The increasing incidence and prevalence of MS in a Sardinian province

High prevalence and fast rising incidence of multiple sclerosis in Caltanissetta, Sicily, southern Italy

BACKGROUND

Epidemiological studies conducted in Sicily and Sardinia, the two major Mediterranean islands, showed elevated incidence and prevalence of multiple sclerosis (MS)and a recent increase in disease frequency.

OBJECTIVE

To confirm the central highlands of Sicily as areas of increasing MS prevalence and elevated incidence, we performed a follow-up study based on the town of Caltanissetta (Sicily), southern Italy.

METHODS

We made a formal diagnostic reappraisal of all living patients found in the previous study performed in 1981. All possible information sources were used to search for patients affected by MS diagnosed according to the Poser criteria. We calculated prevalence ratios, for patients affected by MS who were living and resident in the study area on December 31, 2002. Crude and age- and sex-specific incidence ratios were computed for the period from January 1, 1993, to December 31, 2002.

RESULTS

The prevalence of definite MS rose in 20 years from 69.2 (retrospective prevalence rate) to 165.8/100,000 population. We calculated the incidence of definite MS for the period 1970-2000. These rates calculated for 5-year periods increased from 2.3 to 9.2/100,000/year.

CONCLUSION

This survey shows the highest prevalence and incidence figures of MS in the Mediterranean area and confirms central Sicily as a very-high-risk area for MS.

Sex ratio of multiple sclerosis in Canada: a longitudinal study

BACKGROUND

Incidence of multiple sclerosis is thought to be increasing, but this notion has been difficult to substantiate. In a longitudinal population-based dataset of patients with multiple sclerosis obtained over more than three decades, we did not show a difference in time to diagnosis by sex. We reasoned that if a sex-specific change in incidence was occurring, the female to male sex ratio would serve as a surrogate of incidence change.

METHODS

Since environmental risk factors seem to act early in life, we calculated sex ratios by birth year in 27 074 Canadian patients with multiple sclerosis identified as part of a longitudinal population-based dataset.

FINDINGS

The female to male sex ratio by year of birth has been increasing for at least 50 years and now exceeds 3.2:1 in Canada. Year of birth was a significant predictor for sex ratio (p<0.0001, chi(2)=124.4; rank correlation r=0.84).

INTERPRETATION

The substantial increase in the female to male sex ratio in Canada seems to result from a disproportional increase in incidence of multiple sclerosis in women. This rapid change must have environmental origins even if it is associated with a gene-environment interaction, and implies that a large proportion of multiple sclerosis cases may be preventable in situ. Although the reasons why incidence of the disease is increasing are unknown, there are major implications for health-care provision because lifetime costs of multiple sclerosis exceed pound1 million per case in the UK.

The epidemiology of multiple sclerosis in Europe

Multiple sclerosis (MS) is a chronic and potentially highly disabling disorder with considerable social impact and economic consequences. It is the major cause of non-traumatic disability in young adults. The social costs associated with MS are high because of its long duration, the early loss of productivity, the need for assistance in activities of daily living and the use of immunomodulatory treatments and multidisciplinary health care. Available MS epidemiological estimates are aimed at providing a measure of the disease burden in Europe. The total estimated prevalence rate of MS for the past three decades is 83 per 100,000 with higher rates in northern countries and a female:male ratio around 2.0. Prevalence rates are higher for women for all countries considered. The highest prevalence rates have been estimated for the age group 35-64 years for both sexes and for all countries. The estimated European mean annual MS incidence rate is 4.3 cases per 100,000. The mean distribution by disease course and by disability is also reported. Despite the wealth of epidemiological data on MS, comparing epidemiological indices among European countries is a hard task and often leads only to approximate estimates. This represents a major methodological concern when evaluating the MS burden in Europe and when implementing specific cost-of-illness studies.

Imaging brain damage in first-degree relatives of sporadic and familial multiple sclerosis

OBJECTIVE

Our objective was to assess brain damage in first-degree relatives of patients with sporadic and familial multiple sclerosis (MS).

