CYP2D6-debrisoquine hydroxylase gene polymorphism in multiple system atrophy

Multiple system atrophy: genetic or epigenetic?

Multiple system atrophy (MSA) is a rare, late-onset and fatal neurodegenerative disease including multisystem neurodegeneration and the formation of α-synuclein containing oligodendroglial cytoplasmic inclusions (GCIs), which present the hallmark of the disease. MSA is considered to be a sporadic disease; however certain genetic aspects have been studied during the last years in order to shed light on the largely unknown etiology and pathogenesis of the disease. Epidemiological studies focused on the possible impact of environmental factors on MSA disease development. This article gives an overview on the findings from genetic and epigenetic studies on MSA and discusses the role of genetic or epigenetic factors in disease pathogenesis.

Genetic players in multiple system atrophy: unfolding the nature of the beast

Multiple system atrophy (MSA) is a fatal oligodendrogliopathy characterized by prominent α-synuclein inclusions resulting in a neuronal multisystem degeneration. Until recently MSA was widely conceived as a nongenetic disorder. However, during the last years a few postmortem verified Mendelian pedigrees have been reported consistent with monogenic disease in rare cases of MSA. Further, within the last 2 decades several genes have been associated with an increased risk of MSA, first and foremost the SNCA gene coding for α-synuclein. Moreover, genes involved in oxidative stress, mitochondrial dysfunction, inflammatory processes, as well as parkinsonism- and ataxia-related genes have been implicated as susceptibility factors. In this review, we discuss the emerging evidence in favor of genetic players in MSA.

Genetic players in multiple system atrophy: unfolding the nature of the beast

Multiple system atrophy (MSA) is a fatal oligodendrogliopathy characterized by prominent α-synuclein inclusions resulting in a neuronal multisystem degeneration. Until recently MSA was widely conceived as a nongenetic disorder. However, during the last years a few postmortem verified Mendelian pedigrees have been reported consistent with monogenic disease in rare cases of MSA. Further, within the last 2 decades several genes have been associated with an increased risk of MSA, first and foremost the SNCA gene coding for α-synuclein. Moreover, genes involved in oxidative stress, mitochondrial dysfunction, inflammatory processes, as well as parkinsonism- and ataxia-related genes have been implicated as susceptibility factors. In this review, we discuss the emerging evidence in favor of genetic players in MSA.

Genetic variants of the alpha-synuclein gene SNCA are associated with multiple system atrophy

Background

Multiple system atrophy (MSA) is a progressive neurodegenerative disorder characterized by parkinsonism, cerebellar ataxia and autonomic dysfunction. Pathogenic mechanisms remain obscure but the neuropathological hallmark is the presence of α-synuclein-immunoreactive glial cytoplasmic inclusions. Genetic variants of the α-synuclein gene, SNCA, are thus strong candidates for genetic association with MSA. One follow-up to a genome-wide association of Parkinson's disease has identified association of a SNP in SNCA with MSA.

Methodology/Findings

We evaluated 32 SNPs in the SNCA gene in a European population of 239 cases and 617 controls recruited as part of the Neuroprotection and Natural History in Parkinson Plus Syndromes (NNIPPS) study. We used 161 independently collected samples for replication. Two SNCA SNPs showed association with MSA: rs3822086 (P = 0.0044), and rs3775444 (P = 0.012), although only the first survived correction for multiple testing. In the MSA-C subgroup the association strengthened despite more than halving the number of cases: rs3822086 P = 0.0024, OR 2.153, (95% CI 1.3–3.6); rs3775444 P = 0.0017, OR 4.386 (95% CI 1.6–11.7). A 7-SNP haplotype incorporating three SNPs either side of rs3822086 strengthened the association with MSA-C further (best haplotype, P = 8.7×10⁻⁴). The association with rs3822086 was replicated in the independent samples (P = 0.035).

Conclusions/Significance

We report a genetic association between MSA and α-synuclein which has replicated in independent samples. The strongest association is with the cerebellar subtype of MSA.

