Analysis of LRRK 2 G 2019 S and I 2020 T mutations in Parkinson's disease

Mutations in the leucine-rich repeat kinase 2 (LRRK 2), encoding dardarin protein, have been demonstrated to be linked to autosomal dominant Parkinson's disease (PD). In the present study the entire exon 41 of LRRK 2 gene was evaluated in a series of 174 PD patients recruited from Polish population, aged at the time of diagnosis 54.0+/-39.1 years, 21 of them had positive family history of PD with mean onset of the disease of 51.9+/-11.7 years as well as in 190 healthy controls aged 73.7+/-6.0 years. The mutations were evaluated by direct sequencing for mutations in exon 41 of LRRK 2 gene. In the studied patients no known mutations in exon 41 of LRRK 2 gene, including G 2019 S and I 2020 T were found, both in PD patients as well as in the controls. It can be concluded that the G 2019 S and I 2020 T mutations in exon 41 of LRRK 2 gene are rare causes of Parkinson disease in a Polish population.     

Alpha-synuclein missense and multiplication mutations in autosomal dominant Parkinson's disease

Missense mutations and genomic multiplications of the alpha-synuclein gene (SNCA) have been linked to autosomal dominant familial Parkinson's disease. We screened 50 probands of families with autosomal dominant parkinsonism for alpha-synuclein mutations by exon sequencing. No known or novel mutations were found. We also analyzed the genomic DNA for multiplications of the SNCA locus using multiplex panels of microsatellite markers. All samples were diploid with two normal copies of the SNCA locus. Hence, alpha-synuclein missense mutations and SNCA genomic multiplications remain a rare cause of disease.     

Screening for VPS35 mutations in Parkinson's disease

Recently 2 groups have independently identified a mutation in the gene 'vacuolar protein sorting 35 homolog' (VPS35 c.1858G>A; p.Asp620Asn) as a possible cause of autosomal dominant Parkinson's disease (PD). In order to assess the frequency of the reported mutation and to search for other possible disease-causing variants in this gene, we sequenced all 17 exons of VPS35 in 96 familial PD cases, and exon 15 (in which the reported mutation is found) in an additional 64 familial PD cases, 175 young-onset PD cases, and 262 sporadic, neuropathologically confirmed PD cases. We identified 1 individual with the p.Asp620Asn mutation and an autosomal dominant family history of PD. Subsequent follow-up of the family confirmed an affected sibling and cousin who also carried the same mutation. No other potentially disease-causing mutations were identified. We conclude that the VPS35 c.1858G>A mutation is an uncommon cause of familial Parkinson's disease in our population.     

Clinicogenetic study of GBA mutations in patients with familial Parkinson's disease

The glucocerebrosidase gene (GBA) is a known risk factor of Parkinson's disease (PD). We sequenced entire coding exons and exon/intron boundaries of GBA in 147 Japanese familial PD (FPD) patients from 144 families and 100 unrelated control subjects. Twenty-seven of 144 (18.8%) of index patients were heterozygous for known Gaucher disease mutations, suggesting that GBA heterozygous mutations are strongly associated with FPD (odds ratio = 22.9, 95% confidence interval = 3.1–171.2). The frequency was significantly higher in autosomal dominant PD (ADPD) compared with autosomal recessive PD. According to clinical assessments, PD patients with GBA mutations exhibited typical manifestations of PD or dementia with Lewy bodies (DLB), such as L-dopa responsive parkinsonism with psychiatric problems and/or cognitive decline. Interestingly, they also presented with reduced myocardial ¹²³I-metaiodobenzylguanidine uptake. Our findings suggest that heterozygous GBA mutations are strong risk factors in FPD, especially for autosomal dominant PD. Some patients with GBA heterozygous mutations develop clinical features of DLB. We speculate that GBA dysfunction may promote Lewy body formation, resulting in more severe PD or DLB phenotypes that are inherited in families.     

Absence/rarity of commonly reported LRRK2 mutations in Indian Parkinson's disease patients

Recent discovery of pathogenic mutations in the leucine-rich repeat kinase 2 (LRRK2) gene in Parkinson's disease (PD) patients in different ethnic groups have raised a hope of diagnostic screening and genetic counseling. We investigated the six most commonly reported mutations in LRRK2 gene among Indian PD patients, using PCR-RFLP method. Mutations G2019S, R1441C, R1441G, and R1441H were screened in 1012 individuals (PD, 800; controls, 212) while mutations I2012T and I2020T were screened in 748 PD patients. We did not observe any of these six mutations in this study sample except in a single female young onset PD patient who showed a heterozygous G2019S mutation. The absence of mutations was reconfirmed by sequencing of probands from several autosomal dominant PD families. Our observations suggest that these mutations may be a rare cause of PD among Indians and therefore of little help for diagnostic screening and genetic counseling for Indian PD patients.     

