Novel mutations, pseudo-dominant inheritance, and possible familial affects in patients with autosomal recessive juvenile parkinsonism

Genetic Variations and Neuropathologic Features of Patients with PRKN Mutations

BACKGROUND

Mutations in PRKN are the most common cause of autosomal recessive juvenile parkinsonism. The objective of this study was to investigate the association between genotype and pathology in patients with PRKN mutations.

METHODS

We performed a sequence and copy number variation analysis of PRKN, mRNA transcripts, Parkin protein expression, and neuropathology in 8 autopsied patients.

RESULTS

All the patients harbored biallelic PRKN mutations. Two patients were homozygous and heterozygous, respectively, for the missense mutation p.C431F. Seven patients had exon rearrangements, including 2 patients from a single family who harbored a homozygous deletion of exon 4, and 3 patients who carried a homozygous duplication of exons 6-7, a homozygous duplication of exons 10-11, and a heterozygous duplication of exons 2-4. In the other 2 patients, we found a compound heterozygous duplication of exon 2, deletion of exon 3, and a heterozygous duplication of exon 2. However, sequencing of cDNA prepared from mRNA revealed 2 different transcripts derived from triplication of exon 2 and deletion of exons 2-3 and from duplication of exons 2-4 and deletion of exons 3-4. Western blotting and immunohistochemistry revealed faint or no expression of Parkin in their brains. In the substantia nigra pars compacta, a subfield-specific pattern of neuronal loss and mild gliosis were evident. Lewy bodies were found in 3 patients. Peripheral sensory neuronopathy was a feature.

CONCLUSIONS

Genomic and mRNA analysis is needed to identify the PRKN mutations. Variable mutations may result in no or little production of mature Parkin and the histopathologic features may be similar. © 2021 International Parkinson and Movement Disorder Society.

Mechanisms of PINK1, ubiquitin and Parkin interactions in mitochondrial quality control and beyond

Parkinson's disease (PD) is a degenerative movement disorder resulting from the loss of specific neuron types in the midbrain. Early environmental and pathophysiological studies implicated mitochondrial damage and protein aggregation as the main causes of PD. These findings are now vindicated by the characterization of more than 20 genes implicated in rare familial forms of the disease. In particular, two proteins encoded by the Parkin and PINK1 genes, whose mutations cause early-onset autosomal recessive PD, function together in a mitochondrial quality control pathway. In this review, we will describe recent development in our understanding of their mechanisms of action, structure, and function. We explain how PINK1 acts as a mitochondrial damage sensor via the regulated proteolysis of its N-terminus and the phosphorylation of ubiquitin tethered to outer mitochondrial membrane proteins. In turn, phospho-ubiquitin recruits and activates Parkin via conformational changes that increase its ubiquitin ligase activity. We then describe how the formation of polyubiquitin chains on mitochondria triggers the recruitment of the autophagy machinery or the formation of mitochondria-derived vesicles. Finally, we discuss the evidence for the involvement of these mechanisms in physiological processes such as immunity and inflammation, as well as the links to other PD genes.

Phosphorylation of Parkin at serine 65 is essential for its activation in vivo

Mutations in PINK1 and Parkin result in autosomal recessive Parkinson's disease (PD). Cell culture and in vitro studies have elaborated the PINK1-dependent regulation of Parkin and defined how this dyad orchestrates the elimination of damaged mitochondria via mitophagy. PINK1 phosphorylates ubiquitin at serine 65 (Ser65) and Parkin at an equivalent Ser65 residue located within its N-terminal ubiquitin-like domain, resulting in activation; however, the physiological significance of Parkin Ser65 phosphorylation in vivo in mammals remains unknown. To address this, we generated a Parkin Ser65Ala (S65A) knock-in mouse model. We observe endogenous Parkin Ser65 phosphorylation and activation in mature primary neurons following mitochondrial depolarization and reveal this is disrupted in Parkin ^S65A/S65A neurons. Phenotypically, Parkin ^S65A/S65A mice exhibit selective motor dysfunction in the absence of any overt neurodegeneration or alterations in nigrostriatal mitophagy. The clinical relevance of our findings is substantiated by the discovery of homozygous PARKIN (PARK2) p.S65N mutations in two unrelated patients with PD. Moreover, biochemical and structural analysis demonstrates that the Parkin^S65N/S65N mutant is pathogenic and cannot be activated by PINK1. Our findings highlight the central role of Parkin Ser65 phosphorylation in health and disease.

Twenty years since the discovery of the parkin gene

Nearly 20 years have passed since we identified the causative gene for a familial Parkinson's disease, parkin (now known as PARK2), in 1998. PARK2 is the most common gene responsible for young-onset Parkinson's disease. It codes for the protein Parkin RBR E3 ubiquitin-protein ligase (PARK2), which directly links to the ubiquitin-proteasome as a ubiquitin ligase. PARK2 is involved in mitophagy, which is a type of autophagy, in collaboration with PTEN-induced putative kinase 1 (PINK1). The PINK1 gene (previously known as PARK6) is also a causative gene for young-onset Parkinson's disease. Both gene products may be involved in regulating quality control within the mitochondria. The discovery of PARK2 as a cause of young-onset Parkinson's disease has had a major impact on other neurodegenerative diseases. The involvement of protein degradation systems has been implicated as a common mechanism for neurodegenerative diseases in which inclusion body formation is observed. The discovery of the involvement of PARK2 in Parkinson's disease focused attention on the involvement of protein degradation systems in neurodegenerative diseases. In this review, we focus on the history of the discovery of PARK2, the clinical phenotypes of patients with PARK2 mutations, and its functional roles.

PINK1, Parkin, and Mitochondrial Quality Control: What can we Learn about Parkinson's Disease Pathobiology?

