Small-area distribution of multiple sclerosis incidence in western France: in search of environmental triggers.

BACKGROUND: Despite intensive research over several decades, the etiology of multiple sclerosis (MS) remains poorly understood, although environmental factors are supposedly implicated. Our goal was to identify spatial clusters of MS incident cases at the small-area level to provide clues to local environmental risk factors that might cause or trigger the disease. METHODS: A population-based and multi-stage study was performed in the French Brittany region to accurately ascertain the clinical onset of disease during the 2000-2004 period. The municipality of residence at the time of clinical onset was geocoded. To test for the presence of MS incidence clusters and to identify their approximate locations, we used a spatial scan statistic. We adjusted for socioeconomic deprivation, known to be strongly associated with increased MS incident rates, and scanned simultaneously for areas with either high or low rates. Sensitivity analyses (focusing on relapsing-remitting forms and/or places of residence available within the year following clinical onset) were performed. RESULTS: A total of 848 incident cases of MS were registered in Brittany, corresponding to a crude annual incidence rate of 5.8 per 100,000 inhabitants. The spatial scan statistic did not find a significant cluster of MS incidence in either the primary analysis (p value ≥ 0.56) or in the sensitivity analyses (p value ≥ 0.16). CONCLUSION: The findings of this study indicate that MS incidence is not markedly affected across space, suggesting that in the years preceding the first clinical expression of the disease, no environmental trigger is operative at the small-area population level in the French Brittany region.

REEP1 mutations in SPG31: frequency, mutational spectrum, and potential association with mitochondrial morpho-functional dysfunction.

Hereditary spastic paraplegias (HSP) constitute a heterogeneous group of neurodegenerative disorders characterized at least by slowly progressive spasticity of the lower limbs. Mutations in REEP1 were recently associated with a pure dominant HSP, SPG31. We sequenced all exons of REEP1 and searched for rearrangements by multiplex ligation-dependent probe amplification (MLPA) in a large panel of 175 unrelated HSP index patients from kindreds with dominant inheritance (AD-HSP), with either pure (n = 102) or complicated (n = 73) forms of the disease, after exclusion of other known HSP genes. We identified 12 different heterozygous mutations, including two exon deletions, associated with either a pure or a complex phenotype. The overall mutation rate in our clinically heterogeneous sample was 4.5% in French families with AD-HSP. The phenotype was restricted to pyramidal signs in the lower limbs in most patients but nine had a complex phenotype associating axonal peripheral neuropathy (= 5/11 patients) including a Silver-like syndrome in one patient, and less frequently cerebellar ataxia, tremor, dementia. Interestingly, we evidenced abnormal mitochondrial network organization in fibroblasts of one patient in addition to defective mitochondrial energy production in both fibroblasts and muscle, but whether these anomalies are directly or indirectly related to the mutations remains uncertain.

Evidence for a two-stage disability progression in multiple sclerosis.

It is well documented that disability accumulation in multiple sclerosis is correlated with axonal injury and that the extent of axonal injury is correlated with the degree of inflammation. However, the interdependence between focal inflammation, diffuse inflammation and neurodegeneration, and their relative contribution to clinical deficits, remains ambiguous. A hypothesis might be that early focal inflammation could be the pivotal event from which all else follows, suggesting the consideration of multiple sclerosis as a two-stage disease. This prompted us to define two phases in the disease course of multiple sclerosis by using two scores on the Kurtzke Disability Status Scale as benchmarks of disability accumulation: an early phase, 'Phase 1', from multiple sclerosis clinical onset to irreversible Disability Status Scale 3 and a late phase, 'Phase 2', from irreversible Disability Status Scale 3 to irreversible Disability Status Scale 6. Outcome was assessed through five parameters: Phase 1 duration, age at Disability Status Scale 3, time to Disability Status Scale 6 from multiple sclerosis onset, Phase 2 duration and age at Disability Status Scale 6. The first three were calculated among all patients, while the last two were computed only among patients who had reached Disability Status Scale 3. The possible influence of early clinical markers on these outcomes was studied using Kaplan-Meier estimates and Cox models. The analysis was performed in the Rennes multiple sclerosis database (2054 patients, accounting for 26,273 patient-years) as a whole, and according to phenotype at onset (1609 relapsing/445 progressive onset). Our results indicated that the disability progression during Phase 2 was independent of that during Phase 1. Indeed, the median Phase 2 duration was nearly identical (from 6 to 9 years) irrespective of Phase 1 duration (<3, 3 to <6, 6 to <10, 10 to <15, >or=15 years) in the whole population, and in both phenotypes. In relapsing onset multiple sclerosis, gender, age at onset, residual deficit after the first relapse and relapses during the first 2 years of multiple sclerosis were found to be independent predictive factors of disability progression, but only during Phase 1. Our findings demonstrate that multiple sclerosis disability progression follows a two-stage process, with a first stage probably dependent on focal inflammation and a second stage probably independent of current focal inflammation. This concept has obvious implications for the future therapeutic strategy in multiple sclerosis.

Genetic analysis of multiple sclerosis in Europeans: French data.

We report the results of a genome-wide screen for linkage disequilibrium (LD) in multiple sclerosis (MS) performed on 200 cases, 200 controls and 200 case-parent trios from France employing pooled DNA methodology. A total of 3510 microsatellite markers supplied through the GAMES collaborative were analysed and ranked according to their evidence for association. The most promising 117 markers were then followed up in a two-step validation process. In the first step, additional PCR of the DNA pools was performed in order to refine the ranking order. In the second step, markers were genotyped in individual cases and parents from the trio families. Seven markers showing nominally significant allele frequency differences between affected and unaffected emerged-D6S265, D12S1064, TNFa, D7S1824, D14S1426, D14S605 and D21S2051. These potential associations will require confirmation in further studies.

