G309D and W437OPA PINK1 mutations in Caucasian Parkinson's disease patients

PINK1 p.K520RfsX3 mutation identified in a Chinese family with early-onset Parkinson's disease

Parkinson's disease (PD) features selective loss of dopaminergic neurons of the substantia nigra pars compacta accompanied by the accumulation and aggregation of alpha-synuclein in Lewy bodies. PTEN induced putative kinase 1 gene (PINK1) mutations are the second most common genetic cause of autosomal recessive early-onset Parkinson's disease (EOPD). A single nucleotide deletion in PINK1 exon 8 (c.1557delG) was identified in a consanguineous Chinese family with EOPD. The homozygous deletion was co-segregated with disease in the family and resulted in a frameshift after codon 520 with a premature termination at codon 522 (p.K520RfsX3). These findings have significant implications on genetic counseling for the family and may be helpful in considering potential pathogenesis-targeted and disease-modifying strategies which should further improve patient quality of life.

Mutation screening of the HDC gene in Chinese Han patients with Tourette syndrome

Tourette Syndrome (TS) is a complex neuropsychiatric disorder characterized by vocal and motor tics. While environmental causes have been proposed to play a role, genetic factors are believed to be the main determinants of the disorder and its clinical manifestations. Recently, a heterozygous W317X mutation in the histidine decarboxylase gene (HDC) was reported to be responsible for TS in a two-generation pedigree. To investigate whether the HDC gene play a role in TS in Chinese Han population, we performed genetic analysis of the coding region of the HDC gene in 100 Chinese Han patients with TS. Three variants were found including a C > T transition (IVS1 + 52C > T), a novel C > A transition (c.426C > A) in exon 4, and a novel G > A transition (c.1743G > A) in exon 12, both predicted with no amino acid change. Extended analysis was conducted in a total of 120 TS patients and 240 sex, age, and ethnicity matched healthy controls. No significant differences in genotypic and allele distribution between patients and controls for these three variants (P = 0.274, P = 1.000 and P = 0.632 for genotypic distribution, respectively; P = 0.143, P = 1.000 and P = 0.582 for allele distribution, respectively) were observed, suggesting variants in the HDC gene may play little or no role in TS susceptibility in Chinese Han population.

Examination of the MSX1 gene in patients with Parkinson's disease

BACKGROUND

Several genetic variants in transcription factor genes have been reported to be associated with Parkinson's disease (PD). The muscle segment homeobox drosophila homolog of 1 gene (MSX1) is a major upstream regulator of the dopaminergic neuronal subtype specification.

AIMS OF THE STUDY

To determine whether genetic variation in the coding region of the MSX1 gene plays a role in the etiology of PD.

METHODS

We searched for genetic variations in the coding region of the MSX1 gene in 202 patients with PD and 200 normal controls by PCR-single-strand conformation polymorphism (PCR-SSCP) and sequencing.

RESULTS

No mutation in the MSX1 gene was identified in our cohort.

CONCLUSIONS

Mutations in the coding region of the MSX1 gene play little or no role in the development of PD.

Transcription factor PITX3 gene in Parkinson's disease

PITX3 is a transcription factor important for the differentiation and survival of midbrain dopaminergic neurons during the development. Recent reports suggest that single nucleotide polymorphisms (SNP) in the gene may be associated with Parkinson's disease (PD). To verify their findings and to determine the nature of the association in a subset of our PD patients we have analyzed two PITX3 SNPs (rs2281983 and rs4919621) in 265 PD patients and compared them with 210 age-matched healthy controls. Our data show that the substitutions of C/T in SNP1 and A/T in SNP2 are significantly higher in PD, and this finding is even more robust in young onset and familial PD as compared with age-matched healthy controls. Our findings indicate that PITX3 may play a role in the pathogenesis of PD.

Significance of the parkin and PINK1 gene in Jordanian families with incidences of young-onset and juvenile parkinsonism

BACKGROUND

Parkinson's disease is a progressive neurodegenerative disorder, where most cases are sporadic with a late onset. In rare incidences familial forms of early-onset parkinsonism occur, and when recessively inherited, cases are often explained by mutations in either the parkin (PARK2) or PINK1 (PARK6) gene or on exceptional occasions the DJ-1 (PARK7) or ATP13A2 (PARK9) gene. Recessively inherited deletions/duplications and point mutations in the parkin gene are the most common cause of early-onset parkinsonism known so far, but in an increasing number of studies, genetic variations in the serine/threonine kinase domain of the PINK1 gene are found to explain early-onset parkinsonism.

METHODS

In this study all families were from a population with a high incidence of consanguinity. We investigated 11 consanguineous families comprising 17 affected with recessively inherited young-onset parkinsonism for mutations both in the parkin and PINK1 gene. Exons and flanking regions were sequenced, and segregation patterns of genetic variation were assessed in members of the respective families. An exon dosage analysis was performed for all exons in both genes.