The first clinical description of Parkinson's disease (PD) will embrace its two century anniversary in 2017. For the past 30 years, mitochondrial dysfunction has been hypothesized to play a central role in the pathobiology of this devastating neurodegenerative disease. The identifications of mutations in genes encoding PINK1 (PTEN-induced kinase 1) and Parkin (E3 ubiquitin ligase) in familial PD and their functional association with mitochondrial quality control provided further support to this hypothesis. Recent research focused mainly on their key involvement in the clearance of damaged mitochondria, a process known as mitophagy. It has become evident that there are many other aspects of this complex regulated, multifaceted pathway that provides neuroprotection. As such, numerous additional factors that impact PINK1/Parkin have already been identified including genes involved in other forms of PD. A great pathogenic overlap amongst different forms of familial, environmental and even sporadic disease is emerging that potentially converges at the level of mitochondrial quality control. Tremendous efforts now seek to further detail the roles and exploit PINK1 and Parkin, their upstream regulators and downstream signaling pathways for future translation. This review summarizes the latest findings on PINK1/Parkin-directed mitochondrial quality control, its integration and cross-talk with other disease factors and pathways as well as the implications for idiopathic PD. In addition, we highlight novel avenues for the development of biomarkers and disease-modifying therapies that are based on a detailed understanding of the PINK1/Parkin pathway.

A novel missense mutation of CMT2P alters transcription machinery

OBJECTIVE

Charcot-Marie-Tooth type 2P (CMT2P) has been associated with frameshift mutations in the RING domain of LRSAM1 (an E3 ligase). This study describes families with a novel missense mutation of LRSAM1 gene and explores pathogenic mechanisms of CMT2P.

METHODS

Patients with CMT2P were characterized clinically, electrophysiologically, and genetically. A neuronal model with the LRSAM1 mutation was created using CRISPR/Cas9 technology. The neuronal cell line along with fibroblasts isolated from the patients was used to study RNA-binding proteins.

RESULTS

This American family with dominantly inherited axonal polyneuropathy reveals a phenotype similar to those in previously reported non-US families. The affected members in our family cosegregated with a novel missense mutation Cys694Arg that alters a highly conserved cysteine in the RING domain. This mutation leads to axonal degeneration in the in vitro neuronal cell line. Moreover, using protein mass spectrometry, we identified a group of RNA-binding proteins (including FUS, a protein critically involved in motor neuron degeneration) that interacted with LRSAM1. The interactions were disrupted by the Cys694Arg mutation, which resulted in reduction of intranuclear RNA-binding proteins.

INTERPRETATION

Our findings suggest that the mutant LRSAM1 may aberrantly affect the formation of transcription machinery. Given that a similar mechanism has been reported in motor neuron degeneration of amyotrophic lateral sclerosis, abnormalities of RNA/RNA-binding protein complex may play a role in the neuronal degeneration of CMT2P. Ann Neurol 2016;80:834-845.

Neural stem cells in Parkinson's disease: a role for neurogenesis defects in onset and progression

Parkinson's disease (PD) is the second most common neurodegenerative disorder, leading to a variety of motor and non-motor symptoms. Interestingly, non-motor symptoms often appear a decade or more before the first signs of motor symptoms. Some of these non-motor symptoms are remarkably similar to those observed in cases of impaired neurogenesis and several PD-related genes have been shown to play a role in embryonic or adult neurogenesis. Indeed, animal models deficient in Nurr1, Pitx3, SNCA and PINK1 display deregulated embryonic neurogenesis and LRRK2 and VPS35 have been implicated in neuronal development-related processes such as Wnt/β-catenin signaling and neurite outgrowth. Moreover, adult neurogenesis is affected in both PD patients and PD animal models and is regulated by dopamine and dopaminergic (DA) receptors, by chronic neuroinflammation, such as that observed in PD, and by differential expression of wild-type or mutant forms of PD-related genes. Indeed, an increasing number of in vivo studies demonstrate a role for SNCA and LRRK2 in adult neurogenesis and in the generation and maintenance of DA neurons. Finally, the roles of PD-related genes, SNCA, LRRK2, VPS35, Parkin, PINK1 and DJ-1 have been studied in NSCs, progenitor cells and induced pluripotent stem cells, demonstrating a role for some of these genes in stem/progenitor cell proliferation and maintenance. Together, these studies strongly suggest a link between deregulated neurogenesis and the onset and progression of PD and present strong evidence that, in addition to a neurodegenerative disorder, PD can also be regarded as a developmental disorder.

Alternative splicing generates different parkin protein isoforms: evidences in human, rat, and mouse brain

Parkinson protein 2, E3 ubiquitin protein ligase (PARK2) gene mutations are the most frequent causes of autosomal recessive early onset Parkinson's disease and juvenile Parkinson disease. Parkin deficiency has also been linked to other human pathologies, for example, sporadic Parkinson disease, Alzheimer disease, autism, and cancer. PARK2 primary transcript undergoes an extensive alternative splicing, which enhances transcriptomic diversification. To date several PARK2 splice variants have been identified; however, the expression and distribution of parkin isoforms have not been deeply investigated yet. Here, the currently known PARK2 gene transcripts and relative predicted encoded proteins in human, rat, and mouse are reviewed. By analyzing the literature, we highlight the existing data showing the presence of multiple parkin isoforms in the brain. Their expression emerges from conflicting results regarding the electrophoretic mobility of the protein, but it is also assumed from discrepant observations on the cellular and tissue distribution of parkin. Although the characterization of each predicted isoforms is complex, since they often diverge only for few amino acids, analysis of their expression patterns in the brain might account for the different pathogenetic effects linked to PARK2 gene mutations.

Reprint of: revisiting oxidative stress and mitochondrial dysfunction in the pathogenesis of Parkinson disease-resemblance to the effect of amphetamine drugs of abuse

Parkinson disease (PD) is a chronic and progressive neurological disease associated with a loss of dopaminergic neurons. In most cases the disease is sporadic but genetically inherited cases also exist. One of the major pathological features of PD is the presence of aggregates that localize in neuronal cytoplasm as Lewy bodies, mainly composed of α-synuclein (α-syn) and ubiquitin. The selective degeneration of dopaminergic neurons suggests that dopamine itself may contribute to the neurodegenerative process in PD. Furthermore, mitochondrial dysfunction and oxidative stress constitute key pathogenic events of this disorder. Thus, in this review we give an actual perspective to classical pathways involving these two mechanisms of neurodegeneration, including the role of dopamine in sporadic and familial PD, as well as in the case of abuse of amphetamine-type drugs. Mutations in genes related to familial PD causing autosomal dominant or recessive forms may also have crucial effects on mitochondrial morphology, function, and oxidative stress. Environmental factors, such as MPTP and rotenone, have been reported to induce selective degeneration of the nigrostriatal pathways leading to α-syn-positive inclusions, possibly by inhibiting mitochondrial complex I of the respiratory chain and subsequently increasing oxidative stress. Recently, increased risk for PD was found in amphetamine users. Amphetamine drugs have effects similar to those of other environmental factors for PD, because long-term exposure to these drugs leads to dopamine depletion. Moreover, amphetamine neurotoxicity involves α-syn aggregation, mitochondrial dysfunction, and oxidative stress. Therefore, dopamine and related oxidative stress, as well as mitochondrial dysfunction, seem to be common links between PD and amphetamine neurotoxicity.

