Larissa Arning

Ataxia with oculomotor apraxia type 2: clinical, biological and genotype/phenotype correlation study of a cohort of 90 patients

Ataxia with oculomotor apraxia type 2 (AOA2) is an autosomal recessive disease due to mutations in the senataxin gene, causing progressive cerebellar ataxia with peripheral neuropathy, cerebellar atrophy, occasional oculomotor apraxia and elevated alpha-feto-protein (AFP) serum level. We compiled a series of 67 previously reported and 58 novel ataxic patients who underwent senataxin gene sequencing because of suspected AOA2. An AOA2 diagnosis was established for 90 patients, originating from 15 countries worldwide, and 25 new senataxin gene mutations were found. In patients with AOA2, median AFP serum level was 31.0 microg/l at diagnosis, which was higher than the median AFP level of AOA2 negative patients: 13.8 microg/l, P = 0.0004; itself higher than the normal level (3.4 microg/l, range from 0.5 to 17.2 microg/l) because elevated AFP was one of the possible selection criteria. Polyneuropathy was found in 97.5% of AOA2 patients, cerebellar atrophy in 96%, occasional oculomotor apraxia in 51%, pyramidal signs in 20.5%, head tremor in 14%, dystonia in 13.5%, strabismus in 12.3% and chorea in 9.5%. No patient was lacking both peripheral neuropathy and cerebellar atrophy. The age at onset and presence of occasional oculomotor apraxia were negatively correlated to the progression rate of the disease (P = 0.03 and P = 0.009, respectively), whereas strabismus was positively correlated to the progression rate (P = 0.03). An increased AFP level as well as cerebellar atrophy seem to be stable in the course of the disease and to occur mostly at or before the onset of the disease. One of the two patients with a normal AFP level at diagnosis had high AFP levels 4 years later, while the other had borderline levels. The probability of missing AOA2 diagnosis, in case of sequencing senataxin gene only in non-Friedreich ataxia non-ataxia-telangiectasia ataxic patients with AFP level > or =7 microg/l, is 0.23% and the probability for a non-Friedreich ataxia non-ataxia-telangiectasia ataxic patient to be affected with AOA2 with AFP levels > or =7 microg/l is 46%. Therefore, selection of patients with an AFP level above 7 microg/l for senataxin gene sequencing is a good strategy for AOA2 diagnosis. Pyramidal signs and dystonia were more frequent and disease was less severe with missense mutations in the helicase domain of senataxin gene than with missense mutations out of helicase domain and deletion and nonsense mutations (P = 0.001, P = 0.008 and P = 0.01, respectively). The lack of pyramidal signs in most patients may be explained by masking due to severe motor neuropathy.

New genomic region for Wegener's granulomatosis as revealed by an extended association screen with 202 apoptosis-related genes.

Wegener’s granulomatosis (WG) is a systemic disease with complex genetic background. It is characterized by necrotizing granulomatous inflammation of the upper and lower respiratory tract, glomerulonephritis, vasculitis and the presence of antineutrophil cytoplasmatic autoantibodies (C-ANCAs) in sera of patients. Here, we report on an extended association screen (EAS) with 202 microsatellite markers, representing apoptosis-related genes and further genes down-regulated in apoptotic neutrophils, using pooled DNA of 150 Northern German patients suffering from WG and 100 healthy Northern German controls. Six microsatellite allele patterns were found significantly associated with WG, three of which could be confirmed by individual genotyping. One marker remained significantly associated after multiple corrections. This marker representing the retinoid X receptor ß gene (RXRB, P=7.60×10−6, distance to gene: ~5.3xa0kb) is localised in the major histocompatibility complex (MHC) region between the HLA-DPB1 and DAXX genes. HLA-DPB1 typing and fine mapping of the region with additional microsatellites and single-nucleotide polymorphisms (SNPs) revealed a strong association of WG with the significantly over-represented DPB1*0401 (P=1.51×10−10, OR=3.91) allele compared with the control cohort. In addition, an extended haplotype DPB1*0401/RXRB03 was identified showing an even stronger association with WG (P=7.13×10−17, OR=6.41). These results represent the strongest association of a genomic region with WG, suggesting a major genetic contribution in the aetiology of the disease. Thus, our data demonstrate that EAS may be a valuable alternative approach for determining genetic predisposition factors in multifactorial diseases.

NR2A and NR2B receptor gene variations modify age at onset in Huntington disease

Abstract. N -Methyl- d -aspartate (NMDA) receptor-mediated excitotoxicity has been proposed to play a role in the pathogenesis of Huntington disease (HD), an autosomal dominantly inherited disorder associated with defined expansions in a stretch of perfect CAG repeats in the 5′ part of the IT15 gene. The number of CAG repeat units is highly predictive for the age at onset (AO) in HD. However, AO is only modestly correlated with repeat length when the HD expansion range is in the high 30s or low 40s. Therefore, we investigated whether the genes for the different subunits composing the multimeric complexes of NMDA receptors (GRIN glutamate receptor, ionotropic, Nn-methyl- d -aspartate) represent candidates for modulating the AO of HD. In the studied cohort of 167 HD patients, the repeat range from 41 to 45 CAG units accounted for 30.8% of the variance in AO; 12.3% additional variance could be attributed tonGRIN2B genotype variation and 4.5% to GRIN2A genotype variation. We conclude that these two genes, coding for NR2B and NR2A subtypes mainly expressed in the striatum, may influence the variability in AO of HD. Neuroprotective strategies for HD patients and persons at risk should be reconsidered in the light of these findings.