METHODS

Asymptomatic first-degree relatives of sporadic (sMS, n = 152) and familial MS (fMS, n = 88) and healthy volunteers (NC, n = 56) underwent brain MRI and magnetization transfer (MT) imaging on a mobile MR scan. On MR examinations, we visually assessed white matter (WM) lesions and quantified WM lesion volumes, brain volumes, and MT ratio (MTr) in lesions and normal-appearing WM (NAWM).

RESULTS

A lesional MR pattern similar to that of MS patients was found in 4% sMS and 10% fMS. In these WM lesions, MTr was lower (p < 0.0001) than in the WM of NC. In contrast, there was no difference in NAWM-MTr and brain volume values between the three groups.

INTERPRETATION

Focal brain abnormalities indistinguishable from those of MS occur in asymptomatic first-degree relatives of MS patients. These are twice more frequent in fMS than in sMS but do not lead to the widespread tissue damage commonly found in MS patients. Although there is a genetic susceptibility to develop brain abnormalities suggestive of focal demyelination in first-degree relatives of MS patients, other factors are probably critical for the development of a diffuse, clinically relevant, pathology.

Bayesian mapping of multiple sclerosis prevalence in the province of Pavia, northern Italy

The geographical analysis of a disease risk is particularly difficult when the disease is non-frequent and the area units are small. The practical use of the Bayesian modelling, instead of the classical frequentist one, is applied to study the geographical variation of multiple sclerosis (MS) across the province of Pavia, Northern Italy. 464 MS-affected individuals resident in the province of Pavia were identified on December 31st 2000. The overall prevalence was 94 per 100,000 inhabitants. This estimate indicates an increasing MS prevalence in the province, in accordance with the vast majority of the Italian areas where prevalence studies have been repeated. We mapped the geographical variation of MS prevalence across the 190 communes of the province both with a classical approach and a Bayesian approach. The frequentist approach produced an extremely dishomogeneous map, while the Bayesian map was much smoother and more interpretable. Our study underlines the usefulness of Bayesian methods to obtain reliable maps of disease prevalence and to identify possible clusters of disease where to carry out further epidemiological investigations.

The prevalence of multiple sclerosis in the District of Santarém, Portugal

The prevalence of multiple sclerosis (MS) in Portugal is still unknown. Recent studies conducted in southern European countries showed higher than expected rates of MS prevalence. In an attempt to evaluate the MS prevalence in Santarém--a district with 62621 inhabitants (1991 census) located in the centre of Portugal--we have conducted a population survey in this district for five years. The crude prevalence rate found was 46.3/100,000. This figure is not different from findings recently reported in studies conducted at similar latitudes in neighbour southern European countries. This was the first population survey conducted in Portugal, and it is the first accurate contribution to the knowledge of the MS prevalence in this country.

Role of return migration in the emergence of multiple sclerosis in the French West Indies

The emergence of multiple sclerosis in island societies has been investigated only in a few Caucasian populations living in temperate regions. The effect of human migration on the risk of developing this disease is still an open question because of possible genetic selection. We conducted an epidemiological study of the multiple sclerosis population in the French West Indies (Martinique and Guadeloupe), a population which includes large numbers of West Indians who have returned after emigrating to metropolitan France. Standardized incidence ratios (SIRs) for multiple sclerosis among migrants were calculated and their genetic characteristics were compared to those of non-migrants. The crude prevalence of multiple sclerosis was 14.8/10(5) on December 31, 1999 (95% CI: 11.9-17.7); and its crude mean annual incidence for the period July 1, 1999 to June 30, 2002 was 1.4/10(5) (95% CI: 1.0-1.8), confirming its emergence in the French West Indies. Recurrent neuromyelitis optica, which is virtually the only form of multiple sclerosis in black African populations in tropical regions, represented not >17.8% of these cases. During the 1,440,000 person-years of follow-up, 33 incidence cases were identified in migrants. Since the number of expected cases was 19.3, the overall SIR was 1.71 (95% CI: 1.19-2.38; P < 0.01) among migrants. The increase in the SIR was more marked if the stay was made before the age of 15 years (4.05, 95% CI: 2.17-6.83; P < 0.0001). European ancestry in the two migrating and non-migrating populations was similar. Martinique, which has a higher rate of return migration, has a higher prevalence of multiple sclerosis (21.0/10(5) versus 8.5/10(5)) and a higher incidence (2.0/10(5) versus 0.7/10(5)) than Guadeloupe. The emergence of the disease in the French West Indies is of environmental rather than genetic origin. It may be explained either through the introduction by migrants of precipitating environmental factors that operate in a critical way before the age of 15 years, and/or by the recent disappearance from the French West Indies of protective environmental factors acting before this age.

