Assessment of PINK1 (PARK6) polymorphisms in Finnish PD

Recent data has demonstrated that mutations in PINK1, encoding PTEN-induced kinase 1, are a cause of early onset recessive parkinsonism (PARK6 locus). Common variability in genes implicated in hereditary forms of parkinsonism may be a predisposing factor in sporadic Parkinson's disease (PD). We analyzed whether six different genetic variants within and surrounding PINK1 contribute to the risk of sporadic PD in a Finnish case-control series. Our results indicate that this gene does not play a major role in the genetic predisposition to PD in this population.     

Whole gene deletion and splicing mutations expand the PINK1 genotypic spectrum

Autosomal recessive parkinsonism is a genetic condition closely resembling Parkinson disease, the only distinguishing features being an earlier age at onset and a slower disease progression. Three causative genes have been identified so far. While exon rearrangements are frequently encountered in the Parkin gene, most PINK1 mutations are represented by single nucleotide changes. We report a sporadic parkinsonian patient carrying a deletion of the entire PINK1 gene and a splice site mutation (g.15445_15467del23) which produces several aberrant mRNAs. This report expands the genotypic spectrum of PINK1 mutations, with relevant implications for molecular analysis of this gene.     

A common A340T variant in PINK1 gene associated with late-onset Parkinson's disease in Chinese

Parkinson's disease (PD) is a complex neurodegenerative disease with genetic risk factors. Common variants in genes implicated in hereditary forms of parkinsonism may be predisposing factors for sporadic PD. Recent studies have demonstrated that mutations in PINK1 (PARK6 locus) gene, encoding PTEN-induced kinase 1, are associated with both familial recessive and sporadic early onset parkinsonism. In order to assess whether the coding variant A340T contributes to the risk of late-onset PD, we performed an association study of 539 PD patients with an onset age at or older than 50 and 525 controls in Chinese Han. Genotyping was performed by denaturing high performance liquid chromatography (DHPLC) combined with sequencing analyses. The A-allele frequency was 6.2% in PD and 4.2% in controls (p=0.0404), while G/A genotype frequencies were 12.4% in PD and 8.4% in the controls (p=0.0350). Our results yielded significant evidence for disease association between PINK1 A340T and PD with later onset (OR 1.55, 95% CI 1.04-2.32, p=0.0393), thus suggesting that PINK1 A340T variant may contribute to the risk for late-onset PD in Chinese.     

Genetic association study of PINK1 coding polymorphisms in Parkinson's disease

Parkinson's disease (PD) is the most common neurodegenerative movement disorder with a substantial genetic component (which is more pronounced in earlier onset cases). In addition to three well-confirmed PD genes (SNCA, parkin and DJ-1), mutations in the PTEN Induced Kinase (PINK1) gene have recently been identified in families with recessive early onset PD. We tested the hypothesis that three common coding variations (Leu63Leu, Ala340Thr and Asn521Thr) could increase the risk of PD. We performed a case control association study in a series of 91 PD cases (Caucasian of Canadian origin) and 182 normal controls. The patients were largely pre-selected for having an early age of onset (<50 years) and/or a positive family history. Our results did not reveal any evidence of association between PD and any of the three SNPs at the allelic or genotypic levels (p > 0.25). Furthermore, we did not detect a modifying effect for any genotype upon the age of onset in the PD group (p > 0.19). Nevertheless, it remains to be evaluated whether PINK1 variations contribute to the risk of common late onset sporadic PD.     

Mutation analysis of the parkin and PINK1 genes in American Caucasian early-onset Parkinson disease families

Mutations in the parkin gene and the PTEN-induced putative kinase 1 gene (PINK1) have been identified as the most common causes of autosomal recessive early-onset Parkinson disease (EOPD). To investigate the presence of the parkin and PINK1 gene mutation(s) and to explore genotype-phenotype correlations in American Caucasian families with EOPD from North American, we screened these two genes in probands of six families by direct sequencing, semi-quantitative PCR and RT-PCR. No PINK1 gene mutation was found in any of the probands, but compound heterozygous mutations (EX 3 del and EX 3_4 del) in the parkin gene were identified in one family. Extended analysis of the parkin-positive family showed the phenotype of patients was that of classic autosomal recessive EOPD, characterized by early age at onset, slow progression, beneficial response to levodopa, and levodopa-related motor complications. Three heterozygous mutation carriers (EX 3 del or EX 3_4 del) were free of any neurological symptoms. None of 62 healthy controls harbored EX 3 del or EX 3_4 del mutation. Our data suggest that compound heterozygous mutations (EX 3 and EX 3_4 del) in the parkin gene were the cause of EOPD in one of six Caucasian families; heterozygous EX 3 del and heterozygous EX 3_4 del forms were insufficient to cause this disorder, consistent with a loss-of-function mechanism of the parkin mutations. The results may provide new insights into the cause and diagnosis of PD and have implications for genetic counseling.     