Parkin mitochondrial translocation is achieved through a novel catalytic activity coupled mechanism

Pink1, a mitochondrial kinase, and Parkin, an E3 ubiquitin ligase, function in mitochondrial maintenance. Pink1 accumulates on depolarized mitochondria, where it recruits Parkin to mainly induce K63-linked chain ubiquitination of outer membrane proteins and eventually mitophagy. Parkin belongs to the RBR E3 ligase family. Recently, it has been proposed that the RBR domain transfers ubiquitin to targets via a cysteine∼ubiquitin enzyme intermediate, in a manner similar to HECT domain E3 ligases. However, direct evidence for a ubiquitin transfer mechanism and its importance for Parkin's in vivo function is still missing. Here, we report that Parkin E3 activity relies on cysteine-mediated ubiquitin transfer during mitophagy. Mutating the putative catalytic cysteine to serine (Parkin C431S) traps ubiquitin, and surprisingly, also abrogates Parkin mitochondrial translocation, indicating that E3 activity is essential for Parkin translocation. We found that Parkin can bind to K63-linked ubiquitin chains, and that targeting K63-mimicking ubiquitin chains to mitochondria restores Parkin C431S localization. We propose that Parkin translocation is achieved through a novel catalytic activity coupled mechanism.

Accumulation of the parkin substrate, FAF1, plays a key role in the dopaminergic neurodegeneration

This study reports the physical and functional interplay between Fas-associated factor 1 (FAF1), a death-promoting protein, and parkin, a key susceptibility protein for Parkinson's disease (PD). We found that parkin acts as an E3 ubiquitin ligase to ubiquitinate FAF1 both in vitro and at cellular level, identifying FAF1 as a direct substrate of parkin. The loss of parkin function due to PD-linked mutations was found to disrupt the ubiquitination and degradation of FAF1, resulting in elevated FAF1 expression in SH-SY5Y cells. Moreover, FAF1-mediated cell death was abolished by wild-type parkin, but not by PD-linked parkin mutants, implying that parkin antagonizes the death potential of FAF1. This led us to investigate whether FAF1 participates in the pathogenesis of PD. To address this, we used a gene trap mutagenesis approach to generate mutant mice with diminished levels of FAF1 (Faf1(gt/gt)). Using the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mouse model of PD, we found that FAF1 accumulated in the substantia nigra pars compacta (SNc) of MPTP-treated PD mice, and that MPTP-induced dopaminergic cell loss in the SNc was significantly attenuated in Faf1(gt/gt) mice versus Faf1(+/+) mice. MPTP-induced reduction of locomotor activity was also lessened in Faf1(gt/gt) mice versus Faf1(+/+) mice. Furthermore, we found that FAF1 deficiency blocked PD-linked biochemical events, including caspase activation, ROS generation, JNK activation and cell death. Taken together, these results suggest a new role for FAF1: that of a positive modulator for PD.

Revisiting oxidative stress and mitochondrial dysfunction in the pathogenesis of Parkinson disease--resemblance to the effect of amphetamine drugs of abuse

Parkinson disease (PD) is a chronic and progressive neurological disease associated with a loss of dopaminergic neurons. In most cases the disease is sporadic but genetically inherited cases also exist. One of the major pathological features of PD is the presence of aggregates that localize in neuronal cytoplasm as Lewy bodies, mainly composed of α-synuclein (α-syn) and ubiquitin. The selective degeneration of dopaminergic neurons suggests that dopamine itself may contribute to the neurodegenerative process in PD. Furthermore, mitochondrial dysfunction and oxidative stress constitute key pathogenic events of this disorder. Thus, in this review we give an actual perspective to classical pathways involving these two mechanisms of neurodegeneration, including the role of dopamine in sporadic and familial PD, as well as in the case of abuse of amphetamine-type drugs. Mutations in genes related to familial PD causing autosomal dominant or recessive forms may also have crucial effects on mitochondrial morphology, function, and oxidative stress. Environmental factors, such as MPTP and rotenone, have been reported to induce selective degeneration of the nigrostriatal pathways leading to α-syn-positive inclusions, possibly by inhibiting mitochondrial complex I of the respiratory chain and subsequently increasing oxidative stress. Recently, increased risk for PD was found in amphetamine users. Amphetamine drugs have effects similar to those of other environmental factors for PD, because long-term exposure to these drugs leads to dopamine depletion. Moreover, amphetamine neurotoxicity involves α-syn aggregation, mitochondrial dysfunction, and oxidative stress. Therefore, dopamine and related oxidative stress, as well as mitochondrial dysfunction, seem to be common links between PD and amphetamine neurotoxicity.

Phenotypic variability of parkin mutations in single kindred

BACKGROUND

Mutations in parkin have been associated with autosomal recessive early-onset Parkinson's disease (PD). Here, we report on unusual phenotypic variability within a family with mutations in parkin.

METHODS

The proband and her parents were clinically assessed. Mutation analysis was performed using genomic DNA and complementary DNA. The protein expression of Parkin and Mitofusin 2 was examined by western blotting.

RESULTS

The proband was a compound heterozygote with no detectable Parkin and presented with early-onset PD. The father, a single heterozygote with reduced expression of Parkin, had mild loss of arm swing. The mother, who had only very mild rigidity, was unexpectedly found to be a homozygote with no Parkin expression. The proband, but not the parents, met the Queen Square Brain Bank criteria for PD. Parkin-dependent ubiquitination of Mitofusin 2 was impaired in the mother and the proband.

CONCLUSION

We report the first case of a homozygous mutation carrier in parkin who had no functional protein and only mild signs of parkinsonism in her seventh decade, whereas her daughter developed typical early-onset PD. This family demonstrates phenotypic variability in parkin-related parkinsonism. © 2012 Movement Disorder Society.

