry and western blotting we were able to demonstrate that PINK1 is a ubiquitous protein expressed throughout the human brain and it is found in all cell types showing a punctate cytoplasmic staining pattern consistent with mitochondrial localization. Fractionation studies of human and rat brain confirm that PINK1 is localized to the mitochondrial membranes. In addition, we show that PINK1 is detected in a proportion of Lewy bodies in cases of sporadic Parkinson's disease and Parkinson's disease associated with heterozygous mutations in the PINK1 gene, which are clinically and pathologically indistinguishable from the sporadic cases. PINK1 was absent in cortical Lewy bodies, in neurofibrillary tangles in Alzheimer's disease, progressive supranuclear palsy and corticobasal degeneration, and in the glial and neuronal alpha-synuclein positive inclusions in multiple system atrophy. These studies provide for the first time in vivo morphological and biochemical evidence to support a mitochondrial localization of PINK1 and underpin the significance of mitochondrial dysfunction in the pathogenesis of nigral cell degeneration in Parkinson's disease.

The alpha-synuclein gene in multiple system atrophy.

BACKGROUND: The formation of alpha-synuclein aggregates may be a critical event in the pathogenesis of multiple system atrophy (MSA). However, the role of this gene in the aetiology of MSA is unknown and untested. METHOD: The linkage disequilibrium (LD) structure of the alpha-synuclein gene was established and LD patterns were used to identify a set of tagging single nucleotide polymorphisms (SNPs) that represent 95% of the haplotype diversity across the entire gene. The effect of polymorphisms on the pathological expression of MSA in pathologically confirmed cases was also evaluated. RESULTS AND CONCLUSION: In 253 Gilman probable or definite MSA patients, 457 possible, probable, and definite MSA cases and 1472 controls, a frequency difference for the individual tagging SNPs or tag-defined haplotypes was not detected. No effect was observed of polymorphisms on the pathological expression of MSA in pathologically confirmed cases.

Population genetic approaches to neurological disease: Parkinson's disease as an example.

Parkinson's disease (PD) is a common, progressive, incurable disabling condition. The cause is unknown but over the past few years tremendous progress in our understanding of the genetic bases of this condition has been made. To date, this has almost exclusively come from the study of relatively rare Mendelian forms of the disease and there are no currently, widely accepted common variants known to increase susceptibility. The role that the "Mendelian" genes play in common sporadic forms of PD is unknown. Moreover, most studies in PD can really be described as candidate polymorphism studies rather than true and complete assessments of the genes themselves. We provide a model of how one might tackle some of these issues using Parkinson's disease as an illustration. One of the emerging hypotheses of gene environment interaction in Parkinson's disease is based on drug metabolizing (or xenobiotic) enzymes and their interaction with putative environmental toxins. This motivated us to describe a tagging approach for an extensive but not exhaustive list of 55 drug metabolizing enzyme genes. We use these data to illustrate the power, and some of the limitations of a haplotype tagging approach. We show that haplotype tagging is extremely efficient and works well with only a modest increase in effort through different populations. The tagging approach works much less well if the minor allele frequency is below 5%. However, it will now be possible using these tags to evaluate these genes comprehensively in PD and other neurodegenerative conditions.

Linkage disequilibrium fine mapping and haplotype association analysis of the tau gene in progressive supranuclear palsy and corticobasal degeneration.

BACKGROUND: The haplotype H1 of the tau gene, MAPT, is highly associated with progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD). OBJECTIVE: To investigate the pathogenic basis of this association. METHODS: Detailed linkage disequilibrium and common haplotype structure of MAPT were examined in 27 CEPH trios using validated HapMap genotype data for 24 single nucleotide polymorphisms (SNPs) spanning MAPT. RESULTS: Multiple variants of the H1 haplotype were resolved, reflecting a far greater diversity of MAPT than can be explained by the H1 and H2 clades alone. Based on this, six haplotype tagging SNPs (htSNPs) that capture 95% of the common haplotype diversity were used to genotype well characterised PSP and CBD case-control cohorts. In addition to strong association with PSP and CBD of individual SNPs, two common haplotypes derived from these htSNPs were identified that are highly associated with PSP: the sole H2 derived haplotype was underrepresented and one of the common H1 derived haplotypes was highly associated, with a similar trend observed in CBD. There were powerful and highly significant associations with PSP and CBD of haplotypes formed by three H1 specific SNPs. This made it possible to define a candidate region of at least approximately 56 kb, spanning sequences from upstream of MAPT exon 1 to intron 9. On the H1 haplotype background, these could harbour the pathogenic variants. CONCLUSIONS: The findings support the pathological evidence that underlying variations in MAPT could contribute to disease pathogenesis by subtle effects on gene expression and/or splicing. They also form the basis for the investigation of the possible genetic role of MAPT in Parkinson's disease and other tauopathies, including Alzheimer's disease.