Interaction of loci within the HLA region influences multiple sclerosis course in the Sardinian population

We examined the influence of alleles at the HLA loci, previously found to be associated with multiple sclerosis (MS) in Sardinia, on the clinical course of the disease in 835 relapsing (R) and 100 primary progressive (PP) patients. Multivariate analysis was carried out on predisposing 0301 or non-associated DPB1 alleles, susceptible or non-associated DRB1-DQB1 haplotypes, both predisposing and non-predisposing, and negatively and non-negatively associated D6S1683 alleles, taking interaction between them into account. Intra-patient analysis showed that the presence of the susceptible or protective D6S1683 allele interacting with predisposing DP 0301 modulated risk of PP disease. These findings suggest that a locus telomeric to HLA class I exerts an effect on alleles at the DPB1 locus in modulating disease course.

The prevalence of multiple sclerosis in the north?west Italian province of Genoa

The objective of this study was to assess the prevalence of multiple sclerosis (MS), calculated as point prevalence on 31 December 1997, in the province of Genoa, North-western Italy.

METHODS

The province of Genoa is located in North-western Italy, an area of 1,835 km(2). On the point prevalence day the population consisted of 913,218 inhabitants. MS cases were identified by analysing archives of the hospitals with neurological or rehabilitation wards, neurologists serving the community, files of local chapters of the Italian MS society, all requests for oligoclonal bands analysis on CSF in the studied area. Patients included in the study were MS cases diagnosed before 31 December 1997 according to the Poser criteria resident in the province under study.

RESULTS

A total of 857 subjects were alive and residing in the province of Genoa on the prevalence day. The overall crude prevalence rate was 94 per 100,000 (95% CI 88-100); 291 were males (34%) with a crude prevalence of 67 per 100,000 (95 % CI 60-76) and 566 were females (66%) with a prevalence of 118 per 100,000 (95% CI 108-128). The female/male ratio was 1.9. When age and sex were adjusted to the Italian standard population of 1991 prevalence was 85 per 100,000. Five hundred and thirty two out of the 857 patients agreed to be interviewed. The interviewed sample was representative of the prevalence sample: sex and gender distributions were identical in the two samples. The overall mean age was 48 (+/-13) years (48 +/-12 years in males; 48+/-14 years in females). Mean disease duration was 15 (+/-10) years for males and 16 (+/-11) years for females. Two hundred and ninety one (55 %) subjects had a relapsing remitting (RR) clinical course, 150 (28%) were secondary progressive (SP) and 91 (17%) were primary progressive (PP). Mean EDSS score was 5 (+/- 2; median 5). The mean age at time of onset was 33 (+/-10) years for males and 32 (+/- 11) years for females. The disease onset was monosymptomatic in 76% (n=407) patients and polysymptomatic in 24% (n=125). The mean length of time between clinical onset and diagnosis was 5 (+/- 6) years.

CONCLUSION

We confirmed that the province of Genoa is a very high risk area for MS. We found a high rate of patients with a PP course; also the proportion of patients with high disability scores is greater compared to previous studies.