Parkinson disease: insights in clinical, genetic and pathological features of monogenic disease subtypes

In the past 15 years, insights in clinical and genetic characteristics of Parkinson disease (PD) have increased substantially. Sequence or copy number variants in at least six genes (SNCA, LRRK2, PARK2, PINK1, DJ-1 and ATP13A2) have been identified to cause monogenic forms of PD. Routine clinical testing for mutations in these genes is feasible and available, but overlapping phenotypes in monogenic and sporadic PD complicate straightforward diagnostic screening. Primarily, a positive familial history and an early onset age should prompt clinicians to consider genetic testing. Based on a literature review on clinical and neuropathological features of PD patients carrying a pathogenic mutation we propose guidelines for genetic diagnostic testing in clinical practice. However, the absence of disease-modifying therapies and the variable penetrance of most known mutations currently limit the usefulness of genetic diagnostic testing for PD in clinical practice.     

Analysis of the regulatory and catalytic domains of PTEN-induced kinase-1 (PINK1)

Mutations of the phosphatase and tensin homolog (PTEN)‐induced kinase 1 (PINK1) gene can cause early‐onset familial Parkinson disease (PD). PINK1 encodes a neuroprotective protein kinase localized at the mitochondria, and its involvement in regulating mitochondrial dynamics, trafficking, structure, and function is well documented. Owing to the lack of information on structure and biochemical properties for PINK1, exactly how PINK1 exerts its neuroprotective function and how the PD‐causative mutations impact on PINK1 structure and function remain unclear. As an approach to address these questions, we conducted bioinformatic analyses of the mitochondrial targeting, the transmembrane, and kinase domains of PINK1 to predict the motifs governing its regulation and function. Our report sheds light on how PINK1 is targeted to the mitochondria and how PINK1 is cleaved by mitochondrial peptidases. Moreover, it includes a potential optimal phosphorylation sequence preferred by the PINK1 kinase domain. On the basis of the results of our analyses, we predict how the PD‐causative mutations affect processing of PINK1 in the mitochondria, PINK1 kinase activity, and substrate specificity. In summary, our results provide a conceptual framework for future investigation of the structural and biochemical basis of regulation and the neuroprotective mechanism of PINK1. Hum Mutat 33:1408–1422, 2012. © 2012 Wiley Periodicals, Inc.     

PINK1, Parkin, and DJ-1 mutations in Italian patients with early-onset parkinsonism

Recessively inherited early-onset parkinsonism (EOP) has been associated with mutations in the Parkin, DJ-1, and PINK1 genes. We studied the prevalence of mutations in all three genes in 65 Italian patients (mean age of onset: 43.2+/-5.4 years, 62 sporadic, three familial), selected by age at onset equal or younger than 51 years. Clinical features were compatible with idiopathic Parkinson's disease in all cases. To detect small sequence alterations in Parkin, DJ-1, and PINK1, we performed a conventional mutational analysis (SSCP/dHPLC/sequencing) of all coding exons of these genes. To test for the presence of exon rearrangements in PINK1, we established a new quantitative duplex PCR assay. Gene dosage alterations in Parkin and DJ-1 were excluded using previously reported protocols. Five patients (8%; one woman/four men; mean age at onset: 38.2+/-9.7 (range 25-49) years) carried mutations in one of the genes studied: three cases had novel PINK1 mutations, one of which occurred twice (homozygous c.1602_1603insCAA; heterozygous c.1602_1603insCAA; heterozygous c.836G>A), and two patients had known Parkin mutations (heterozygous c.734A>T and c.924C>T; heterozygous c.924C>T). Family history was negative for all mutation carriers, but one with a history of tremor. Additionally, we detected one novel polymorphism (c.344A>T) and four novel PINK1 changes of unknown pathogenic significance (-21G/A; IVS1+97A/G; IVS3+38_40delTTT; c.852C>T), but no exon rearrangements. No mutations were found in the DJ-1 gene. The number of mutation carriers in both the Parkin and the PINK1 gene in our cohort is low but comparable, suggesting that PINK1 has to be considered in EOP.     

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.     