Following Ariadne's thread: a new perspective on RBR ubiquitin ligases

Ubiquitin signaling pathways rely on E3 ligases for effecting the final transfer of ubiquitin from E2 ubiquitin conjugating enzymes to a protein target. Here we re-evaluate the hybrid RING/HECT mechanism used by the E3 family RING-between-RINGs (RBRs) to transfer ubiquitin to substrates. We place RBRs into the context of current knowledge of HECT and RING E3s. Although not as abundant as the other types of E3s (there are only slightly more than a dozen RBR E3s in the human genome), RBRs are conserved in all eukaryotes and play important roles in biology. Re-evaluation of RBR ligases as RING/HECT E3s provokes new questions and challenges the field.

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.

Successful twin pregnancy in a patient with parkin-associated autosomal recessive juvenile parkinsonism

Background

Pregnancy in patients with Parkinson disease is a rare occurrence. To the best of our knowledge, the effect of pregnancy as well as treatment in genetically confirmed autosomal recessive juvenile parkinsonism (ARJP) has never been reported. Here, we report the first case of pregnancy in a patient with ARJP associated with a parkin gene mutation, ARJP/PARK2.

Case presentation

A 27-year-old woman with ARJP/PARK2 was diagnosed as having a spontaneous dichorionic/diamniotic twin pregnancy. Exacerbation of motor disability was noted between ovulation and menstruation before pregnancy as well as during late pregnancy, suggesting that her parkinsonism might have been influenced by fluctuations in the levels of endogenous sex hormones. During the organogenesis period, she was only treated with levodopa/carbidopa, although she continued to receive inpatient hospital care for assistance in the activities of daily living. After the organogenesis period, she was administered sufficient amounts of antiparkinsonian drugs. She delivered healthy male twins, and psychomotor development of both the babies was normal at the age of 2 years.

Conclusion

Pregnancy may worsen the symptoms of ARJP/PARK2, although appropriate treatments with antiparkinsonian drugs and adequate assistance in the activities of daily living might enable successful pregnancy and birth of healthy children.

UBCH7 reactivity profile reveals parkin and HHARI to be RING/HECT hybrids

Although the functional interaction between ubiquitin conjugating enzymes (E2s) and ubiquitin ligases (E3s) is essential in ubiquitin (Ub) signaling, the criteria that define an active E2–E3 pair are not well-established. The human E2 UbcH7 (Ube2L3) shows broad specificity for HECT-type E3s¹, but often fails to function with RING E3s in vitro despite forming specific complexes^2–4. Structural comparisons of inactive UbcH7/RING complexes with active UbcH5/RING complexes reveal no defining differences^3,4, highlighting a gap in our understanding of Ub transfer. We show that, unlike many E2s that transfer Ub with RINGs, UbcH7 lacks intrinsic, E3-independent reactivity with lysine, explaining its preference for HECTs. Despite lacking lysine reactivity, UbcH7 exhibits activity with the RING-In Between-RING (RBR) family of E3s that includes Parkin and human homologue of ariadne (HHARI)^5,6. Found in all eukaryotes⁷, RBRs regulate processes such as translation⁸ and immune signaling⁹. RBRs contain a canonical C3HC4-type RING, followed by two conserved Cys/His-rich Zn²⁺-binding domains, In-Between-RING (IBR) and RING2 domains, which together define this E3 family⁷. Here we show that RBRs function like RING/HECT hybrids: they bind E2s via a RING domain, but transfer Ub through an obligate thioester-linked Ub (denoted ‘~Ub’), requiring a conserved cysteine residue in RING2. Our results define the functional cadre of E3s for UbcH7, an E2 involved in cell proliferation¹⁰ and immune function¹¹, and suggest a novel mechanism for an entire class of E3s.

Parkin mono-ubiquitinates Bcl-2 and regulates autophagy

Parkin is an E3 ubiquitin ligase that mediates the ubiquitination of protein substrates. The mutations in the parkin gene can lead to a loss of function of parkin and cause autosomal recessive juvenile onset parkinsonism. Recently, parkin was reported to be involved in the regulation of mitophagy. Here, we identify the Bcl-2, an anti-apoptotic and autophagy inhibitory protein, as a substrate for parkin. Parkin directly binds to Bcl-2 via its C terminus and mediates the mono-ubiquitination of Bcl-2, which increases the steady-state levels of Bcl-2. Overexpression of parkin, but not its ligase-deficient forms, decreases autophagy marker LC3 conversion, whereas knockdown of parkin increases LC3 II levels. In HeLa cells, a parkin-deficient cell line, knockdown of parkin does not change LC3 conversion. Moreover, overexpression of parkin enhances the interactions between Bcl-2 and Beclin 1. Our results provide evidence that parkin mono-ubiquitinates Bcl-2 and regulates autophagy via Bcl-2.

Genetic etiology of Parkinson disease associated with mutations in the SNCA, PARK2, PINK1, PARK7, and LRRK2 genes: a mutation update

To date, molecular genetic analyses have identified over 500 distinct DNA variants in five disease genes associated with familial Parkinson disease; alpha-synuclein (SNCA), parkin (PARK2), PTEN-induced putative kinase 1 (PINK1), DJ-1 (PARK7), and Leucine-rich repeat kinase 2 (LRRK2). These genetic variants include approximately 82% simple mutations and approximately 18% copy number variations. Some mutation subtypes are likely underestimated because only few studies reported extensive mutation analyses of all five genes, by both exonic sequencing and dosage analyses. Here we present an update of all mutations published to date in the literature, systematically organized in a novel mutation database (http://www.molgen.ua.ac.be/PDmutDB). In addition, we address the biological relevance of putative pathogenic mutations. This review emphasizes the need for comprehensive genetic screening of Parkinson patients followed by an insightful study of the functional relevance of observed genetic variants. Moreover, while capturing existing data from the literature it became apparent that several of the five Parkinson genes were also contributing to the genetic etiology of other Lewy Body Diseases and Parkinson-plus syndromes, indicating that mutation screening is recommendable in these patient groups.

Identification and validation of control cell lines for accurate parkin dosage analysis

Mutation of the parkin gene (parkin) is the most common cause of early-onset Parkinson's disease and to date over 100 different mutations have been described. However, screening of parkin is complicated by its genomic architecture and context. Notably, dosage alterations in parkin account for greater than 50% of mutations detected in some cohort studies. To improve the accuracy and reproducibility of parkin genomic dosage assays we have identified and analysed cell lines with chromosomal abnormalities affecting 6q26. FISH and real-time PCR analysis identified cell lines with reduced or increased copy number spanning the entire parkin locus. These cell lines represent a valuable resource to facilitate accurate copy number determination of any parkin exon. The reagents are easily obtainable and are compatible with current quantitative technologies and platforms.