Low frequency of common LRRK2 mutations in Mexican patients with Parkinson's disease

Mutations in leucine-rich repeat kinase 2 gene (LRRK2) account for as much as 5–6% of familial Parkinson's disease (PD) and 1–2% of sporadic PD. These mutations represent the most frequent cause of autosomal dominant PD, particularly in certain ethnic groups. In this first report concerning LRRK2 mutations in Mexican-mestizos, we screened 319 consecutive PD patients (186 males; 133 females; mean age at onset: 52.4 years) for LRRK2 mutations in exons 31 and 41 and for the mutation in exon 35, which produces the Y1699C substitution. Three (0.94%) patients, two with sporadic PD and one with familial PD (disease mean age at onset, 53.3 years), were heterozygous for LRRK2 mutations. Of these three, two patients had one of two different mutations in exon 31 (R1441G and R1441H, respectively); the other patient carried the G2019S mutation in exon 41. The Y1699C mutation was absent from this PD sample. Four additional subjects, unaffected relatives of one PD patient with a mutation in LRRK2, were subsequently genetically tested. None of the three LRRK2 mutations identified was present in 200 neurologically healthy Mexican control individuals. These findings have important implications for molecular testing of LRRK2 mutations in Mexican PD patients.     

No pathogenic mutations in the beta-synuclein gene in Parkinson's disease.

We present 11 families consistent with autosomal dominant inheritance of probable Parkinson's disease (PD). Although excluded as a cause of disease in these kindreds, mutations in the alpha-synuclein gene have been implicated in familial PD. The beta-synuclein gene is highly homologous, expressed in the nervous system and thus is a good candidate gene for PD. Multipoint linkage analysis was either equivocal or excluded 5q35 haplotype sharing among affected family members. Sequencing the translated exons of the beta-synuclein gene failed to identify any pathogenic mutation.     

Lack of evidence for association of a UCH-L1 S18Y polymorphism with Parkinson's disease in a Han-Chinese population

Mutation in UCH-L1 has been reported as a rare cause of autosomal dominant Parkinson's disease (PD). A S18Y polymorphism in the same gene has been associated with sporadic PD. We investigated the frequency of this polymorphism among the Han-Chinese ethnic population in a case-control study. A total of 600 patients with PD and 334 unrelated healthy controls were genotyped using PCR-restriction fragment length polymorphism analysis. We did not observe any difference in allele or genotype frequencies between the cases and the controls (P>0.05). Our results do not support a role for this variant in sporadic PD.     

A wide variety of mutations in the parkin gene are responsible for autosomal recessive parkinsonism in Europe. French Parkinson's Disease Genetics Study Group and the European Consortium on Genetic Susceptibility in Parkinson's Disease

Autosomal recessive juvenile parkinsonism (AR-JP, PARK2; OMIM 602544), one of the monogenic forms of Parkinson's disease (PD), was initially described in Japan. It is characterized by early onset (before age 40), marked response to levodopa treatment and levodopa-induced dyskinesias. The gene responsible for AR-JP was recently identified and designated parkin. We have analysed the 12 coding exons of the parkin gene in 35 mostly European families with early onset autosomal recessive parkinsonism. In one family, a homozygous deletion of exon 4 could be demonstrated. By direct sequencing of the exons in the index patients of the remaining 34 families, eight previously undescribed point mutations (homozygous or heterozygous) were detected in eight families that included 20 patients. The mutations segregated with the disease in the families and were not detected on 110-166 control chromosomes. Four mutations caused truncation of the parkin protein. Three were frameshifts (202-203delAG, 255delA and 321-322insGT) and one a nonsense mutation (Trp453Stop). The other four were missense mutations (Lys161Asn, Arg256Cys, Arg275Trp and Thr415Asn) that probably affect amino acids that are important for the function of the parkin protein, since they result in the same phenotype as truncating mutations or homozygous exon deletions. Mean age at onset was 38 +/- 12 years, but onset up to age 58 was observed. Mutations in the parkin gene are therefore not invariably associated with early onset parkinsonism. In many patients, the phenotype is indistinguishable from that of idiopathic PD. This study has shown that a wide variety of different mutations in the parkin gene are a common cause of autosomal recessive parkinsonism in Europe and that different types of point mutations seem to be more frequently responsible for the disease phenotype than are deletions.     