NOD2/CARD15 gene polymorphisms in Crohn's disease: a genotype- phenotype analysis.

OBJECTIVES: Three recently identified NOD2/CARD15 mutations have been described associated with an increased susceptibility Crohn's disease (CD). Our aim was to examine the potential association of these NOD2 mutations with CD and different subsets of CD phenotypes in our population. METHODS: Two hundred and five well-defined CD patients from north-western France and 95 ethnically matched healthy controls were genotyped for mutations R702W, G908R and Leu1007insC by DNA sequencing. Allele and genotype frequencies of NOD2 variants were examined in the whole series of CD and in different subgroups of CD phenotypes defined by the clinical characteristics of the Vienna classification (age at diagnosis, location and behaviour) or by histological features (granuloma). RESULTS: Carriers of at least one NOD2/CARD15 variant were significantly more frequent in CD than in controls (38.0% versus 20.0%, P < 0.002), and the R702W allele was the most significant contributor to this NOD2 association with CD. Homozygotes and compound heterozygotes combined had a higher risk of CD (odds ratio = 12.0, P < 0.0026) than simple heterozygotes for any variant (odds ratio = 2.2, P < 0.013) compared with subjects with no variant. Univariate analysis revealed that carriage of at least one NOD2 mutation was significantly associated with ileal involvement (P < 0.03), and stricturing evolution (P < 0.0015). Granuloma was associated with an excess of the R702W allele (16.1% versus 8.0%, Pc < 0.035), and was correlated with a young age at diagnosis, whatever the NOD2/CARD15 genotype. Multivariate analysis demonstrated that carriage of NOD2/CARD15 mutants, especially R702W, was primarily and independently associated both with stricturing evolution of CD and the presence of granuloma. CONCLUSIONS: In our population, all NOD2/CARD15 mutant genotypes, especially compound heterozygosity, were found to increase the risk of CD, but R702W was the sole allele showing a significant association with CD. In addition, we confirm the positive and independent association of the R702W mutation with stricturing behaviour and describe a second one with the presence of granuloma.

FOunder effect in patients with Unverricht-Lundborg disease on reunion island.

PURPOSE: Unverricht-Lundborg disease (ULD) is the most frequent form of progressive myoclonus epilepsy. ULD is caused mostly by a homozygous expansion of a dodecamer repeat in the cystatin B gene (CSTB) promoter. We present here a clinical and molecular study of 14 ULD patients originating from Reunion Island, a French island in the Indian Ocean. METHODS: These ULD patients were clinically evaluated, and the diagnosis of ULD was confirmed molecularly. We analyzed 12 microsatellites flanking CSTB and estimated the date of introduction of the ULD mutation on Reunion Island. RESULTS: These cases were clinically very similar, with the typical myoclonus syndrome associated with generalized tonic-clonic seizures, cerebellar involvement and, in some cases, mild mental deterioration. The mean age at onset was 9.6 years (range, 5-14 years), and the mean disease duration was 27 years (range, 5-47 years). The 14 patients harbored the typical ULD mutation, with variable degrees of expansion (mean of 56.3 repeats; range, 49-63). A founder effect was detected, with all but one of the Reunion ULD chromosomes displaying expansions belonging to the same haplotype, 1-1-1-2-6-4-3. We estimated the date of arrival of the most recent common ancestor (MRCA) of these patients on Reunion Island to the middle of the eighteenth century. CONCLUSIONS: These Reunion ULD patients displayed a homogeneous phenotype. Our molecular results are compatible with the instability of the repeat expansion and revealed a founder effect in Reunion ULD patients and the existence of a MRCA about 12 generations ago.

Genetic interaction of CTLA-4 with HLA-DR15 in multiple sclerosis patients.

Multiple sclerosis is a chronic inflammatory disease of the central nervous system with a genetic component. Until now, the more consistent association with the disease is found with the major histocompatibility complex, especially HLA-DRB1*1501-DQB1*0602 haplotype. In this report, we demonstrate the interaction of Cytotoxic T Lymphocyte-associated antigen 4 (CTLA-4 [CD152]) gene with DRB1*15 haplotype in multiple sclerosis genetic susceptibility. Our data were obtained from two European independent family-based studies including 610 multiple sclerosis family trios. Ann Neurol 2003;54:119-122

Investigation of seven proposed regions of linkage in multiple sclerosis: an American and French collaborative study.

Multiple sclerosis (MS) is a demyelinating autoimmune disease with a strong yet complex genetic component. To date only the HLA-DR locus, and specifically the HLA-DR15 allele, has been identified and confirmed as influencing the risk of developing MS. Genomic screens on several datasets have been performed and have identified several chromosomal regions with interesting results, but none have yet been confirmed. We tested seven of the most-promising regions (on chromosomes 1p, 2p, 3p, 3q, 5q, 19q, and Xp) identified from several genomic screens in a dataset of 98 multiplex MS families from the United States and 90 multiplex MS families from France. The results did not confirm linkage to 2p, 3q, 5q, or Xp in the overall dataset, or in subsets defined by geographic origin or HLA-DR15 status. Regions on 1p34, 3p14, and 19q13 produced lod scores >0.90 in at least one subset of the data, suggesting that these regions should be examined in more detail.