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.

Parkinsonism and essential tremor in a family with pseudo-dominant inheritance of PARK2: an FP-CIT SPECT study

We report a family with 5 affected individuals manifesting either essential tremor (ET), Parkinsonism, or both, consistent with pseudo-dominant inheritance of PARK2. Two homozygotes presented postural and kinetic tremor several years before the onset of Parkinsonism. Postural and kinetic tremor mimicking ET was the only feature in 1 homozygous and 2 heterozygous carriers of the mutation. Striatal dopamine transporter density was reduced in accordance with phenotype and number of mutated alleles. In 3 homozygotes and 1 heterozygote, a 2-year follow-up single photon emission computed tomography suggested no progression of nigrostriatal deficit.

Effective quantitative real-time polymerase chain reaction analysis of the parkin gene (PARK2) exon 1-12 dosage

Background

One of the causes of Parkinson's disease is mutations in the PARK2 gene. Deletions and duplications of single exons or exon groups account for a large proportion of the gene mutations. Direct detection of these mutations can be used for the diagnosis of Parkinson's disease.

Methods

To detect these mutations, we developed an effective technique based on the real-time TaqMan PCR system, which allows us to evaluate the copynumbers of the PARK2 gene exons by comparing the intensity of the amplification signals from some exon of this gene with that of the β-globin gene (the internal control).

Results

We analyzed rearrangements in exons 1–12 of the PARK2 gene in 64 patients from Russia with early-onset Parkinson's disease. The frequency of these mutations in our patients was 14%.

Conclusion

We have developed a simple, accurate, and reproducible method applicable to the rapid detection of exon rearrangements in the PARK2 gene. It is suitable for the analysis of large patient groups, and it may become the basis for a diagnostic test.

Detection of compound heterozygous deletions in the parkin gene of fibroblasts in patients with autosomal recessive hereditary parkinsonism (PARK2)

Mutations in the parkin gene are a common cause of autosomal recessive, juvenile or early onset parkinsonism (PARK2). In this report, we use RT-PCR to detect compound heterozygous deletions of the parkin gene in fibroblasts from two cases of middle age-onset familial parkinsonism with lower extremities-dominant resting tremor and mild cogwheel rigidity. Although exonic amplification of the parkin gene showed a deletional mutation of exon 3-4, their family histories suggested that the deletional mutations were a compound heterozygous abnormality of discrete origin. Immunoblotting demonstrated that abundant Parkin protein was expressed in fibroblasts, but little expression was detected in lymphocytes. RT-PCR using RNA isolated from the patients' fibroblasts indicated a parkin mutation in this family that consisted of compound heterozygous deletions (del exon3-4/del exon3-5). These results suggest that RT-PCR using the patients' fibroblasts may be helpful for the detection of compound heterozygous abnormalities in the parkin gene.

Parkin disease in a Brazilian kindred: Manifesting heterozygotes and clinical follow-up over 10 years

We report on a large Brazilian kindred with young-onset parkinsonism due to either a homozygous or heterozygous mutation in parkin. A total of 6 members were affected: 5 were homozygous and 1 heterozygous for a deletion in exon 4. Two other heterozygotes also had extrapyramidal signs. All affected subjects showed characteristic features of parkin disease with foot dystonia and an excellent response to levodopa complicated by motor fluctuations and dyskinesia within 3 years of therapy. Careful clinical follow-up over 10 years showed the phenotype was similar in all the homozygotes with asymmetrical limb bradykinesia and early walking difficulties. Some acceleration of disability was observed in some of the cases as they entered the third decade of illness, but dementia was absent.

Differential expression of splice variant and wild-type parkin in sporadic Parkinson's disease

BACKGROUND

Altered splicing of parkin under cellular stress could lead to changes in gene expression and altered protein activity. The causative role of parkin in sporadic Parkinson's disease (PD) is unknown.

OBJECTIVES

We described a parkin splice variant (SV) in the substantia nigra and leukocytes of sporadic PD patients. Using a case control methodology, we investigated the exon 4 SV (E4SV) and wild-type parkin expression in the leukocytes of sporadic PD patients and healthy individuals.

METHODS/RESULTS

We identified a parkin E4SV in the substantia nigra and leukocytes of sporadic PD patients and controls by reverse transcriptase-polymerase chain reaction (PCR). The exon 4 (122 bp) deletion resulted in a reading frame shift over the junction of exons 3-5 and a stop codon (tga) 17 bp downstream from exon 3. The translated truncated protein was associated with a total loss of the two-RING finger functional domain. Utilizing TaqMan real-time PCR with probes located across the junction of exons 3-4 or 3-5, we demonstrated an over-expression of E4SV/wild-type parkin ratio in the leukocytes of sporadic PD patients compared to age-, gender-, and race-matched controls (p<0.0005). A multivariate regression analysis demonstrated that the ratio of E4SV/wild-type parkin expression increased with age in PD patients, but this was not observed in the controls (p<0.0005).

CONCLUSION

The relative expression of E4SV/wild type parkin was increased in sporadic PD compared to healthy controls. Based on our observations, further functional studies to determine the pathophysiologic role of E4SV in sporadic PD patients will be of importance.

Familial-associated mutations differentially disrupt the solubility, localization, binding and ubiquitination properties of parkin

Mutations in parkin are largely associated with autosomal recessive juvenile parkinsonism. The underlying mechanism of pathogenesis in parkin-associated Parkinson's disease (PD) is thought to be due to the loss of parkin's E3 ubiquitin ligase activity. A subset of missense and nonsense point mutations in parkin that span the entire gene and represent the numerous inheritance patterns that are associated with parkin-linked PD were investigated for their E3 ligase activity, localization and their ability to bind, ubiquitinate and effect the degradation of two substrates, synphilin-1 and aminoacyl-tRNA synthetase complex cofactor, p38. Parkin mutants vary in their intracellular localization, binding to substrates and enzymatic activity, yet they are ultimately deficient in their ability to degrade substrate. These results suggest that not all parkin mutations result in loss of parkin's E3 ligase activity, but they all appear to manifest as loss-of-function mutants due to defects in solubility, aggregation, enzymatic activity or targeting proteins to the proteasome for degradation.