PARK2 gene mutations in early onset Parkinson's disease patients of South India

With the etiology being unclear till date, a combination of age, genetic and environmental factors are known to play a significant role in the pathogenesis of Parkinson's disease. Mutations in PARK2 gene have been implicated to cause autosomal recessive early onset PD. We analyzed the 12 coding exons of PARK2 gene in 16 early onset PD patients of South Indian ethnicity. PARK2 mutations were present in 68% of the early onset cases. We report the presence of four PARK2 sequence variants c.1239G>C, c.171+25T>C, c.202A>G, c.601G>A, and a novel insertion mutation, c.798_799insA in the exon 7 of PARK2 gene. These results suggest that mutations in PARK2 gene may be a common cause of PD among South Indian early onset patients.     

Search for the PARK3 founder haplotype in a large cohort of patients with Parkinson's disease from Northern Germany

A founder haplotype on chromosome 2p for autosomal dominant Parkinson's disease (PD) has been postulated for two families of Northern European descent, and a new mutation in the α-synuclein gene (Ala30Pro) has been found in a German PD family. We evaluated 85 German PD patients and 85 ethnically matched controls for shared markers on chromosome 2p and for the new α-synuclein mutation. We found no evidence for linkage disequilibrium, suggesting that the putative founder mutation on chromosome 2p is not a common cause of PD in the local population. Furthermore, no patient carried the Ala30Pro change, supporting earlier findings that mutations in the α-synuclein gene are extremely rare.     

PLA2G6 variant in Parkinson's disease

PLA2G6 was reported recently as the causative gene for PARK14-linked autosomal recessive early-onset dystonia-parkinsonism. In a recent study in Singapore, heterozygous PLA2G6 p.P806R (c.2417C>G) mutation in exon 17 was reported to be a possible Parkinson's disease (PD)-related mutation. To determine the significance of the PLA2G6 mutation, we conducted an association study by performing direct sequencing of PLA2G6 exon 17 in 379 Japanese sporadic PD patients and 310 controls in the Japanese general population. In this group, we found 12 patients (12/379=3.16%) and 10 controls (10/310=3.23%) with a heterozygous p.P806R mutation (P=0.96, χ(2)=0.0019). Therefore, our large case-controlled study suggests that PLA2G6 p.P806R is not a disease-associated polymorphism in PD. Moreover, we performed direct sequencing of all exons and exon-intron boundaries of PLA2G6 in 116 Japanese patients with sporadic PD. Two single heterozygous variants (p.R301C or p.D331N) were found (both frequencies: 1/379 patients vs 0/310 controls) and the roles of their variants were unclear. Finally, combined with the previous report, our findings emphasize that PLA2G6 mutations are unlikely to be the major causes or risk factors of PD at least in Asian populations. However, further large studies in various populations are needed because patients with PLA2G6 mutations can show heterogeneous clinical features.     

A novel mutation in the PYGM gene in a family with pseudo-dominant transmission of McArdle disease

A Caucasian family appeared to transmit McArdle disease in an autosomal dominant manner and was examined for mutations in the myophosphorylase gene. The asymptomatic father was heterozygous for the R49X mutation in exon 1. The symptomatic mother was a compound heterozygote for R49X and a novel 2 bp deletion in exon 1 causing a frameshift at codon 25 (T25fs). Each of three children manifested symptoms of McArdle disease and was either a compound heterozygote for these two mutations or homozygous for R49X.     

Detection of alterations in all three exons of the peripherin/RDS gene in Swedish patients with retinitis pigmentosa using an efficient DGGE system.