Multiple sclerosis in twins from continental Italy and Sardinia: A nationwide study

Knowledge about the balance between heritable and nonheritable risk in multiple sclerosis (MS) is based on twin studies in high-prevalence areas. In a study that avoided ascertainment limitations and directly compared continental Italy (medium-prevalence) and Sardinia (high-prevalence), we ascertained 216 pairs from 34,549 patients. This gives a twinning rate of 0.62% among MS patients, significantly less than that of the general population. In continental Italy, probandwise concordance was 14.5% (95% confidence interval, 5.1-23.8) for monozygotic and 4.0% (95% confidence interval, 0.8-7.1) for dizygotic twins. Results in Sardinia resemble those in northern populations but in limited numbers. Monozygotic concordance was 22.2% (95% confidence interval, 0-49.3) probandwise, but no concordant dizygotic pairs were identified. A questionnaire on 80 items possibly related to disease cause was administered to 70 twin pairs, 135 sporadic patients, and 135 healthy volunteers. Variables positively (7) or negatively (2) associated with predisposition and concordance in twins largely overlapped and were mainly linked to infection. If compared with previous studies, our data demonstrate that penetrance in twins appears to correlate with MS prevalence. They highlight the relevance of nonheritable variables in Mediterranean areas. The apparent underrepresentation of MS among Italian twins draws attention to protective factors, shared by twins, that may influence susceptibility.

PTPRC (CD45) C77G mutation does not contribute to multiple sclerosis susceptibility in Sardinian patients

A linkage and association of the CD45 (protein-tyrosine phosphatase, receptor-type C) C77G polymorphism and multiple sclerosis (MS) has been found in some studies but not in others. We analysed the C77G polymorphism in MS patients from the genetically homogeneous population of Sardinia. Using the transmission disequilibrium test, the mutation has been sought in 241 patients and 217 healthy sibs (HS) from singleton MS families and it was found in 5 (2.07 %) affected and 3 (1.38%) HS from 7 heterozygous parents (1.45 %). Transmission of the G77 allele was 71.4 % (TDT = 1.3, P = 0.26) in patients and 50% (TDT = 0, P = 1) in HS. Stratifying families according to carriage of MS-predisposing (DR+) or not-predisposing (DR-) HLA-DR-DQ genotype in patients, percentage of G77 transmission to DR+ patients was 33 (TDT = 0.33, P = 0.56, Pc = 1.12), while it was 100 (TDT = 4, P = 0.045, Pc = 0.09) in the DR-patients. We concluded that, despite the presence of CD45 G77 polymorphism in a few patients who did not carry the HLADR- DQ MS-predisposing molecules, CD45 did not contribute to development of the disease in Sardinian MS.

Genes, environment, and susceptibility to multiple sclerosis

Multiple sclerosis (MS) is a chronic disease of the central nervous system affecting young adults and thus representing a major burden also for their families and communities. The etiology of MS is obscure and its pathogenesis is yet incompletely depicted. Increased evidences indicate a strong genetic contribution to MS susceptibility, although others support the view that it is also influenced by environmental factors, possibly related to still unidentified pathogens. MS appears to be more heterogeneous than previously believed at the immunological level, and new pathological studies indicate a series of subset of conditions under the common denominator MS. The use of genetically homogeneous and geographically isolated populations at high MS risk, such as that of Sardinia, insular Italy, becomes in principle a vital requirement to reduce biological variables and the intrinsic complexity of the disease. This review will focus on recent findings on the peculiarity of Sardinian MS concerning epidemiological, genetic, and environmental aspects. Epidemiological studies reveal a clear heterogeneous distribution of MS cases in the Northern province of Sassari which may not be uniquely assigned to genetic variations. Furthermore, a different immunogenetic profile, including the association with other immunomediated diseases, and a progressive change in clinical phenotype, including age at onset, are present in this island which gives us unexpected variations at the level of patients' cohort and territorial distribution, especially when the northern province is compared to the southern one. This renders MS etiopathogenesis more complex than formerly thought even in this selected and genetically stable population.

Multiple Sclerosis in Southern Europe: Monreale City, Italy

BACKGROUND

Several follow-up studies showed increasing prevalence and incidence rates for multiple sclerosis (MS).

OBJECTIVE

To ascertain, throughout a follow-up study, the incidence and prevalence of MS in the city of Monreale, Sicily, southern Italy.

METHODS

We calculated crude and age- and sex-specific prevalence rates on December 31, 2000, and determined incidence rates for the period January 1, 1992 to December 31, 2000.