Ubiquitin, proteasome and parkin

The ubiquitin-proteasome system (UPS) is important for intracellular proteolysis, and is responsible for a diverse array of biologically important cellular processes, such as cell-cycle progression, signaling cascades and developmental programs. This system is also involved in the protein quality control, which maintains the health of the cell. Thus, the UPS provides a clue for understanding of the molecular mechanisms underlying various neurodegenerative diseases. In the last decade, we witnessed a tremendous progress in uncovering the mechanisms of Parkinson's disease (PD). Of the several genes that can cause familial PD, parkin, the causative gene of autosomal recessive juvenile parkinsonism (ARJP), is of a special interest because it encodes an ubiquitin-protein ligase, which covalently attaches ubiquitin to target proteins, designating them for destruction by the proteasome. This review summarizes recent studies on the UPS pathway with a special reference to parkin, focusing on how parkin is linked to the pathogenesis of ARJP.

Parkin mutation dosage and the phenomenon of anticipation: a molecular genetic study of familial parkinsonism

Background

parkin mutations are a common cause of parkinsonism. Possessing two parkin mutations leads to early-onset parkinsonism, while having one mutation may predispose to late-onset disease. This dosage pattern suggests that some parkin families should exhibit intergenerational variation in age at onset resembling anticipation. A subset of familial PD exhibits anticipation, the cause of which is unknown. The aim of this study was to determine if anticipation was due to parkin mutation dosage.

Methods

We studied 19 kindreds that had early-onset parkinsonism in the offspring generation, late-onset parkinsonism in the parent generation, and ≥ 20 years of anticipation. We also studied 28 early-onset parkinsonism cases without anticipation. Patients were diagnosed by neurologists at a movement disorder clinic. parkin analysis included sequencing and dosage analysis of all 12 exons.

Results

Only one of 19 cases had compound parkin mutations, but contrary to our postulate, the affected relative with late-onset parkinsonism did not have a parkin mutation. In effect, none of the anticipation cases could be attributed to parkin. In contrast, 21% of early-onset parkinsonism patients without anticipation had parkin mutations.

Conclusion

Anticipation is not linked to parkin, and may signify a distinct disease entity.

Distribution, type, and origin of Parkin mutations: review and case studies

Early-onset Parkinson's disease (PD) has been associated with different mutations in the Parkin gene (PARK2). To study distribution and type of Parkin mutations, we carried out a comprehensive literature review that demonstrated two prominent types of mutations among 379 unrelated mutation carriers: exon rearrangements involving exon 3, 4, or both, and alterations in exons 2 and 7, suggesting mutational hot spots or founders. To elucidate the origin of 14 recurrent Parkin mutations in our samples, we carried out a detailed haplotype analysis at the PARK2 locus. Thirty-eight mutation-positive individuals, available family members, and 62 mutation-negative individuals were genotyped. We determined allele frequencies and linkage disequilibrium (LD) to evaluate the significance of shared haplotypes. We observed no LD between markers at PARK2. Our data support a common founder for the most frequent Parkin point mutation (924C>T; exon 7) and indicate a mutational hot spot as cause of a common small deletion (255/256delA; exon 2). Furthermore, the most frequent Parkin exon deletion (Ex4del) arose independently in 2 of our subjects. However, it also occurred as the result of a founder mutation in 2 cases that shared identical deletion break points. This study provides evidence for both mutational hot spots and founder mutations as a source of recurrent mutations in Parkin, regardless of the mutation type.

parkin mutation analysis in clinic patients with early-onset Parkinson [corrected] disease

parkin Mutations are the most common identified cause of Parkinson's disease (PD). It has been suggested that patients with young-onset PD be screened for parkin mutations as a part of their clinical work-up. The aim of this study was to assess parkin mutation frequency in a clinical setting, correlate genotype with phenotype, and evaluate the current justification for clinical parkin testing. Patients were selected from a movement disorder clinic based on diagnosis of PD and onset age </=40 years. parkin was genotyped by sequence and dosage analysis for all 12 exons. Key relatives and controls were screened for identified mutations. Mutations were found in 7/39 patients. Two patients were compound heterozygous; five were heterozygous. Mutations included deletions in exons 2, 3, and 8, duplications in exons 2-4, and 9, and P437L substitution. Seventy-eight percent of mutations were deletions/multiplications. A novel substitution (R402W) was found in one patient and in one control. None of the point mutations found in patients were detected in 96 controls. parkin phenotypes were consistent with idiopathic PD. In conclusion, parkin mutations are common in the clinic setting: 10% of PD patients had early-onset and 18% of them had parkin mutations. However, if parkin is recessive, only 5% of early-onset cases who had compound mutations could be attributed to this locus. Mutation frequency was 0.12 (95% CI 0.04-0.19). parkin cases can present as typical idiopathic PD, distinguishable only by molecular testing. Seventy percent of parkin cases were heterozygous. It is unclear whether heterozygous mutations are pathogenic. parkin-based diagnosis and counseling require a better understanding of the mode of inheritance, penetrance, and carrier frequencies.

Novel parkin mutations detected in patients with early-onset Parkinson's disease

A multiethnic series of patients with early-onset Parkinson's disease (EOP) was studied to assess the frequency and nature of parkin/PARK2 gene mutations and to investigate phenotype-genotype relationships. Forty-six EOP probands with an onset age of < 45 years, and 14 affected relatives were ascertained from Italy, Brazil, Cuba, and Turkey. The genetic screening included direct sequencing and exon dosage using a new, cost-effective, real-time polymerase chain reaction method. Mutations were found in 33% of the indexes overall, and in 53% of those with family history compatible with autosomal recessive inheritance. Fifteen parkin alterations (10 exon deletions and five point mutations) were identified, including four novel mutations: Arg402Cys, Cys418Arg, IVS11-3C > G, and exon 8-9-10 deletion. Homozygous mutations, two heterozygous mutations, and a single heterozygous mutation were found in 8, 6, and 1 patient, respectively. Heterozygous exon deletions represented 28% of the mutant alleles. The patients with parkin mutations showed significantly earlier onset, longer disease duration, more frequently symmetric onset, and slower disease progression than the patients without mutations, in agreement with previous studies. This study confirms the frequent involvement of parkin and the importance of genetic testing in the diagnostic work-up of EOP.