AIMS: To develop a sensitive mutation screening procedure suitable for routine analysis of the peripherin/RDS gene, and to estimate the nature and prevalence of peripherin/RDS gene mutations in Swedish patients with autosomal dominant retinitis pigmentosa. METHODS: To make the method as sensitive as possible, as many as eight segments, covering the three exons and the flanking intron sequences of the peripherin/RDS gene, were analysed by denaturing gradient gel electrophoresis. A group of 38 Swedish patients with a clinical diagnosis of autosomal dominant retinitis pigmentosa were screened for mutations in the peripherin/RDS gene. RESULTS: Three point mutations were found in four of the patients and five polymorphisms were defined. One mutation in exon 1, R172W, has been described previously in other ethnic groups as causing a macular degeneration. Another mutation, in exon 2 and causing the substitution F211L, was found in two unrelated patients. A third mutation, resulting in the likely non-pathogenic substitution S289L, as well as a polymorphism not reported previously, was found in exon 3. CONCLUSIONS: The screening procedure described allows detection of mutations in all of the exons, including the polymorphic 5' and 3' ends of the gene, and is therefore suitable for routine screening of peripherin/RDS gene defects in patients with autosomal dominant retinitis pigmentosa. The frequency of mutations found in the Swedish patient group indicates that defects in the peripherin/RDS gene might be a more common cause of autosomal dominant retinitis pigmentosa than was thought previously.     

Detection of alterations in all three exons of the peripherin/RDS gene in Swedish patients with retinitis pigmentosa using an efficient DGGE system.

AIMS: To develop a sensitive mutation screening procedure suitable for routine analysis of the peripherin/RDS gene, and to estimate the nature and prevalence of peripherin/RDS gene mutations in Swedish patients with autosomal dominant retinitis pigmentosa. METHODS: To make the method as sensitive as possible, as many as eight segments, covering the three exons and the flanking intron sequences of the peripherin/RDS gene, were analysed by denaturing gradient gel electrophoresis. A group of 38 Swedish patients with a clinical diagnosis of autosomal dominant retinitis pigmentosa were screened for mutations in the peripherin/RDS gene. RESULTS: Three point mutations were found in four of the patients and five polymorphisms were defined. One mutation in exon 1, R172W, has been described previously in other ethnic groups as causing a macular degeneration. Another mutation, in exon 2 and causing the substitution F211L, was found in two unrelated patients. A third mutation, resulting in the likely non-pathogenic substitution S289L, as well as a polymorphism not reported previously, was found in exon 3. CONCLUSIONS: The screening procedure described allows detection of mutations in all of the exons, including the polymorphic 5' and 3' ends of the gene, and is therefore suitable for routine screening of peripherin/RDS gene defects in patients with autosomal dominant retinitis pigmentosa. The frequency of mutations found in the Swedish patient group indicates that defects in the peripherin/RDS gene might be a more common cause of autosomal dominant retinitis pigmentosa than was thought previously.     

What genetics tells us about the causes and mechanisms of Parkinson's disease

Parkinson's disease (PD) is a common motor disorder of mysterious etiology. It is due to the progressive degeneration of the dopaminergic neurons of the substantia nigra and is accompanied by the appearance of intraneuronal inclusions enriched in α-synuclein, the Lewy bodies. It is becoming increasingly clear that genetic factors contribute to its complex pathogenesis. Over the past decade, the genetic basis of rare PD forms with Mendelian inheritance, representing no more than 10% of the cases, has been investigated. More than 16 loci and 11 associated genes have been identified so far; genome-wide association studies have provided convincing evidence that polymorphic variants in these genes contribute to sporadic PD. The knowledge acquired of the functions of their protein products has revealed pathways of neurodegeneration that may be shared between inherited and sporadic PD. An impressive set of data in different model systems strongly suggest that mitochondrial dysfunction plays a central role in clinically similar, early-onset autosomal recessive PD forms caused by parkin and PINK1, and possibly DJ-1 gene mutations. In contrast, α-synuclein accumulation in Lewy bodies defines a spectrum of disorders ranging from typical late-onset PD to PD dementia and including sporadic and autosomal dominant PD forms due to mutations in SCNA and LRRK2. However, the pathological role of Lewy bodies remains uncertain, as they may or may not be present in PD forms with one and the same LRRK2 mutation. Impairment of autophagy-based protein/organelle degradation pathways is emerging as a possible unifying but still fragile pathogenic scenario in PD. Strengthening these discoveries and finding other convergence points by identifying new genes responsible for Mendelian forms of PD and exploring their functions and relationships are the main challenges of the next decade. It is also the way to follow to open new promising avenues of neuroprotective treatment for this devastating disorder.     