RESULTS

The prevalence of MS was 71.2 per 100,000 population (48,5/100,000 in men; 93,0/100,000 in women). The incidence rate of MS for the period 1992-2000 was 4.0/100,000 per year.

CONCLUSION

This study showed a nonsignificant increase in MS incidence rates in Monreale city for 1992-2000 compared to 1981-1991. Prevalence rates were similar to those of the previous follow-up study. Intervals between onset of symptoms and diagnosis seemed shorter than in prior studies. There is no evidence that the high prevalence and incidence rates have changed in this interval but numbers are too small for firm statements. These findings indicate that in Monreale city MS prevalence is stable and confirm Sicily as a high-risk area for MS.

Multiple Sclerosis in its European Matrix: Some Aspects of History, Mechanisms and Treatment

Susceptibility to multiple sclerosis is influenced by several genes which are relatively common in populations of European origin. Their precise identification is currently being intensively investigated. The pathophysiology of the main clinical features is better understood.Relapseresults from abnormalities of conduction to which both demyelination and inflammation contribute. At the membrane level,remissiondepends on the formation of new sodium channels which restore conduction even in persistently demyelinated axons. Remyelination presumably contributes and synaptic reorganisation may also do so. Axonal degeneration contributes to irrecoverable deficit andprogressionof disability. These observations suggest new therapeutic strategies. The management of multiple sclerosis needs to be improved. Progress requires an ethically based partnership between patients, whose needs are paramount, the research and caring communities and the pharmaceutical industry.

A genome-wide screen for linkage disequilibrium in Sardinian multiple sclerosis

Using indirect whole genome association screening, we have searched for multiple sclerosis susceptibility genes in the genetically isolated high risk Sardinian population. Two screens were performed; the first was based on 229 cases and 264 unrelated controls, and the second on 235 trio families. Each screen employed a dense set of microsatellite markers and DNA pooling. Data from both screens were available from 2764 markers. Nine markers showed nominally significant results in both screens independently. Five of these markers-D2S408 (2q36), D6S271 (6p21), D6S344 (6p25), D7S1818 (7p12) and D16S420 (16p12)-remained nominally significant in both studies after conservative refining analysis.

Progressive increase in incidence and prevalence of multiple sclerosis in Newcastle, Australia: a 35-year study

The prevalence of multiple sclerosis (MS) in Newcastle, Australia increased significantly between 1961 and 1981 and the incidence of the disease also increased between the decades 1950-1959 and 1971-1981. The present study sought to determine whether there has been a further increase in the frequency of MS in the subsequent 15 years, and to examine the potential factors underlying this change. The incidence, prevalence and clinical profile of multiple sclerosis were therefore re-examined in Newcastle, Australia in 1996 using comparable diagnostic criteria and methods to those employed in studies in the same region in 1961 and 1981. There has been a significant progressive increase in prevalence from 19.6 to 59.1 per 100,000 population and a significant increase in incidence from 1.2 to 2.4 per 100,000 population from 1961 to 1996. The most pronounced increase in prevalence was in females and in the age-group over 60 years, and there was also an increased incidence in females aged 20-29 years. There was little change in the age of disease onset, but duration of disease in females had increased substantially. The significant increase in prevalence is attributed to increased incidence, particularly in females; and to increased survival. Although such trends in prevalence have been observed in the Northern Hemisphere, this is the first such study in the Southern Hemisphere to show a longitudinal increase in prevalence and incidence over a period of this duration.

Increasing frequency of multiple sclerosis in Padova, Italy: a 30 year epidemiological survey

OBJECTIVE

To determine the incidence and prevalence rates of multiple sclerosis (MS) and their temporal profiles over the last 30 years in the province of Padova (northeast Italy).

BACKGROUND

In the early 1970s an epidemiological survey in the province of Padova showed a MS prevalence and incidence of 16/100 000 and 0.9/100 000 population, respectively; these figures are much lower than current estimates in other regions of Italy and Central Europe.

METHODS

The population of the study area was approximately 820 000 (422 028 women, 398 290 men) in the 1991 census. All possible sources of case collection were used, but only clinically definite/probable and laboratory-supported definite/probable MS were considered in the analysis of incidence and prevalence trends from 1971 to 1999.