Efficacy of Fumaric Acid Esters in the R6/2 and YAC128 Models of Huntington's Disease

Huntingtons disease (HD) is an autosomal dominantly inherited progressive neurodegenerative disease. The exact sequel of events finally resulting in neurodegeneration is only partially understood and there is no established protective treatment so far. Some lines of evidence speak for the contribution of oxidative stress to neuronal tissue damage. The fumaric acid ester dimethylfumarate (DMF) is a new disease modifying therapy currently in phase III studies for relapsing-remitting multiple sclerosis. DMF potentially exerts neuroprotective effects via induction of the transcription factor “nuclear factor E2-related factor 2” (Nrf2) and detoxification pathways. Thus, we investigated here the therapeutic efficacy of DMF in R6/2 and YAC128 HD transgenic mice which mimic many aspects of HD and are characterized by an enhanced generation of free radicals in neurons. Treatment with DMF significantly prevented weight loss in R6/2 mice between postnatal days 80–90. At the same time, DMF treatment led to an attenuated motor impairment as measured by the clasping score. Average survival in the DMF group was 100.5 days vs. 94.0 days in the placebo group. In the histological analysis on day 80, DMF treatment resulted in a significant preservation of morphologically intact neurons in the striatum as well as in the motor cortex. DMF treatment resulted in an increased Nrf2 immunoreactivity in neuronal subpopulations, but not in astrocytes. These beneficial effects were corroborated in YAC128 mice which, after one year of DMF treatment, also displayed reduced dyskinesia as well as a preservation of neurons. In conclusion, DMF may exert beneficial effects in mouse models of HD. Given its excellent side effect profile, further studies with DMF as new therapeutic approach in HD and other neurodegenerative diseases are warranted.

PGC-1alpha as modifier of onset age in Huntington disease

Although there is a strong correlation between CAG repeat length and age at onset (AO) of motor symptoms, individual Huntington disease (HD) patients may differ dramatically in onset age and disease manifestations despite similar CAG repeat lengths. This has led to a search for genetic factors that influence AO. In order to identify such a genetic modifier, we analysed polymorphisms in the PGC-1alpha gene. Recent data indicate inhibition of PGC-1alpha function by mutant Htt supporting a link between transcriptional deregulation and mitochondrial dysfunction in HD. In > 400 HD patients, a polymorphism located within intron 2, a potential recombination hot spot, explains a small, but statistically significant, amount of the variability in AO. Our data suggest that PGC-1alpha has modifying effects on the pathogenic process in HD.

The Wegener's granulomatosis quantitative trait locus on chromosome 6p21.3 as characterised by tagSNP genotyping.

Background: A genomic region on chromosome 6p21.3, including HLA-DPB1, has been linked to Wegener’s granulomatosis (WG). The basis of this association is difficult to evaluate because of the complex haplotype block architecture of this region. Objective: To identify the causative molecular genetic variation(s) using a detailed HapMap based fine-mapping approach. Methods: 282 patients with WG and 380 healthy controls were genotyped for HLA-DPB1 as well as for 35 informative single nucleotide polymorphisms (SNPs) within the respective region. 25 of these SNPs have been selected as tagging SNPs for another 219 associated SNPs. Allele and genotype frequencies were analysed separately by contingency tables and logistic regression. Finally, the coding region of RING1 was directly sequenced in subjects who carried haplotypes that were correlated with contrasting WG risks. Results: The previously reported strong association of WG with the HLA-DPB1*0401 allele was confirmed in an independent WG sample (nu200a=u200a108, pcu200a=u200a6.4×10−8). When the complete cohort (nu200a=u200a282) was considered, the association remained highly significant in ANCA-positive (pcu200a=u200a1.26×10−22), but not in ANCA-negative patients. An SNP 3′ of HLA-DPB1 yielded the smallest p value and was associated with WG partly independently from the HLA-DPB1 alleles. Another informative SNP in the vicinity of RING1 showed significant WG association that was also partly independent of HLA-DPB1. RING1 sequencing, however, did not show any variation potentially predisposing to WG. Conclusions: The HLA-DPB1/RING1 region is strongly associated with WG in ANCA-positive subjects. Further analyses of potential cis regulatory sequences of candidate genes HLA-DPB1, RING1 and RXRB appear warranted.