Analysis of the PINK1 gene in a cohort of patients with sporadic early-onset parkinsonism in Taiwan

Mutations in the PINK1 gene have been shown to cause autosomal recessive Parkinson's disease (PD) and/or early onset sporadic PD in Italy, Spain, North America, Ireland, and Asia. However, there are limited data on PINK1 mutations in sporadic early onset Asian PD patients. To determine the prevalence of PINK1 mutation in Taiwanese population, we conducted genetic analysis of PINK1 mutation in 73 early onset sporadic PD and 94 normal control subjects. We only identified a novel single heterozygous mutation R 407Q mutation in exon 6 of this gene in one patient at the age onset of 54. Overall, these data indicate that PINK1 mutations are rare in our population. Based on our results, unless common mutational hotspots are identified, routine testing for this mutation at least in our population may not be cost-effective.     

Imaging the impact of genes on Parkinson's disease

Although Parkinson's disease (PD) has traditionally been considered to be a non-genetic disorder, recent progress in the neurogenetics of PD provided converging evidence that genetic factors play a relevant role in the etiology of PD. The strongest case for a genetic contribution to PD was made by the discovery of mutations in single genes that can cause autosomal dominant (α-synuclein (SNCA)) and leucine rich repeat kinase 2 (LRRK2) gene) or recessive (Parkin, PTEN-induced putative kinase 1 (PINK1), DJ-1, and ATP13A2 gene) forms of PD. Here, we review how structural and functional neuroimaging of individuals carrying a mutation in one of the PD genes has offered a unique avenue of research into the pathogenesis of PD. In symptomatic mutation carriers (i.e. those with overt disease), brain mapping can help to link the molecular pathogenesis of PD more directly with functional and structural changes in the intact human brain. In addition, neuroimaging of presymptomatic (i.e. non-manifesting) mutation carriers has emerged as a valuable tool to identify mechanisms of adaptive motor reorganization at the preclinical stage that may prevent or delay clinical manifestation. In addition to mutations causing monogenic forms of PD, common polymorphisms in genes that influence mono-aminergic signaling or synaptic plasticity may have modifying effects on distinct aspects of PD. We also discuss how functional and structural neuroimaging can be used to better characterize these genotype-phenotype correlations.     

Genetic analysis of DJ-1 in a cohort Parkinson's disease patients of different ethnicity

Mutations in the DJ-1 gene have been described in autosomal recessive Parkinson's disease patients (ARPD) of European ancestry and young onset (YOPD) Ashkenazi Jewish and Afro-Caribbean patients. There is little information on the prevalence of DJ-1 mutations amongst Asian PD populations. In this study, we examined for DJ-1 mutations in consecutive YOPD and ARPD in a multi-ethnic cohort (Chinese, Malays, and Indians) of PD patients in a tertiary referral center. Sequence analysis of all the exons and the exon and intron boundaries of the DJ-1 gene were carried out. We did not find any DJ-1 mutations in these patients. A number of intronic variants with genotype frequency ranging from 15 to 90% were detected. Unlike Parkin, pathogenic DJ-1 mutations appear to be restricted to certain populations and are unlikely to be of clinical importance in our Asian cohort.     

Impaired dopamine storage resulting from alpha-synuclein mutations may contribute to the pathogenesis of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by the inability to initiate, execute and control movement. Neuropathologically, there is a striking loss of dopamine-producing neurons in the substantia nigra pars compacta, accompanied by depletion of dopamine in the striatum. Most forms of PD are sporadic, though in some cases familial inheritance is observed. In the late 1990s, two mutations in the alpha-synuclein gene were linked to rare, autosomal dominant forms of PD. Previously cloned from cholinergic vesicles of the Torpedo electric ray, alpha-synuclein is highly enriched in presynaptic nerve terminals and appears to be involved in synapse maintenance and plasticity. It is expressed ubiquitously in the brain, raising the important question of why dopaminergic neurons are primarily targeted in persons carrying mutations in alpha-synuclein. In this article, we review the current literature on alpha-synuclein and suggest a possible role for this protein in vesicle recycling via its regulation of phospholipase D2, its fatty acid-binding properties, or both. Exogenous application of dopamine, as well as redistribution of vesicular dopamine to the cytoplasm, can be toxic to dopaminergic neurons. Thus, impaired neurotransmitter storage arising from mutations in alpha-synuclein could lead to cytoplasmic accumulation of dopamine. The breakdown of this labile neurotransmitter in the cytoplasm could, in turn, promote oxidative stress and metabolic dysfunction, both of which have been observed in nigral tissue from PD patients.