Abi Li

Glucocerebrosidase mutations in clinical and pathologically proven Parkinson's disease

Mutations in the glucocerebrosidase gene (GBA) are associated with Gauchers disease, the most common lysosomal storage disorder. Parkinsonism is an established feature of Gauchers disease and an increased frequency of mutations in GBA has been reported in several different ethnic series with sporadic Parkinsons disease. In this study, we evaluated the frequency of GBA mutations in British patients affected by Parkinsons disease. We utilized the DNA of 790 patients and 257 controls, matched for age and ethnicity, to screen for mutations within the GBA gene. Clinical data on all identified GBA mutation carriers was reviewed and analysed. Additionally, in all cases where brain material was available, a neuropathological evaluation was performed and compared to sporadic Parkinsons disease without GBA mutations. The frequency of GBA mutations among the British patients (33/790 = 4.18%) was significantly higher (P = 0.01; odds ratio = 3.7; 95% confidence interval = 1.12-12.14) when compared to the control group (3/257 = 1.17%). Fourteen different GBA mutations were identified, including three previously undescribed mutations, K7E, D443N and G193E. Pathological examination revealed widespread and abundant alpha-synuclein pathology in all 17 GBA mutation carriers, which were graded as Braak stage of 5-6, and had McKeiths limbic or diffuse neocortical Lewy body-type pathology. Diffuse neocortical Lewy body-type pathology tended to occur more frequently in the group with GBA mutations compared to matched Parkinsons disease controls. Clinical features comprised an early onset of the disease, the presence of hallucinations in 45% (14/31) and symptoms of cognitive decline or dementia in 48% (15/31) of patients. This study demonstrates that GBA mutations are found in British subjects at a higher frequency than any other known Parkinsons disease gene. This is the largest study to date on a non-Jewish patient sample with a detailed genotype/phenotype/pathological analyses which strengthens the hypothesis that GBA mutations represent a significant risk factor for the development of Parkinsons disease and suggest that to date, this is the most common genetic factor identified for the disease.

Characterization of PLA2G6 as a locus for dystonia-parkinsonism.

Although many recessive loci causing parkinsonism dystonia have been identified, these do not explain all cases of the disorder.

SNCA Variants Are Associated with Increased Risk for Multiple System Atrophy

To test whether the synucleinopathies Parkinsons disease and multiple system atrophy (MSA) share a common genetic etiology, we performed a candidate single nucleotide polymorphism (SNP) association study of the 384 most associated SNPs in a genome‐wide association study of Parkinsons disease in 413 MSA cases and 3,974 control subjects. The 10 most significant SNPs were then replicated in additional 108 MSA cases and 537 controls. SNPs at the SNCA locus were significantly associated with risk for increased risk for the development of MSA (combined p = 5.5 × 1012; odds ratio 6.2). Ann Neurol 2009;65:610–614

Widespread Lewy body and tau accumulation in childhood and adult onset dystonia-parkinsonism cases with PLA2G6 mutations

The 2 major types of neurodegeneration with brain iron accumulation (NBIA) are the pantothenate kinase type 2 (PANK2)-associated neurodegeneration (PKAN) and NBIA2 or infantile neuroaxonal dystrophy (INAD) due to mutations in the phospholipase A2, group VI (PLA2G6) gene. We have recently demonstrated clinical heterogeneity in patients with mutations in the PLA2G6 gene by identifying a poorly defined subgroup of patients who present late with dystonia and parkinsonism. We report the clinical and genetic features of 7 cases with PLA2G6 mutations. Brain was available in 5 cases with an age of death ranging from 8 to 36 years and showed widespread alpha-synuclein-positive Lewy pathology, which was particularly severe in the neocortex, indicating that the Lewy pathology spread corresponded to Braak stage 6 and was that of the “diffuse neocortical type”. In 3 cases there was hyperphosphorylated tau accumulation in both cellular processes as threads and neuronal perikarya as pretangles and neurofibrillary tangles. Later onset cases tended to have less tau involvement but still severe alpha-synuclein pathology. The clinical and neuropathological features clearly represent a link between PLA2G6 and parkinsonian disorders.

Dysregulation of glucose metabolism is an early event in sporadic Parkinson's disease

Unlike most other cell types, neurons preferentially metabolize glucose via the pentose phosphate pathway (PPP) to maintain their antioxidant status. Inhibiting the PPP in neuronal cell models causes cell death. In rodents, inhibition of this pathway causes selective dopaminergic cell death leading to motor deficits resembling parkinsonism. Using postmortem human brain tissue, we characterized glucose metabolism via the PPP in sporadic Parkinsons disease (PD), Alzheimers disease (AD), and controls. AD brains showed increased nicotinamide adenine dinucleotide phosphate (NADPH) production in areas affected by disease. In PD however, increased NADPH production was only seen in the affected areas of late-stage cases. Quantifying PPP NADPH-producing enzymes glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase by enzyme-linked immunosorbent assay, showed a reduction in the putamen of early-stage PD and interestingly in the cerebellum of early and late-stage PD. Importantly, there was no decrease in enzyme levels in the cortex, putamen, or cerebellum of AD. Our results suggest that down-regulation of PPP enzymes and a failure to increase antioxidant reserve is an early event in the pathogenesis of sporadic PD.