Hereditary motor and autonomic neuronopathy 1 maps to chromosome 20q13.2-13.3.

The spinal muscular atrophies (SMA) or hereditary motor neuronopathies result from the continuous degeneration and death of spinal cord lower motor neurons, leading to progressive muscular weakness and atrophy. We describe a large Brazilian family exhibiting an extremely rare, late-onset, dominant, proximal, and progressive SMA accompanied by very unusual manifestations, such as an abnormal sweating pattern, and gastrointestinal and sexual dysfunctions, suggesting concomitant involvement of the autonomic nervous system. We propose a new disease category for this disorder, 'hereditary motor and autonomic neuronopathy', and attribute the term, 'survival of motor and autonomic neurons 1' (SMAN1) to the respective locus that was mapped to a 14.5 cM region on chromosome 20q13.2-13.3 by genetic linkage analysis and haplotype studies using microsatellite polymorphic markers. This locus lies between markers D20S120 and D20S173 showing a maximum LOD score of 4.6 at D20S171, defining a region with 33 known genes, including several potential candidates. Identifying the SMAN1 gene should not only improve our understanding of the molecular mechanisms underlying lower motor neuron diseases but also help to clarify the relationship between motor and autonomic neurons.

Hereditary motor and autonomic neuronopathy 1 maps to chromosome 20q13.2-13.3

The spinal muscular atrophies (SMA) or hereditary motor neuronopathies result from the continuous degeneration and death of spinal cord lower motor neurons, leading to progressive muscular weakness and atrophy. We describe a large Brazilian family exhibiting an extremely rare, late-onset, dominant, proximal, and progressive SMA accompanied by very unusual manifestations, such as an abnormal sweating pattern, and gastrointestinal and sexual dysfunctions, suggesting concomitant involvement of the autonomic nervous system. We propose a new disease category for this disorder, `hereditary motor and autonomic neuronopathy', and attribute the term, `survival of motor and autonomic neurons 1' (SMAN1) to the respective locus that was mapped to a 14.5 cM region on chromosome 20q13.2-13.3 by genetic linkage analysis and haplotype studies using microsatellite polymorphic markers. This locus lies between markers D20S120 and D20S173 showing a maximum LOD score of 4.6 at D20S171, defining a region with 33 known genes, including several potential candidates. Identifying the SMAN1 gene should not only improve our understanding of the molecular mechanisms underlying lower motor neuron diseases but also help to clarify the relationship between motor and autonomic neurons.

Genetic approaches to solving common diseases.

The pathway to solving simple Mendelian inherited neurological disease is now well established. Barely a month goes by without new linkage data or mutations in a novel gene being reported. These developments are giving insights into a range of neurological conditions from the cortex to the muscle. However, most of these diseases are individually rare, and one of the major challenges facing neuroscience is to devise methods to find the genetic variants that confer risk of common diseases and differential response to treatment. This latter area is an important emerging field known as pharmacogenomics. Unlike Mendelian genetics where effective strategies are well established, the strategies for detecting moderate genetic effects in populations have been problematic. It is likely that a combination of techniques will be used, involving both linkage analysis and linkage disequilibrium mapping. In this review we consider some of the approaches that can be taken to resolve the common genetic variation underlying common disease.

PINK1 (PARK6) associated Parkinson disease in Ireland.

Mutations in the PINK1 gene have recently been shown to cause autosomal recessive Parkinson disease (PD). The authors assessed the prevalence of PINK1 gene mutations in 290 well-characterized early- and late-onset PD patients from Ireland. In a 51-year-old PD patient with a family history of PD, the authors identified a novel heterozygous mutation (R147H) in exon 2 of the PINK1 gene. Overall, these data indicate that PINK1 mutations are a rare cause of PD in Ireland.

Tau gene and Parkinson's disease: a case-control study and meta-analysis.

OBJECTIVE: To investigate whether the tau H1 haplotype is a genetic risk factor in Parkinson's disease and to report a meta-analysis on all previously published data METHODS: and results: In a sample of 580 patients with Parkinson's disease and 513 controls there was an increased risk of Parkinson's disease for both the tau H1 haplotype (p

DJ-1 mutations in Parkinson's disease.

Mutations in the DJ-1 gene have recently been shown to cause autosomal recessive Parkinson's disease. To estimate the prevalence of this mutation, an analysis was undertaken of 39 index cases of Parkinson's disease in whom a family history suggested autosomal recessive inheritance. No DJ-1 mutations were found in these patients, indicating that this gene is unlikely to be of numerical significance in clinical practice. The hypothesis was also tested that young onset Parkinson's disease patients in whom, despite extensive analysis, only a single heterozygous parkin mutation was found, might harbour a second mutation in the DJ-1 gene--that is, digenic inheritance. No patient was found with a single mutation in both DJ-1 and parkin genes, making this mode of inheritance unlikely. Finally it was confirmed that PARK6 and PARK7 (DJ-1), despite being phenotypically similar and mapping to the same small chromosomal region of 1p36, are caused by mutations in separate genes.