A consanguineous Turkish family with early-onset Parkinson's disease and an exon 4 parkin deletion

The importance of parkin in early-onset Parkinson's disease in Japan, Europe, and the United States is well established. The contribution of this gene to the risk of Parkinson's disease in other populations is less well known. To explore the importance of parkin in those of Turkish ancestry, we studied familial cases from that country, and identified a consanguineous family with early-onset Parkinson's disease due to a homozygous mutation in parkin.

Diagnostic considerations in juvenile parkinsonism

Juvenile parkinsonism (JP) describes patients in whom the clinical features of parkinsonism manifest before 21 years of age. Many reported cases that had a good response to levodopa have proved to have autosomal recessive juvenile parkinsonism (AR-JP) due to mutations in the parkin gene. With the exception of parkin mutations and dopa-responsive dystonia, most causes are associated with the presence of additional neurological signs, resulting from additional lesions outside of the basal ganglia. Lewy body pathology has only been reported in one case, suggesting that a juvenile form of idiopathic Parkinson's disease may be extremely rare.

Parkin variants in North American Parkinson's disease: cases and controls

We report on an evaluation of coding variants within the parkin gene to assess their frequency in a North American clinical series of 313 Parkinson's disease (PD) cases and 192 unrelated controls. We hypothesized that the carrier frequency of parkin coding mutations, exon deletions, or duplications may be greater in PD cases. However, point mutations and exonic deletions/duplications, reported previously as pathogenic in homozygous or compound heterozygous individuals, occurred in both cases and controls with similar frequencies (3.8% in cases, 3.1% in controls). Furthermore, only stratified subanalyses detected any genetic association between the V380L common coding polymorphism and PD. We discuss the implication of parkin mutations for Parkinson's disease from this population perspective.

Mutation analysis of the parkin gene in Russian families with autosomal recessive juvenile parkinsonism

Autosomal recessive juvenile parkinsonism (AR-JP) is a form of hereditary parkinsonism characterized by variable clinical presentations and caused by mutations in a novel gene, parkin, on chromosome 6q25.2-27. Until now, no Russian cases of parkin-associated AR-JP have been reported on. We recruited 16 patients from 11 Russian families with dopa-responsive movement disorders according to the following criteria: 1) family history compatible with autosomal recessive inheritance; 2) onset of symptoms at </=30 years of age; and 3) the lack of mutations in the GTP cyclohydrolase I gene (in sporadic cases). Mutation screening of the parkin gene was carried out by a semiquantitative PCR assay and direct sequencing of the coding region. Six different parkin mutations (both deletions and point mutations) were identified in the index cases from four families, including a novel point mutation in the donor splice site (IVS1+1G-->A). The majority of our parkin-associated cases were characterized by early-onset dopa-responsive parkinsonism with benign course and slow progression (5 patients from two families have been followed for as long as 18-36 years), and 1 patient had a phenotype of dopa-responsive dystonia. This first description of Russian patients with AR-JP and molecularly proven parkin mutations confirms the widespread occurrence of this polymorphic hereditary extrapyramidal disorder.

How much phenotypic variation can be attributed to parkin genotype?

To establish phenotype-genotype correlations in early-onset parkinsonism, we have compared the phenotype of a large series of 146 patients with and 250 patients without parkin mutations. Although no single sign distinguished the groups, patients with mutations had significantly earlier and more symmetrical onset, dystonia more often at onset and hyperreflexia, slower progression of the disease, and a tendency toward a greater response to levodopa despite lower doses. After forward stepwise multiple logistic regression analysis, dystonia at onset and brisk reflexes were not longer significantly different but were correlated with age at onset rather than the presence of the parkin mutation. Age at onset in carriers of parkin mutations varied as did the rate of progression of the disease: the younger the age at onset the slower the evolution. The genotype influenced the phenotype: carriers of at least one missense mutation had a higher United Parkinson's Disease Rating Scale motor score than those carrying two truncating mutations. The localization of the mutations was also important because missense mutations in functional domains of parkin resulted in earlier onset. Patients with a single heterozygous mutation had significantly later and more asymmetrical onset and more frequent levodopa-induced fluctuations and dystonia than patients with two mutations.

Marked variation in clinical presentation and age of onset in a family with a heterozygous parkin mutation

Parkin gene mutations have been detected in families with early-onset autosomal recessive parkinsonism. We report a novel heterozygous 40 base pair deletion in exon 3 of the parkin gene that increases the susceptibility of carriers to develop parkinsonism/dystonia and manifests remarkable variability in regard to age of onset and phenotype in a single family. After identifying the new mutation in the proband of this kindred, family members were contacted and evaluated by a movement disorders specialist using standardized protocols and prospectively set diagnostic criteria. Importantly, examining physicians and family members were blinded to the genetic testing. Five affected members in two generations carried the parkin mutation. The proband and one of his brothers had disease onset at 24 years of age while another brother had disease at age 44. One exhibited multi-focal dystonia and parkinsonism of 17 years duration, another suffered a unilateral slowly progressive parkinsonism over 13 years while the third suffered dystonia-parkinsonism of recent onset. A sibling pair in the preceding generation had mild previously undiagnosed parkinsonism. Clinicians should be aware that patients carrying a parkin gene mutation may present with dystonia-parkinsonism or very subtle parkinsonism with a markedly varied age of onset.

Parkin mutations are frequent in patients with isolated early-onset parkinsonism

Parkin gene mutations are reported to be a major cause of early-onset parkinsonism (age at onset < or = 45 years) in families with autosomal recessive inheritance and in isolated juvenile-onset parkinsonism (age at onset <20 years). However, the precise frequency of parkin mutations in isolated cases is not known. In order to evaluate the frequency of parkin mutations in patients with isolated early-onset parkinsonism according to their age at onset, we studied 146 patients of various geographical origin with an age at onset < or = 45 years. All were screened for mutations in the parkin gene using semi-quantitative polymerase chain reaction combined with sequencing of the entire coding region. We identified parkin mutations in 20 patients including three new exon rearrangements and two new missense mutations. These results, taken in conjunction with those of our previous study (Lücking et al., 2000) show that parkin mutations account for at least 15% (38 out of 246) of our early-onset cases without family history, but that the proportion decreases significantly with increasing age at onset. There were no clinical group differences between parkin cases and other patients with early-onset parkinsonism. However, a single case presenting with cerebellar ataxia several years before typical parkinsonism extends the spectrum of parkin related-disease.