RESULTS

On 31 December 1999, the crude prevalence rate was 80.5/100 000 (95% CI 70.3-90.7); prevalence was higher in women (111.1/100 000; 95% CI 99.0-123.1) than in men (49.7/100 000; 95% CI 41.3-58.1). This difference was significant (F/M = 2.43; z = 10.1, P < 0,00001); a rate adjusted for the European population was 81.4/100 000. On 31 December 1980 and on 31 December 1990 the estimated prevalence rates were 18/100 000 and 45.7/100 000, respectively. Thus, a fivefold increase in prevalence was observed from the 1970s. The mean annual incidence was 2.2/100 000 in the period 1980-89, 3.9 in the period 1990-94 and 4.2 in the period 1995 99. Thus, incidence increased more than fourfold from the 1970s through 1994 and remained quite stable in the last several years. Mean age at onset was 31.3 +/- 9.88 years. Mean diagnostic latency decreased significantly from 49.2 +/- 44.5 months in 1985 to 23.0 +/- 30.3 months in 1990, 12.9 +/- 15.61 in 1995 and 5.3 +/- 4.7 in 1999.

CONCLUSIONS

The actual prevalence (80.5/100 000) and incidence (4.2/100 000) of MS in the province of Padova agree with the most recent epidemiological estimates/trends observed in other Italian and European areas, except for Sardinia and Scotland. The increase in both incidence and prevalence rates observed in much of this region over the last 30 years parallels the introduction of more sensitive diagnostic techniques and a highly significant decrease in diagnostic latency. These findings probably do not support a real increase in the frequency of MS in northeast Italy because recent estimates of incidence have increased only slightly (3.9 to 4.2, which is < 10% in five years) and increase in the prevalence rate was almost completely due to the accumulation of new incidence cases.

Multiple sclerosis in Malta in 1999: an update

OBJECTIVES

To ascertain the prevalence of multiple sclerosis (MS) in the islands of Malta and compare it with a previous study undertaken 21 years earlier, when a remarkably low prevalence was found.

METHOD

Deaths with MS on the death certificate since the last study were reviewed. Sources of information about new patients were the Hospital Activity Analysis scheme, the MS Society of Malta, the records of the state hospitals, long stay private hospitals and nursing homes, lists provided by the state pharmacies, and magnetic resonance imaging, cerebrospinal fluid, and evoked response studies. Prevalence day was 1 January 1999. The Poser classification was used.

RESULTS

Since 1978, 17 patients had died with a verified diagnosis of MS on the death certificate. They included all 10 deaths with MS from the original study and two immigrants. Fifty patients had clinically definite MS (CDMS) and 13 clinically probable MS (CPMS). The prevalence of CDMS was 13.2/100 000 (male 11.2, female 15.2). The prevalence of CDMS and CPMS combined was 16.7/100,000 (male 13.3, female 19.9). The annual incidence was 0.7/100,000. Twelve patients were found with CDMS among the 7213 immigrants resident in Malta (166/100,000). The expected rate was 1/100,000, determined at Maltese born rates. There were major changes in the population distribution during the 21 years between the two studies, with a big increase in the age groups with a high risk of MS. There is a longer expectation of life and the diagnosis in now made earlier.

CONCLUSION

Malta still has a low MS prevalence. In comparison with Sicily and other Mediterranean countries of Europe it offers an opportunity to ascertain the genetic and environmental factors responsible for the disease.