GLUCOCEREBROSIDASE MUTATIONS IN 108 NEUROPATHOLOGICALLY CONFIRMED CASES OF MULTIPLE SYSTEM ATROPHY

Parkinson disease (PD), Lewy body dementia (LBD), and multiple system atrophy (MSA) are synucleinopathies whose primary pathogenic event is the deposition of inclusions composed of aberrantly fibrillized α-synuclein.1 In PD and LBD, Lewy bodies are the key aggregate, whereas in MSA, α-synuclein accumulates in the form of oligodendroglial and neuronal cytoplasmic inclusions (GCIs and NCIs).2,3 Parkinsonian manifestations have been noted in a subset of patients with Gaucher disease and there is evidence that parkinsonism is more frequent among carrier relatives of patients with Gaucher disease.4 In a remarkable study, the glucocerebrosidase (GBA) gene was sequenced in an American PD brain bank series where GBA mutations were detected at a much higher frequently than in controls (PD 21% vs control 4.5%).5 These findings have since been replicated, mainly in Ashkenazi patient groups who have a higher mutation frequency but also in patients with clinically and pathologically diagnosed PD and LBD in a number of studies in different populations.4 In a study of 75 neuropathologically confirmed synucleinopathies, GBA mutations were found in 23% of the cases with Lewy bodies.6 The frequency of GBA mutations around the world between 2.3 and 31% (depending on population) indicates that GBA mutations are one of the commonest genetic risk factors for PD. GBA mutation carriers have a wide spectrum of phenotypes, ranging from classic l-dopa-responsive PD to LBD. In neuropathologic studies of PD/LBD cases, GBA mutations, α-synuclein inclusions, and Lewy bodies have been seen. This spectrum of clinical and pathologic features would suggest that MSA should also be a candidate to have GBA mutation.3 Only 12 cases of MSA have been analyzed for GBA mutations and defects were seen in this handful of cases.6 We extracted DNA from the brain tissue of 108 neuropathologically confirmed British MSA cases that had been diagnosed according to brain bank criteria and 257 normal British controls. Mean age at onset was 58.2 ± 10.7 years (range 34–83), mean age at death 64.5 ± 10.2 years (39–87), mean disease duration 6.8 ± 2.9 years (2–16), and 48% were men. All exons and flanking intronic regions of the GBA gene were sequenced in MSA and control cases. To avoid amplifying and sequencing the GBA pseudogene we employed long range GBA PCR and then BigDye sequencing as previously described.7 In our MSA study group of 108 cases, we identified one heterozygous GBA mutation (c.904C>T; R262H), giving a mutation frequency of 0.92%. In the British controls, three heterozygous mutations (V497L, N409S, and R269Q) out of 257 cases were identified (1.17%). There was no significant difference between the two groups (p = 0.66). The single MSA case with the heterozygous R262H mutation was a woman with an age at onset of 44 years. She had parkinsonian, cerebellar, and autonomic features (MSA–mixed type) with no family history. She died at age 51 years and the neuropathology revealed widespread GCIs and NCIs with a predominance in striatonigral structures. There were no Lewy bodies. One limitation of our study is the small sample size. Our study has a power of 80% to detect variants with an OR >1.61 or <0.63 at a significance level of 0.05. The results of this study indicate that GBA mutations are not common etiologic players in Caucasian patients with MSA. We cannot exclude that GBA mutations confer modest or low risk to disease. Furthermore, we did not sequence risk variants in regulatory regions (such as the promotor region or untranslated regions). Mutations in these regions would therefore have been missed. The unexpected role of GBA mutations has been demonstrated in several populations and is undoubtedly a highly significant risk factor for PD and LBD. More importantly, GBA mutations reveal a direct link between the lysosomal protein pathway and the clearance or the development of α-synuclein aggregates into Lewy bodies. Our study indicates that GBA mutations are not associated with MSA in the population that we analyzed, and that this branch of the ceramide pathway is unlikely to be associated with all types of primary α-synuclein deposition.

