Increased markers of cardiac vagal activity in leucine-rich repeat kinase 2-associated Parkinson's disease.

PurposeCardiac autonomic dysfunction manifests as reduced heart rate variability (HRV) in idiopathic Parkinson's disease (PD), but no significant reduction has been found in PD patients who carry the LRRK2 mutation. Novel HRV features have not been investigated in these individuals. We aimed to assess cardiac autonomic modulation through standard and novel approaches to HRV analysis in individuals who carry the LRRK2 G2019S mutation.MethodsShort-term electrocardiograms were recorded in 14 LRRK2-associated PD patients, 25 LRRK2-non-manifesting carriers, 32 related non-carriers, 20 idiopathic PD patients, and 27 healthy controls. HRV measures were compared using regression modeling, controlling for age, sex, mean heart rate, and disease duration. Discriminant analysis highlighted the feature combination that best distinguished LRRK2-associated PD from controls.ResultsBeat-to-beat and global HRV measures were significantly increased in LRRK2-associated PD patients compared with controls (e.g., deceleration capacity of heart rate: p = 0.006) and idiopathic PD patients (e.g., 8th standardized moment of the interbeat interval distribution: p = 0.0003), respectively. LRRK2-associated PD patients also showed significantly increased irregularity of heart rate dynamics, as quantified by Rényi entropy, when compared with controls (p = 0.002) and idiopathic PD patients (p = 0.0004). Ordinal pattern statistics permitted the identification of LRRK2-associated PD individuals with 93% sensitivity and 93% specificity. Consistent results were found in a subgroup of LRRK2-non-manifesting carriers when compared with controls.ConclusionsIncreased beat-to-beat HRV in LRRK2 G2019S mutation carriers compared with controls and idiopathic PD patients may indicate augmented cardiac autonomic cholinergic activity, suggesting early impairment of central vagal feedback loops in LRRK2-associated PD

Neurodegeneration: Potential Causes, Prevention, and Future Treatment Options

Here I advance a hypothesis that neurodegeneration is a natural process associated with aging due to the loss of genetic redundancy following a mathematical model R(t) = R0(1-αe(βC+γI+δEt)t), where the calorie intake (C) and immune response (I) play critical roles. The early onset of neurodegenerative diseases such as Alzheimer’s disease is due to metabolic imbalance or chronic immune reactions to various infections. Therefore, the potential treatment options for neurodegenerative diseases are to modulate metabolism and immune response

Rare variants in LRRK1 and Parkinson's disease

Approximately 20 % of individuals with Parkinson's disease (PD) report a positive family history. Yet, a large portion of causal and disease-modifying variants is still unknown. We used exome sequencing in two affected individuals from a family with late-onset PD to identify 15 potentially causal variants. Segregation analysis and frequency assessment in 862 PD cases and 1,014 ethnically matched controls highlighted variants in EEF1D and LRRK1 as the best candidates. Mutation screening of the coding regions of these genes in 862 cases and 1,014 controls revealed several novel non-synonymous variants in both genes in cases and controls. An in silico multi-model bioinformatics analysis was used to prioritize identified variants in LRRK1 for functional follow- up. However, protein expression, subcellular localization, and cell viability were not affected by the identified variants. Although it has yet to be proven conclusively that variants in LRRK1 are indeed causative of PD, our data strengthen a possible role for LRRK1 in addition to LRRK2 in the genetic underpinnings of PD but, at the same time, highlight the difficulties encountered in the study of rare variants identified by next-generation sequencing in diseases with autosomal dominant or complex patterns of inheritance

Phenotypic Characteristics of Zambian patients with Parkinson's Disease

Objective: To describe the phenotypic characteristics of adult Zambian patients with newly diagnosed Parkinson's disease (PD) at University Teaching Hospital (UTH).Background: The genetic basis of idiopathic Parkinson's disease is remains unknown. Little information is available regarding the genotype and phenotypic characteristics of PD among people of African origin.Methods: Subjects with PD were recruited from the neurology clinic from January 2010, through April 2011. Parkinson's disease diagnosis was established according to standard criteria. Only ethnic Zambian patients were included to the study. The disease was considered familial when one or more first to third degree relatives were affected with PD. Extensive pedigree was constructed for all familial and sporadic cases. Unrelated healthy controls (spouses, volunteers) were free of PD and other movement disorders. Genomic DNA was extracted from peripheral blood leukocytes according to standard procedures from patients and controls, respectively.Results: In total 46 patients for phenotype and 46 controls were matched with patients for age, gender, and area of residence. The mean age of patients at onset of the disease was 53.8 ±13.7years. Three patients had juvenile form PD and12 patients had early onset PD. In 31 patients the disease started after 50 years old. Tremor and bradykinesia were the most common initial symptoms. 26% had a history of first-and second-degree relatives affected with PD. Mean age were significantly lower in patients with familial PD (47.7±7.3) than sporadic disease (62,5±5.4) (p>0.001). In 8 families (66.6%) the disease had autosomal dominant and in 4 families (33.3%) autosomal recessive inheritance. Age at onset was significantly lower (27 years) in patients with autosomal recessive transmission than in patients with autosomal dominant inheritance. The disease duration was significantly longer in patients with autosomal recessive inheritance (11.2 years) than in patients with autosomal dominant inheritance (3 years).Conclusions: This study represents phenotypic description of Zambian patients with PD recruited in clinical based manner. The majority of our patients were characterized tremor-dominant or akineticrigid types of the disease. Age at onset of PD was younger as compared to European population. The disease has both autosomal dominant and autosomal recessive inheritance. The familial aggregation of PD warrant further studies of genetic and environmental risk factors n the Zambian population.Keywords: Phenotype, Parkinson's disease, Zambian adult