Multiple sclerosis complexity in selected populations: the challenge of Sardinia, insular Italy

Several lines of evidence indicate a genetic contribution to multiple sclerosis (MS) both in terms of predisposition to the disease and of immunological mechanisms which are known to play crucial roles in MS pathogenesis. The presence of high- and low-risk areas for MS in neighbouring regions supports the theory that MS predisposition is influenced by a complex interaction of genetic and environmental factors. Therefore, the use of genetically homogeneous and geographically isolated populations becomes an increasing requirement to reduce biasing biological variables. Sardinians fulfil these conditions well because of their different phylogeny from Europeans and the unique selective pressures which shaped their genome. Sardinians display amongst the highest MS prevalence rates world-wide and increasing MS incidence rates over time. Also, MS in Sardinia is linked to distinct human leucocyte antigen (HLA) alleles and associated to different patterns of cytokine production from lymphoid cells of different HLA subtypes. In this context, recent findings and future perspectives on the peculiarities of Sardinian MS concerning genetic, immunological and epidemiological aspects are presented. So far, our results indicate that variations at the level of territorial distribution and HLA-association are present which render MS heterogeneous even in this ethnically homogeneous population.

Patients with multiple sclerosis and risk of type 1 diabetes mellitus in Sardinia, Italy: a cohort study

BACKGROUND

Individuals from Sardinia, Italy, are at high risk of developing multiple sclerosis and type 1 diabetes mellitus. We attempted to assess the prevalence in this region of type 1 diabetes mellitus in individuals with multiple sclerosis, and to ascertain disease risk factors.

METHODS

We did a cohort study to assess prevalence of type 1 diabetes in 1090 people with multiple sclerosis, and in their parents (n=2180) and siblings (n=3300), all born and living in Sardinia. All participants were patients at the multiple sclerosis clinic in Cagliari, and were judged representative of the total Sardinian outpatients and inpatients. We asked patients whether their parents or siblings had multiple sclerosis or diabetes, confirming replies by examining clinical records. We identified risk factors for diabetes with univariate and multivariate logistic regression analyses.

FINDINGS

Diabetes prevalence in people with multiple sclerosis was, respectively, about three-fold and five-fold that in their healthy siblings (p=0.001) and in the general population (p<0.0001). Presence of other relatives with multiple sclerosis conferred increased risk of type 1 diabetes to healthy siblings of individuals with multiple sclerosis (odds ratio=3.41, p=0.0019). Diabetes risk was six-fold higher in patients with relatives having multiple sclerosis than in healthy siblings of multiple sclerosis patients without other relatives with the disease (p=0.0001).

INTERPRETATION

In Sardinian families with genetic inheritance of multiple sclerosis type 1 diabetes is prevalent, both in multiple sclerosis patients and in healthy siblings. This finding indicates that common genes contribute to susceptibility to both diseases in this population.

Genetic factors and the founder effect explain familial MS in Sardinia

OBJECTIVE

To estimate the presence of familial aggregation and determine the contribution of genetic factors to familial clustering of MS in patients coming from Sardinia, a Mediterranean island considered a genetically homogeneous, isolated area having high disease incidence and prevalence.

METHODS

Recurrence risk in siblings of 901 Sardinian patients and factors influencing risk (patient and sibling sex, patient age at onset, sibling birth cohort, and presence of affected relatives other than siblings) were examined. The presence of distant familial relationships among patients was evaluated by tracing the extended pedigrees of all patients with MS born in one Sardinian village.

RESULTS

Twenty-three brothers and 36 sisters of the 2,971 siblings were affected with MS. Recurrence risk was greater in siblings of index patients with onset age less than 30 years (p < 0.01, increased risk 2.33 times) and having a relative with MS other than a sibling or parent (p < 0.01, increased risk 2.90 times). Pedigree analysis of patients from the village of L. showed that all 11 patients descended from 3 pairs of ancestors, whereas no cases occurred in the remaining 2,346 inhabitants. In descendants from the 3 couples, MS prevalence was dramatically greater than the regional average and 1.5 times greater than that observed in siblings of affected cases.

CONCLUSIONS

Data from this study indicate that MS familial aggregation in Sardinians is influenced by genetic factors and that founder effect and the isolation of Sardinia can be considered causes of the enrichment of "etiologic" MS genes.

Multiple sclerosis distribution in northern Sardinia: spatial cluster analysis of prevalence

BACKGROUND

A heterogeneous geographic distribution of MS has been reported among different ethnic groups, and also within small communities. Epidemiologic studies conducted over the past two decades using repeated assessments clearly show that Sardinia is at high risk for MS, with a prevalence of 150 per 100,000 in 1997.