Relative contribution of simple mutations vs. copy number variations in five Parkinson disease genes in the Belgian population

The relative contribution of simple mutations and copy number variations (CNVs) in SNCA, PARK2, PINK1, PARK7, and LRRK2 to the genetic etiology of Parkinson disease (PD) is still unclear because most studies did not completely analyze each gene. In a large group of Belgian PD patients (N=310) and control individuals (N=270), we determined the mutation frequency of both simple mutations and CNVs in these five PD genes, using direct sequencing, multiplex amplicon quantification (MAQ), and real‐time PCR assays. Overall, we identified 14 novel heterozygous variants, of which 11 were absent in control individuals. We observed eight PARK2 (multiple) exon multiplications in PD patients and one exon deletion in a control individual. Furthermore, we identified one SNCA whole‐gene duplication. The PARK2 and LRRK2 mutation frequencies in Belgian PD patients were similar to those reported in other studies. However, at this stage the true pathogenic nature of some heterozygous mutations in recessive genes remains elusive. Furthermore, though mutations is SNCA, PINK1, and PARK7 are rare, our identification of a SNCA duplication confirmed that screening of these genes remains meaningful. Hum Mutat 30:1–8, 2009. © 2009 Wiley‐Liss, Inc.     

Mutation analysis of the BRCA1 and BRCA2 genes in the Belgian patient population and identification of a Belgian founder mutation BRCA1 IVS5 + 3A > G

Since the identification of the BRCA1 and BRCA2 genes, several hundred different germline mutations in both genes have been reported. Recurrent mutations are rare and mainly due to founder effects. As the mutational spectrum of the BRCA1 and BRCA2 genes in the Belgian patient population is largely unknown, we initiated mutation analysis for the complete coding sequence of both genes in Belgian families with multiple breast and/or ovarian cancer patients and in "sporadic" patients with early onset disease. We completed the analysis in 49 families and in 19 "sporadic" female patients with early onset breast and/or ovarian cancer. In 15 families we identified a mutation (12 mutations in BRCA1 and 3 mutations in BRCA2). In 5 apparently unrelated families the same splice site mutation was identified (BRCA1 IVS5 + 3A > G). Haplotype analysis revealed a common haplotype immediately flanking the mutation in all families suggesting that disease alleles are identical by descent. In none of the 19 sporadic patients was a mutation found.     

PINK1 heterozygous rare variants: prevalence, significance and phenotypic spectrum

Heterozygous rare variants in the PINK1 gene, as well as in other genes causing autosomal recessive parkinsonism, have been reported both in patients and healthy controls. Their pathogenic significance is uncertain, but they have been suggested to represent risk factors to develop Parkinson disease (PD). The few large studies that assessed the frequency of PINK1 heterozygotes in cases and controls yielded controversial results, and the phenotypic spectrum is largely unknown. We retrospectively analyzed the occurrence of PINK1 heterozygous rare variants in over 1100 sporadic and familial patients of all onset ages and in 400 controls. Twenty patients and 6 controls were heterozygous, with frequencies (1.8% vs. 1.5%) not significantly different in the two groups. Clinical features of heterozygotes were indistinguishable to those of wild-type patients, with mean disease onset 10 years later than in carriers of two mutations but worse disease progression. A meta-analysis indicated that, in PINK1 heterozygotes, the PD risk is only slightly increased with a non significant odds ratio of 1.62. These findings suggest that PINK1 heterozygous rare variants play only a minor susceptibility role in the context of a multifactorial model of PD. Hence, their significance should be kept distinct from that of homozygous/compound heterozygous mutations, that cause parkinsonism inherited in a mendelian fashion.     

Mutation analysis of parkin and PINK1 genes in early-onset Parkinson's disease in China

A series of 69 Han Chinese PD patients (including 66 index cases and 3 relatives) with early-onset Parkinson's disease (EOPD) were studied to assess the frequency of parkin and PINK1 gene mutations. Mutation analysis of the parkin gene was performed by real-time quantitative polymerase chain reaction (QPCR), denaturing high-performance liquid chromatography (DHPLC) and DNA sequencing. For the PINK1 gene, DHPLC and DNA sequencing were used. Nineteen patients (including one relative) had mutation in the parkin gene, and the c.2T > C (p.M1T) was not reported previously. No mutation of the PINK1 gene was found. The onset age of the patients with mutations in the parkin was earlier than that of those without mutation (p < 0.05). We concluded that mutations in parkin gene are common in Chinese EOPD patients, and mainly are exon rearrangements, while mutation in PINK1 might be not common in Chinese EOPD 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.     