First application of preimplantation genetic diagnosis to neurofibromatosis type 2 (NF2).

Neurofibromatosis type 2 (NF2) is a dominantly inherited cancer predisposition syndrome that is caused bymutations in the NF2 gene. We report here the first clinical preimplantation genetic diagnosis (PGD) forNF2. A protocol was developed to simultaneously amplify the mutation and a single nucleotide polymorphism (SNP) located within the gene. The mutation and polymorphism were analysed by simultaneous fluorescent single-strand conformation polymorphism (SSCP) on an automated DNA sequencer. The mutation, carried by the male partner, was a single base pair substitution affecting a splice site in intron 4 of the gene. The female partner was infertile due to polycystic ovary syndrome and would require IVF to conceive. The couple was found to be informative at a linked intragenic SNP situated in the 5' untranslated region of the gene. The SNP was included in the assay to reduce the risk of misdiagnosis due to allele dropout (ADO). The couple underwent three cycles of treatment during which a total of 43 blastomeres were biopsied from 31 embryos. Amplification at both loci was obtained in 35 cells (81%). A total of five embryos were transferred, two in the first cycle, two in the second and one in the third. No pregnancy ensued. The results of the diagnoses indicated that, in this couple, the inheritance of the mutation may be non-Mendelian. Out of a total of 32 embryos tested only four were found not to carry the mutation. The reasons for this apparent skew remain unknown.

Pregnancy following preimplantation genetic diagnosis for Crouzon syndrome.

Crouzon syndrome is a dominantly inherited craniosynostosis syndrome which is caused by mutations in the fibroblast growth factor receptor 2 gene (FGFR2). However, a specific point mutation in the FGFR3 gene has also been shown to result in Crouzon syndrome associated with acanthosis nigricans. We report here the first method for preimplantation genetic diagnosis (PGD) of Crouzon syndrome based on multiplex PCR amplification followed by the direct detection of the causative mutation by single-stranded conformational polymorphism (SSCP) analysis. A highly polymorphic short tandem repeat (STR) locus was simultaneously analysed as a control against some forms of contamination. The mutation, carried by the female partner, was a de-novo substitution at codon 338 of the FGFR2 gene. The couple were found to be informative at the D21S11 STR locus. Two clinical PGD cycles were performed, resulting in the biopsy of 36 blastomeres, 25 of which showed amplification at the FGFR2 locus. All of the cells showed expected genotypes at the D21S11 locus with only one incidence of allele drop-out. A total of five embryos were transferred, two in the first cycle and three in the second, resulting in a singleton pregnancy.

Preimplantation genetic diagnosis of the fragile X syndrome by use of linked polymorphic markers.

Fragile X syndrome is the most common cause of familial mental retardation. The most common mutation is expansion of a triplet (CGG)(n) repeat in the 5' untranslated region of the FMR1 gene on Xq27.3. The expansion is refractory to PCR due to preferential amplification of the smaller allele in heterozygous cells and the high GC content of the repeat and surrounding sequences. Direct detection of the normal parental alleles in preimplantation embryos has been used for preimplantation genetic diagnosis (PGD) of this disorder. However, this approach is only suitable for approximately 63% of couples due to the heterozygosity of the repeat in the normal population. As an alternative we investigated the use of polymorphic markers flanking the mutation to track the normal and premutation carrying maternal chromosomes in preimplantation embryos. Using a panel of 11 polymorphisms, six (CA)(n) repeats and five single nucleotide polymorphisms, diagnosis was developed for 90% of referred couples. Multiplex amplification of informative markers was tested in 300 single buccal cells from interested couples with efficiency and allele drop out (ADO) rates ranging from 69% to 96% and 6% to 18%, respectively. Use of this approach is accurate and applicable to a larger number of patients at risk of transmitting fragile X to their offspring.

Primary mediastinal liposarcoma: a case report and review of the literature.

A case of mediastinal liposarcoma (LPS) in a 49-year-old female is described. Primary LPS of the mediastinum are very rare tumors. They occur mainly in adults but may be encountered in children. They are characterized by their large size and their variable histologic subtypes, which correlate with the clinical behavior and the prognosis. The radiologic features are nonspecific but are suggestive of the diagnosis. A tissue biopsy is needed for the final diagnosis. The treatment of choice is surgical with wide margin resection. Chemotherapy and radiotherapy are ineffective modalities, used in unresectable or incompletely resected tumors. The prognosis depends on the histologic subtypes and completeness of surgical excision.