Functionally relevant variations of the interleukin‐10 gene associated with antineutrophil cytoplasmic antibody–negative Churg‐Strauss syndrome, but not with Wegener's granulomatosis

OBJECTIVEnWegeners granulomatosis (WG) and Churg-Strauss syndrome (CSS) belong to the heterogeneous group of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides. Current understanding of their pathogenesis and genetic background is limited. Expression levels of interleukin-10 (IL-10), a potent and pleiotropic cytokine, are largely determined by variations in the gene encoding the IL-10 precursor. This study was undertaken to determine the impact of IL10 polymorphisms on the pathogenesis of both WG and CSS in large cohorts.nnnMETHODSnThree single-nucleotide polymorphisms (SNPs) tagging the promoter haplotypes of the IL10 gene (IL10 -3575, IL10 -1082, and IL10 -592) were analyzed in 403 patients with WG and 103 patients with CSS as well as 507 matched control subjects from Germany. In addition, 3 informative SNPs in other parts of IL10 were genotyped.nnnRESULTSnNone of the markers or their haplotypes was associated with WG or any of its subgroups classified according to ANCA status, sex, or presence of further WG genetic risk factors. In contrast, the IL10 -3575/-1082/-592 TAC haplotype, part of the extended ancient haplotype IL10.2, was highly significantly associated with ANCA-negative CSS (chi2 = 19.14, P = 0.000012, corrected P = 0.0003, odds ratio 2.16, 95% confidence interval 1.52-3.06).nnnCONCLUSIONnThese findings challenge those from previous studies of IL10 in WG and provide further evidence that CSS and WG have distinct genetic backgrounds. Because the IL10.2 haplotype has been correlated reproducibly with increased IL10 expression, the possible role of IL-10 in the pathogenesis of ANCA-negative CSS needs to be further elucidated.

The ontogenesis of language lateralization and its relation to handedness.

Dominance of the left hemisphere for many aspects of speech production and perception is one of the best known examples of functional hemispheric asymmetries in the human brain. Classic theories about its ontogenesis assume that it is determined by the same ontogenetic factors as handedness because the two traits are correlated to some extent. However, the strength of this correlation depends on the measures used to assess the two traits, and the neurophysiological basis of language lateralization is different from that of handedness. Therefore, we argue that although the two traits show partial pleiotropy, there is also a substantial amount of independent ontogenetic influences for each of them. This view is supported by several recent genetic and neuroscientific studies that are reviewed in the present article.

NR2A and NR2B receptor gene variations modify age at onset in Huntington disease in a sex-specific manner

In addition to the pathogenetic CAG repeat expansion other genetic factors play a significant role in determining age at onset (AO) in Huntington disease (HD), e.g. variations in the NR2A and NR2B glutamate receptor subunit genes (GRIN2A, GRIN2B). In order to expand these findings we fine-mapped a larger HD patient panel (nxa0=xa0250) using densely spaced markers flanking the originally associated SNPs in GRIN2A and GRIN2B. In GRIN2A association fine-mapping based on eight additional SNPs confirmed intron 2 as the region of strongest association. In GRIN2B fine-mapping with seven additional SNPs consolidated C2664T as causal genetic variation. Gender stratification of patients revealed differences in the variability in AO attributable to the CAG repeat number and highly significant differences in the AO association with the C2664T and rs8057394/ rs2650427 variations. Addition of the corresponding genotype variations to the effect of CAG repeat lengths resulted in a significant increase of the R2 values only in females. The sex-specific effect for C2664T is underscored by differences in the genotype and allele frequencies observed for female versus male HD patients (Pxa0=xa00.01) caused by decreased CC frequency in females. Overall, female HD patients homozygous for the CC genotype tended to have later AO compared to the other two genotypes. Stratification of the results by presumed menopausal status demonstrated that the significant findings were predominantly observed in pre-menopausal patients. We speculate that altered hormone levels herald protective effects of this genotype. Together, GRIN2A and GRIN2B genotype variations explain 7.2% additional variance in AO for HD.

PCSK6 VNTR Polymorphism Is Associated with Degree of Handedness but Not Direction of Handedness.

Although the left and right human cerebral hemispheres differ both functionally and anatomically, the mechanisms that underlie the establishment of these hemispheric specializations, as well as their physiological and behavioral implications, remain largely unknown. Since cerebral asymmetry is strongly correlated with handedness, and handedness is assumed to be influenced by a number of genetic and environmental factors, we performed an association study of LRRTM1 rs6733871 and a number of polymorphisms in PCSK6 and different aspects of handedness assessed with the Edinburgh handedness inventory in a sample of unrelated healthy adults (nu200a=u200a1113). An intronic 33bp variable-number tandem repeat (VNTR) polymorphism in PCSK6 (rs10523972) shows a significant association (significance threshold: p<0.0025, adjusted for multiple comparisons) with a handedness category comparison (Pu200a=u200a0.0005) and degree of handedness (Pu200a=u200a0.001). These results provide further evidence for the role of PCSK6 as candidate for involvement in the biological mechanisms that underlie the establishment of normal brain lateralization and thus handedness and support the assumption that the degree of handedness, instead the direction, may be the more appropriate indicator of cerebral organization.