OBJECTIVE

To present spatial analysis of the disease prevalence to disclose possible "hot" or "cold" spots of disease, further allowing correlations with risk factors.

METHODS

A spatial analysis of the whole province of Sassari, in northern Sardinia, at a microgeographic level (i.e., in the 89 administrative communes and 6 linguistic areas) was conducted. Because of the small number of cases per commune and to overcome random variability, a hierarchical Bayesian approach was adopted. The distribution of prevalent cases by commune of residence on December 31, 1997 and from age 5 to 15 years was analyzed.

RESULTS

A clustering pattern was found in the southwestern communes of the province based on geographic distribution by both prevalence and residence at age 5 to 15 years. A west-to-east gradient also was observed.

CONCLUSIONS

This study highlights a hot spot of MS in the southwestern part of Sassari province, bordering with the commune of Macomer, where MS was once hypothesized as having occurred as an epidemic. Interestingly, these areas of MS clustering comprise the Common Logudorese linguistic domain. The Catalan area, linguistically and genetically distant from the remaining Sardinian domains, does not show such high estimates. Because MS is not a single-source infectious disease, this study may help test the hypothesis that a widely and evenly spread environmental (infectious?) agent may produce disease in subgroups of genetically more susceptible individuals in areas at higher inbreeding rates, wherein a disease mode of inheritance could be better investigated.

NKT cells and type-1 diabetes and the "hygiene hypothesis" to explain the rising incidence rates

Immune-mediated (type-1) diabetes (IMD) is a multigenetic disease that is strongly influenced by the environment. Whereas the incidence rates are steadily rising worldwide, less than half of affected identical twins ever become concordant for IMD or even beta-cell autoimmunity. Worldwide, it is the tropical regions of the world that are replete in infectious and parasitic diseases that are the least affected. Repeated efforts to identify the putative inductive agents for beta-cell autoimmunity have proved unrewarding. Rather, we suggest that some environments are less protective than others and argue that it is the fall in incidences of infectious diseases and intestinal parasites that are likely responsible for the rise in autoimmune diseases like IMD in the West. Nonobese diabetic (NOD) mice reared in gnotobiotic environments have only worsened diabetes, while recent studies suggest that multiple defects in immune tolerance to self must be present before IMD can develop in the human or mouse. We speculate herein that the deficiency in natural killer T (NKT) cells in IMD in both species may be both genetic and environmentally influenced, predisposing to pancreatic beta-cell autoimmunity through a dysfunction of immunoregulatory T cells, with defective peripheral control of islet cell protein autoreactive cytotoxic CD8+ T cells. The encouraging results in NOD mice using alpha-galactosylceramide to stimulate NKT cells now warrant trials with this and other glycolipid NKT cell-stimulating agents in humans. Since it has become apparent that autoimmune diseases such as IMD are the result of an underlying immunodeficiency state, we strongly argue that its effective prevention will likely come through the use of immunostimulation and not through side effect-prone immunosuppression.

Protective role of infections and vaccinations on autoimmune diseases

Infectious agents may induce autoimmune disease through several mechanisms, notably antigen mimicry and inflammation of the target organ; conversely, infections may protect from autoimmune diseases. This paradoxical effect has been demonstrated for a number of bacteria, viruses and parasites on a variety of spontaneous or experimentally induced animal models of autoimmune diseases (e.g. experimental allergic encephalomyelitis, lupus mice, non-obese diabetic mice). The mechanisms of the protection are still ill-defined, and probably vary according to models. Stimulation of immunoregulatory CD4 T cells has been shown to play a central role in several major models. The role of superantigens is also important, like that of Toll-like receptors. Antigen competition is another major mechanism, itself open to several interpretations. Epidemiological data support a protective role of infections on human allergic and autoimmune diseases. These diseases are much more common in countries with high socio-economic development (typically Northern countries in Europe). The reason for this cannot be fully explained by genetic differences because migrating populations develop these diseases with the same incidence of the adoptive country rather than that of the country of origin. It is interesting that the frequency of these diseases has been increasing in developed countries over the last 20 years but not in undeveloped ones.