The promise of genome‐wide SNP genotyping: from population genetics to disease gene identification

Advances in single nucleotide polymorphism (SNP) genotyping technologies have revolutionised our ability to scrutinise the human genome. My PhD research focuses on using these new technologies to catalogue genetic variability in a collection of diverse populations from around the globe, and to determine the role of genetic variants in neurological diseases. First, I present and discuss the analysis of genome‐wide SNP data in individuals from ethnically and geographically diverse human populations uncovering the diversity of genotype, haplotype and copy number variation in these populations. Second, I will describe an autozygosity mapping approach in three Brazilian dystoniaparkinsonism families which lead to the identification of a novel disease‐segregating mutation in the gene PRKRA. Third, I will report on a large genome‐wide association study in Parkinson’s disease, uncovering genetic variability at the SNCA and MAPT loci that are strongly associated with risk for developing disease. Forth, I provide compelling evidence that genetic variants at the SNCA locus are also significantly associated with risk for developing multiple system atrophy. This finding represents the first reproducible risk gene for this devastating disorder, and causally links this condition to the more common neurodegenerative disorder Parkinson’s disease. Finally, I present the results of a comprehensive mutational screening study investigating the frequency and spectrum of sequence and copy number mutations in the parkinsonism genes PRKN and PINK in individuals with early-onset Parkinson’s disease, in multiple system atrophy patients and in normal controls. In summary, the data presented in this thesis emphasise the critical role that genetic variability plays in the pathogenesis of neurological disorders

Genetic analysis of Parkinson's disease using Next-generation sequencing

Neurological diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), Epilepsy and Multiple Sclerosis are included in the Global burden of disease study as these disorders have a high impact on public health. Lack of effective treatment has motivated the researchers to perform early diagnostics, by identifying new gene mutations, which can improve the therapies. The aim of this thesis was a genetic analysis of PD using next-generation sequencing data. In this thesis, whole genome sequencing (WGS) and whole exome sequencing (WES) using DNA from familial PD patients and healthy individuals was performed in order to identify the PD causal genes. A large repository of sporadic PD WES data and a genotyping array was used to replicate our findings. The PD patients from Germany were stratified for clinical trials on the basis of mitochondrial endo-phenotype by performing risk profiling of associated Single Nucleotide Polymorphisms (SNPs) using exome genotyping array. The sporadic PD WES and genotyping array data from International Parkinson’s disease Genomics Consortium was used to perform association tests, to determine the burden of rare variants in candidate genes of interest. Furthermore, mRNA sequencing of all the genes under the PD GWAS loci after knockdown with short hairpin RNAs was performed, to identify the actual genes contributing to PD risk and the novel pathways involved in PD. Finally, an epistatic interaction of a Mendelian PD gene and associated locus was performed to understand the joint contribution to PD risk. Taking everything into account, we identified pathogenic variants in known and some novel genes causing PD in families. On the basis of risk profiling some of the German PD patients will undergo clinical trials with coenzyme Q10 and vitamin K2. The association tests using sporadic PD data helped to identify some novel genes significantly associated with PD risk. The knockdown experiments facilitated the identification of genes contributing to PD risk in some of the PD GWAS loci

Autophagy and stress granules: the merging of two pathways in Parkinson's disease

Autophagy is compromised in Parkinson’s disease (PD) with a number of PD-associated genetic mutations leading to its dysregulation. Leucine-rich repeat kinase (LRRK2) mutations, causative of PD, aberrantly enhance autophagy. Our lab elucidated a LRRK2 gene regulatory network identifying transcripts showing coordinated expression level changes associated with PD. Histone deacetylase 6 (HDAC6) was found to be an important interactor with LRRK2, regulating many of the same transcripts. The majority of these transcripts associate with autophagy and the lysosomal complex. I hypothesized that LRRK2 interacts with HDAC6 to regulate autophagy. Silencing of HDAC6 in SH-SY5Y normalized the autophagosomal size altered by expression of PD-linked LRRK2 mutants. This work identified a key role for HDAC6 in mediating the autophagic dysfunction induced by the mutant LRRK2. In addition to autophagy, stress granule (SG) formation has emerged as a compelling mechanism in the pathogenesis of PD. RNA-binding proteins (RBPs), such as T-cell intracellular antigen-1 (TIA-1), are major component of SGs. I observed TIA-1 translocating from the nucleus to the cytoplasm in PD cortex without forming SGs. Hu antigen D (HuD) also showed changes, with the RBP more present in the cytoplasm than the nucleus in PD with no SGs observed. These preliminary studies lead to the hypothesis that low levels of SGs result from an inhibition by alpha-synuclein (syn), or hyperactive autophagy. For that purpose, brain tissues from a mouse model of PD (A53T-syn transgenic mouse) were examined by immunohistochemistry. There was no difference in TIA-1 expression in control and A53T-syn expressing mouse brains, or SG formation in primary neurons after treatment with recombinant A53T fibrils. To determine whether the lack of SGs in PD brain was due to activation of autophagy, BE-M17 cells were treated with rapamycin, an autophagy activator, which decreased SGs by 50%. Overexpression of TIA-1 in BE-M17 cells under arsenite treatment also increased autophagosomal size by 50%, indicating co-regulation of SGs and autophagy. My work indicates that the pathophysiology of PD is associated with a loss of SGs due to elevated activity of autophagy, presumably due to PD-linked LRRK2 mutations. This co-regulatory network may be a potential therapeutic target of PD