Review: Insights into molecular mechanisms of disease in neurodegeneration with brain iron accumulation: unifying theories

Neurodegeneration with brain iron accumulation (NBIA) is a group of disorders characterized by dystonia, parkinsonism and spasticity. Iron accumulates in the basal ganglia and may be accompanied by Lewy bodies, axonal swellings and hyperphosphorylated tau depending on NBIA subtype. Mutations in 10 genes have been associated with NBIA that include Ceruloplasmin (Cp) and ferritin light chain (FTL), both directly involved in iron homeostasis, as well as Pantothenate Kinase 2 (PANK2), Phospholipase A2 group 6 (PLA2G6), Fatty acid hydroxylase 2 (FA2H), Coenzyme A synthase (COASY), C19orf12, WDR45 and DCAF17 (C2orf37). These genes are involved in seemingly unrelated cellular pathways, such as lipid metabolism, Coenzyme A synthesis and autophagy. A greater understanding of the cellular pathways that link these genes and the disease mechanisms leading to iron dyshomeostasis is needed. Additionally, the major overlap seen between NBIA and more common neurodegenerative diseases may highlight conserved disease processes. In this review, we will discuss clinical and pathological findings for each NBIA‐related gene, discuss proposed disease mechanisms such as mitochondrial health, oxidative damage, autophagy/mitophagy and iron homeostasis, and speculate the potential overlap between NBIA subtypes.

Alterations in global DNA methylation and hydroxymethylation are not detected in Alzheimer's disease.

Genetic factors do not seem to account fully for Alzheimer disease (AD) pathogenesis. There is evidence for the contribution of environmental factors, whose effect may be mediated by epigenetic mechanisms. Epigenetics involves the regulation of gene expression independently of DNA sequence and these epigenetic changes are influenced by age and environmental factors, with DNA methylation being one of the best characterized epigenetic mechanisms. The human genome is predominantly methylated on CpG motifs, which results in gene silencing; however methylation within the body of the gene may mark active transcription. There is evidence suggesting an involvement of environmental factors in the pathogenesis of Alzheimers disease (AD), which prompted our study examining DNA methylation in this disorder.

An ITPR1 gene deletion causes spinocerebellar ataxia 15/16: a genetic, clinical and radiological description.

the purpose of this study was to characterise a novel family with very slowly progressive pure spinocerebellar ataxia (SCA) caused by a deletion in the inositol 1,4,5‐triphosphate receptor 1 (ITPR1) gene on chromosome 3. This is a detailed clinical, genetic, and radiological description of the genotype. Deletions in ITPR1 have been shown to cause SCA15/SCA16 in six families to date. A further Japanese family has been identified with an ITPR1 point mutation. The exact prevalence is as yet unknown, but is probably higher than previously thought. The clinical phenotype of the family is described, and videotaped clinical examinations are presented. Serial brain magnetic resonance imaging studies were carried out on one affected individual, and genetic analysis was performed on several family members. Protein analysis confirmed the ITPR1 deletion. Affected subjects display a remarkably slow, almost pure cerebellar syndrome. Serial magnetic resonance imaging shows moderate cerebellar atrophy with mild inferior parietal and temporal cortical volume loss. Genetic analysis shows a deletion of 346,487 bp in ITPR1 (the second largest ITPR1 deletion reported to date), suggesting SCA15 is due to a loss of ITPR1 function. Western blotting of lymphoblastoid cell line protein confirms reduced ITPR1 protein levels. SCA15 is a slowly or nonprogressive pure cerebellar ataxia, which appears to be caused by a loss of ITPR1 function and a reduction in the translated protein. Patients with nonprogressive or slowly progressive ataxia should be screened for ITPR1 defects.

Neuropathy target esterase impairments cause Oliver–McFarlane and Laurence–Moon syndromes

Background Oliver–McFarlane syndrome is characterised by trichomegaly, congenital hypopituitarism and retinal degeneration with choroidal atrophy. Laurence–Moon syndrome presents similarly, though with progressive spinocerebellar ataxia and spastic paraplegia and without trichomegaly. Both recessively inherited disorders have no known genetic cause. Methods Whole-exome sequencing was performed to identify the genetic causes of these disorders. Mutations were functionally validated in zebrafish pnpla6 morphants. Embryonic expression was evaluated via in situ hybridisation in human embryonic sections. Human neurohistopathology was performed to characterise cerebellar degeneration. Enzymatic activities were measured in patient-derived fibroblast cell lines. Results Eight mutations in six families with Oliver–McFarlane or Laurence–Moon syndrome were identified in the PNPLA6 gene, which encodes neuropathy target esterase (NTE). PNPLA6 expression was found in the developing human eye, pituitary and brain. In zebrafish, the pnpla6 curly-tailed morphant phenotype was fully rescued by wild-type human PNPLA6 mRNA and not by mutation-harbouring mRNAs. NTE enzymatic activity was significantly reduced in fibroblast cells derived from individuals with Oliver–McFarlane syndrome. Intriguingly, adult brain histology from a patient with highly overlapping features of Oliver–McFarlane and Laurence–Moon syndromes revealed extensive cerebellar degeneration and atrophy. Conclusions Previously, PNPLA6 mutations have been associated with spastic paraplegia type 39, Gordon–Holmes syndrome and Boucher–Neuhäuser syndromes. Discovery of these additional PNPLA6-opathies further elucidates a spectrum of neurodevelopmental and neurodegenerative disorders associated with NTE impairment and suggests a unifying mechanism with diagnostic and prognostic importance.