Parkin disease: a phenotypic study of a large case series

Mutations in the parkin gene, PARK2, are a common cause of parkinsonism in familial as well as isolated cases with an age of onset <40 years and should be considered in the diagnostic work up of young-onset parkinsonism. We report a detailed clinical evaluation of a personal series of 24 patients with mutations in the parkin gene. The clinical presentation of most cases was broadly comparable to that of previous descriptions of autosomal recessive early-onset or juvenile parkinsonism and young-onset Parkinson's disease and also had similarities with phenotypes of dopa-responsive dystonia. However, our only case with consanguineous parents had an age of onset of 54 years. We report three new phenotypes at presentation: cervical dystonia; autonomic dysfunction and peripheral neuropathy; and pure exercise-induced dystonia. We emphasize a number of clinical features that can be seen in parkin disease: focal dystonia; early instability; freezing; festination or retropulsion; concurrent autonomic failure; dramatic response to anticholinergics; early or atypical L-dopa-induced dyskinesias; exquisite sensitivity to small doses of L-dopa; and recurrent psychosis, even taking L-dopa alone. We also report behavioural disorder prior to the onset of parkinsonism. Some relatives carrying a single parkin mutation without extrapyramidal symptoms or signs also had psychiatric symptoms that might be related to their carrier status.

Mutation screening and association analysis of the parkin gene in Parkinson's disease patients from South-West China

Various deletions and point mutations in the Parkin gene have been strongly associated with Parkinson's disease (PD) and parkinsonism, especially when the onset occurs at a young age. In this study, we screened 25 "early-onset" (<49 years at onset) and 91 later-onset PD patients from a Han Chinese population from South-West China for deletions and mutations in the Parkin gene. We found no deletions or point mutations in exons 1-12 of the Parkin gene using direct sequence analysis and only detected the common Ser167Asn polymorphism. We analysed Ser167Asn in 116 patients with sporadic PD and 124 controls, matched for age and gender. There were significant differences in allele and genotype frequency between PD patients, with the 167Asn allele more common in cases than controls (46.6 vs. 35.1%; chi(2) = 6.54, p = 0.011, odds ratio = 1.61, 95% confidence interval, CI, 1.10-2.37), as was the 167Asn genotype (17.3 vs. 11.3%; p = 0.04). The frequency of the 167Ser genotype was significantly lower in PD patients than in controls when compared with that of the other two genotypes combined (chi(2) = 7.84, p = 0.005, odds ratio = 0.46, 95% CI 0.25 - 0.82). No significant differences in the frequencies of the allele and genotypes were found between patients classified into two groups according to symptoms at onset (chi(2) = 0.191, p = 0.66, odds ratio = 1.12, 95% CI 0.65-1.95; chi(2) = 0.24, p = 0.887) or age of onset (p = 0.787). In summary, homozygous deletion mutations and point mutations in exons 1-12 of the Parkin gene were not detected in this Han Chinese population, although we cannot exclude compound heterozygous deletions. In addition, our study suggests that the variant 167Asn increases the risk of developing PD.

Pseudo-autosomal dominant inheritance of PARK2: two families with parkin gene mutations

We report two families (Family S and Family N) with early-onset parkinsonism in two generations. The mode of inheritance appeared to be autosomal dominant, however, haplotye analysis suggested linkage to chromosome 6q25.2-27, the PARK2 locus, and all affected members were homozygotes in their haplotypes. In Family S, the affected father was married to unaffected mother, who carried one disease-linked haplotype at chromosome 6q25.2-27. In Family N, the unaffected mother carried one disease-linked haplotype. Quantitative PCR amplification analysis revealed exon 3 deletion in Family S and exon 5 deletion in Family N. The age of onset was from 18 to 22 years in Family S and 25 to 42 years in Family N. In both of their hometowns, most people lived in the same districts for many generations and consanguineous marriages had been common. Thus, the carrier state of the parkin gene might have been high in those communities, and marriage of a patient and a carrier is expected to result in autosomal dominant like inheritance. We conclude that PARK2 cannot be excluded even if the mode of inheritance appears as autosomal dominant, when the affected patients are young.

Point mutation in the parkin gene on patients with Parkinson's disease

To investigate the distribution of possible novel mutations from parkin gene in variant subset of patients with Parkinson's disease (PD) in China and explore whether parkin gene plays an important role in the pathogenesis of PD, 70 patients were divided into early-onset group and late-onset group; 70 healthy subjects were included as controls. Genomic DNA from 70 normal controls and from those of PD patients were extracted from peripheral blood leukocytes by using standard procedures. Mutations of parkin gene (exon 1-12) in all the subjects were screened by PCR-single strand conformation polymorphism (SSCP), and further sequencing was performed in the samples with abnormal SSCP results, in order to confirm the mutation and its location. A new missense mutation Gly284Arg in a patient and 3 abnormal bands in SSCP electrophoresis from samples of another 3 patients were found. All the DNA variants were sourced from the samples of the patients with early-onset PD. It was concluded that Parkin point mutation also partially contributes to the development of early-onset Parkinson's disease in Chinese.

Genetics of Parkinson's disease and biochemical studies of implicated gene products

Parkinson's disease was thought, until recently, to have little or no genetic component. This notion has changed with the identification of three genes, and the mapping of five others, that are linked to rare familial forms of the disease (FPD). The products of the identified genes, alpha-synuclein (PARK 1), parkin (PARK 2), and ubiquitin-C-hydrolase-L1 (PARK 5) are the subject of intense cell-biological and biochemical studies designed to elucidate the underlying mechanism of FPD pathogenesis. In addition, the complex genetics of idiopathic PD is beginning to be unraveled. Genetic information may prove to be useful in identifying new therapeutic targets and identifying the preclinical phase of PD, allowing treatment to begin sooner.

Complex relationship between Parkin mutations and Parkinson disease

Mutations in the Parkin gene cause juvenile and early onset Parkinsonism. While Parkin-related disease is presumed to be an autosomal-recessive disorder, cases have been reported where only a single Parkin allele is mutated and raise the possibility of a dominant effect. In this report, we re-evaluate twenty heterozygous cases and extend the mutation screening to include the promoter and intron/exon boundaries. Novel deletion, point and intronic splice site mutations are described, along with promoter variation. These data, coupled with a complete review of published Parkin mutations, confirms that not only is recessive loss of Parkin a risk factor for juvenile and early onset Parkinsonism but that Parkin haplo-insufficiency may be sufficient for disease in some cases.