Trial Registration

ClinicalTrials.gov NCT00211224. [NCT00211224]

Epidemiological evidence on multiple system atrophy

Multiple system atrophy (MSA), is a sporadic neurodegenerative disorder characterized clinically by any combination of parkinsonian, autonomic, cerebellar or pyramidal symptoms and signs. The frequence of disease is estimated for the incidence rate to 0.6 cases per 100.000 person-years, while the prevalence rate is included between 1.86 and 4.9 cases per 100.000 pop. A risk factor seems to be the occupational history of farming also if the occupational exposure to pesticides is not associated with MSA. Smoking is probably a protective factor in MSA as Parkinson's disease. MSA seems a sporadic disease also if recently a German family with two MSA cases has been reported. The polymorphism association studies support a role for inflammation-related genes in risk for MSA. The current epidemiological and clinical evidence suggests that likely the etiopathogenesis of MSA is complex, and that many genetic as well as environmental factors are involved. Unfortunately, the most of studies in MSA are lacking in a sample size estimate to test the hypothesis, then the scientific evidence is poor. Then, much larger numbers of cases and controls are necessary for these studies to reach sufficient power, but collecting such large numbers is feasible only in the framework of multicentric consortia.

Frequencies of single nucleotide polymorphism in alcohol dehydrogenase7 gene in patients with multiple system atrophy and controls

A polymerase chain reaction and direct sequencing of the ADH7 gene were carried out in 50 controls and 50 patients with probable multiple system atrophy (MSA). Seven SNPs, one insertion, and one mismatch were found in patients with MSA and controls. There was no significant difference in the frequencies of each SNP between the patients and the controls (P > 0.05). Interpretation of this negative finding should be cautious in view of the relatively small number of cases.

Polymorphic cytochromes P450 and drugs used in psychiatry

1. The cytochrome P450 monooxygenases, CYP2D6, CYP2C19, and CYP2C9, display polymorphism. CYP2D6 and CYP2C19 have been studied extensively, and despite their low abundance in the liver, they catalyze the metabolism of many drugs. 2. CYP2D6 has numerous allelic variants, whereas CYP2C19 has only two. Most variants are translated into inactive, truncated protein or fail to express protein. 3. CYP2C9 is expressed as the wild-type enzyme and has two variants, in each of which one amino acid residue has been replaced. 4. The nucleotide base sequences of the cDNAs of the three polymorphic genes and their variants have been determined, and the proteins derived from these genes have been characterized. 5. An absence of CYP2D6 and/or CYP2C19 in an individual produces a poor metabolizer (PM) of drugs that are substrates of these enzymes. 6. When two drugs that are substrates for a polymorphic CYP enzyme are administered concomitantly, each will compete for that enzyme and competitively inhibit the metabolism of the other substrate. This can result in toxicity. 7. Patients can be readily phenotyped or genotyped to determine their CYP2D6 or CYP2C19 enzymatic status. Poor metabolizers (PMs), extensive metabolizers (EMs), and ultrarapid metabolizers (URMs) can be identified. 8. Numerous substrates and inhibitors of CYP2D6, CYP2C19, and CYP2C9 are identified. 9. An individual's diet and age can influence CYP enzyme activity. 10. CYP2D6 polymorphism has been associated with the risk of onset of various illnesses, including cancer, schizophrenia, Parkinson's disease, Alzheimer's disease, and epilepsy.

The CYP2D6B allele is not overrepresented in a population of German patients with idiopathic Parkinson's disease

The frequency of the CYP2D6B allele of the gene for debrisoquine 4-hydroxylase was studied in 115 patients with sporadic idiopathic Parkinson's disease, 55 of their healthy siblings, 63 patients with familial Parkinson's disease, 55 unaffected relatives, and 92 patients with Alzheimer's disease and 73 age matched healthy controls. By contrast with several previous studies, no significant variation of allele frequencies could be found between any of the groups studied. The results argue against a significant role of the CYP2D6 gene in the aetiology of sporadic and familial idiopathic parkinsonism in this patient population.

The GTP-cyclohydrolase I gene in atypical parkinsonian patients: a clinico-genetic study

GTP cyclohydrolase I (GTPCH) has recently been identified as the first causative gene for Dopa-responsive dystonia (DRD). DRD typically presents with dystonia in the lower limbs in childhood, but may produce an akinetic-rigid syndrome in middle and old age. We have sequenced the GTPCH gene in 29 Parkinsonian patients without a positive family history for DRD, but who shared at least one feature of the akinetic-rigid presentation of DRD: 23 patients had at least one living relative who also suffered from an akinetic-rigid syndrome; 2 patients had an abnormally mild course of their parkinsonism which was extremely dopa-responsive. DNA was also analysed from 4 brain samples of patients who were clinically diagnosed as suffering from Parkinson's disease, but then did not show any pathological findings at post mortem. No changes in the sequence of the GTPCH gene were detected. We conclude that so far there is no evidence that mutations of the GTPCH gene are responsible for the development of parkinsonism in patients without a positive family history of DRD.

Neuromyotonia in association with malignant hyperpyrexia

Images