A study of LRRK2 mutations and Parkinson's disease in Brazil

Mutations in the Leucine-rich repeat kinase 2 (LRRK2) gene are known as a common cause of Parkinson's disease (PD) among patients from different geographic origins. In this study, we evaluated the prevalence of LRRK2 mutations in exons 31 and 41 in a cohort of 154 consecutive, unrelated Brazilian patients with familial or sporadic PD, including early and late onset patients. The LRRK2 p.G2019S mutation was present in heterozygous state in three index cases (approximately 2%), and in three additional relatives. No carriers of this mutation were found among 250 control chromosomes. Clinically, all mutation-positive patients presented a typical PD phenotype and a good response to levodopa. Mutation segregation analysis in a large sibling showed incomplete penetrance of the p.G2019S. Our findings suggest that the LRRK2 p.G2019S mutation has a substantial contribution to PD susceptibility among Brazilian population and add new clues to current research of this disease.     

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.     

VPS35 Asp620Asn and EIF4G1 Arg1205His mutations are rare in Parkinson disease from Southwest China

The Asp620Asn mutation in the vacuolar protein sorting protein 35 (VPS35) gene and the Arg1205His mutation in the eukaryotic translation initiation factor 4 gamma 1 (EIF4G1) gene were identified in autosomal dominant late-onset familial and sporadic Parkinson disease (PD) patients in a Caucasian population. However, the frequencies of these 2 mutations among Chinese PD patients are unknown. We examined these mutations in a large cohort consisting of 609 PD patients and 600 healthy control subjects from Southwest China. Our results suggest that the Asp620Asn mutation in VPS35 and the Arg1205His mutation in EIF4G1 do not play a role in PD in the Southwest China population. The novel Arg1205Cys mutation in EIF4G1 detected in the current study should be further studied among other Asian patients.     

Genetic analysis of SCA2, 3 and 17 in idiopathic Parkinson's disease

Recent reports of SCA2 and SCA3 patients who presented with levodopa responsive parkinsonism have generated considerable interest as they have implications for genetic testing. It is unclear whether ethnic race alone or founder effects within certain geographical region explain such an association. In this study, we conducted genetic analysis of SCA2, 3, 17 in an ethnic Chinese cohort with early onset and familial Parkinson's disease (PD) and healthy controls. A total of 191 subjects comprising of 91 PD and 100 healthy controls were examined. We identified one positive case of SCA2 in an early-onset sporadic PD patient who had CAG 36 repeats, yielding a prevalence of 2.2% in early-onset sporadic PD patients and less than 1.0% in our study PD population. The size of the repeats was lower than the expanded repeats (38-57) in SCA2 patients with ataxia in our population. All the children of the patient were physically normal even though some of them carried the repeat expansion of similar size. No cases and controls were positive for SCA3 and SCA17. We do not think routine screening of SCA2, SCA3 and SCA17 for all idiopathic PD patients is cost-effective in our ethnic Chinese population. However, SCA2 should be a differential diagnosis in young onset sporadic PD when genetic mutations of other known PD genes have been excluded.     

中国乳腺癌患者BRCA1基因的频发突变5589del8

目的研究在中国大陆乳腺癌人群中是否存在BRCAI／2基因突变的“热点”。方法研究对象为来自全国4个乳腺癌医疗中心的177例家族性和早发性乳腺癌患者和426例散发性乳腺癌患者,根据前期研究中已发现的BRCAI／2基因突变位点,应用变性高效液相色谱分析和DNA测序技术对这些患者进行已知位点的突变检测。结果在前期研究的70例家族性和早发性乳腺癌患者和本研究的177例患者（共247例）中,共发现3例BRCAl5589del8突变的携带者,在426例散发性乳腺癌患者中也发现了2例BRCAl5589del8突变的携带者。单倍型分析的结果显示这5例患者具有相近甚至相同的单倍型。结论BRCAl5589del8突变是中国人群中BRCAl基因的频发突变,它是否是中国人群中的“始祖突变”仍需进一步研究证实。     

Pathogenic mutations in Parkinson disease

Parkinson disease (PD; Parkinson's) is the second most common neurodegenerative disease, characterized by the progressive loss of dopamine neurons and the accumulation of Lewy bodies. Increasing evidence suggests that deficits in mitochondrial function, oxidative and nitrosative stress, the accumulation of aberrant or misfolded proteins, and ubiquitin-proteasome system (UPS) dysfunction may represent the principal molecular pathways that commonly underlie the pathogenesis. The relative role of genetic and environmental factors has been the focus of research and debate. The recent discovery of a number of disease-causing genes (SNCA, Parkin/PARK2, UCHL1, PINK1, DJ1/PARK7, and LRRK2) in familial and sporadic forms of PD has provided considerable insights into the pathophysiology of this complex disorder. The frequency of these gene mutations may vary according to ethnicity and to the specific gene. A gene dosage effect is observed in some cases, and the phenotype of some of the mutation carriers closely resembles typical PD. Penetrance of some of the recurrent mutations is incomplete and may vary with age. Further research to unravel the etiopathology could identify biochemical or genetic markers for potential neuroprotective trials.