RESULTS

In the parkin gene, a three generation family was identified with an exon 4 deletion segregating with disease. Both affected were homozygous for the deletion that segregated on a haplotype that spanned the gene in a haplotype segregation analysis that was performed using additional markers. Exon dosage analysis confirmed the recessive pattern of inheritance with heterozygous deletions segregating in healthy family members. In the PINK1 gene we identified two novel putative pathogenic substitutions, P416R and S419P, located in a conserved motif of the serine/threonine kinase domain. Both substitutions segregated with disease in agreement with a recessive pattern of inheritance within respective families and both were present as homozygous in two affected each. We also discuss common polymorphisms in the two genes found to be co-segregating within families.

CONCLUSION

Our results further extend on the involvement of PINK1 mutations in recessive early-onset parkinsonism with clinical features similar to carriers of parkin mutations.

Genetic factors involved in the pathogenesis of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease characterized by a loss of nigrostriatal dopaminergic neurons. Recently, PD research has been stimulated by the identification of genes that are implicated in rare familial forms of PD. However, despite these discoveries, the primary cause of PD is still unclear. Various pathogenic mechanisms may be involved including mitochondrial dysfunction, proteasomal dysfunction/protein aggregation, oxidative damage, environmental factors and genetic disposition. Furthermore, dopamine has also been implicated in contributing to the pathogenesis of PD. This review will focus on the genes that have been identified to be associated with PD and how they may impair dopamine metabolism. Understanding the role of these PD-related genes in dopamine neurobiology may provide insight into the underpinning pathogenic mechanisms of PD.

PINK1 homozygous W437X mutation in a patient with apparent dominant transmission of parkinsonism

We analyzed the PINK1 gene in 58 patients with early-onset Parkinsonism and detected the homozygous mutation W437X in 1 patient. The clinical phenotype was characterized by early onset (22 years of age), good response to levodopa, early fluctuations and dyskinesias, and psychiatric symptoms. The mother, heterozygote for W437X mutation, was affected by Parkinson's disease and 3 further relatives were reported affected, according to an autosomal dominant transmission.

C-terminal truncation and Parkinson's disease-associated mutations down-regulate the protein serine/threonine kinase activity of PTEN-induced kinase-1

The Parkinson's disease (PD) causative PINK1 gene encodes a mitochondrial protein kinase called PTEN-induced kinase 1 (PINK1). The autosomal recessive pattern of inheritance of PINK1 mutations suggests that PINK1 is neuroprotective and therefore loss of PINK1 function causes PD. Indeed, overexpression of PINK1 protects neuroblastoma cells from undergoing neurotoxin-induced apoptosis. As a protein kinase, PINK1 presumably exerts its neuroprotective effect by phosphorylating specific mitochondrial proteins and in turn modulating their functions. Towards elucidation of the neuroprotective mechanism of PINK1, we employed the baculovirus-infected insect cell system to express the recombinant protein consisting of the PINK1 kinase domain either alone [PINK1(KD)] or with the PINK1 C-terminal tail [PINK1(KD+T)]. Both recombinant enzymes preferentially phosphorylate the artificial substrate histone H1 exclusively at serine and threonine residues, demonstrating that PINK1 is indeed a protein serine/threonine kinase. Introduction of the PD-associated mutations, G386A and G409V significantly reduces PINK1(KD) kinase activity. Since Gly-386 and Gly-409 reside in the conserved activation segment of the kinase domain, the results suggest that the activation segment is a regulatory switch governing PINK1 kinase activity. We also demonstrate that PINK1(KD+T) is approximately 6-fold more active than PINK1(KD). Thus, in addition to the activation segment, the C-terminal tail also contains regulatory motifs capable of governing PINK1 kinase activity. Finally, the availability of active recombinant PINK1 proteins permits future studies to search for mitochondrial proteins that are preferentially phosphorylated by PINK1. As these proteins are likely physiological substrates of PINK1, their identification will shed light on the mechanism of pathogenesis of PD.

Small interfering RNA targeting the PINK1 induces apoptosis in dopaminergic cells SH-SY5Y

PTEN-induced kinase 1 (PINK1) is a recently identified gene, mutations of which cause levodopa-responsive parkinsonism. An over-expression of wild-type PINK1 protects neurons from stress-induced mitochondrial dysfunction and apoptosis. We studied the effects of PINK1 suppression using small interfering RNA (siRNA), which can inhibit PINK1 mRNA expression up to 87%, and decrease PINK1 protein up to 80% in human dopaminergic cell line SH-SY5Y. Incubation with PINK1 siRNA decreased SH-SY5Y cell viability and significantly increased MPP(+) or rotenone-induced cytotoxicity. Our results indicate that reduction in PINK1 expression can trigger apoptotic process that can be exacerbated by the presence of MPP(+) or rotenone. These findings support the hypothesis that PINK1 participates in the protection of dopaminergic neurons.