The risk of multiple sclerosis on the Orkney islands. A review of the search for distinctively Orcadian risks, with a hypothesis for further investigations

The most extensive and meticulous epidemiological study yet to be published on the frequency of multiple sclerosis (MS) across the regions of Scotland has confirmed that the high incidence of MS on the Orcadian islands is unique and is most probably the highest in the world. Environmental and genetic studies of Orcadian MS have been carried out over many years but the results have been discouragingly inconclusive; no convincing explanation of the distinctively high Orcadian MS risks has come to light. However, studies of both prevalence and incidence of MS over a time line of approximately five decades, show that Orcadian MS has steadily increased to significantly exceed the neighbouring genetically related populations including North Eastern Scotland and the Shetland islands. Over this period the islands have progressively expanded occupations related to agriculture and have simultaneously acquired the highest concentration of cattle in Europe. Coinciding high and increasing Orcadian MS risk with increasing agricultural activities including bovine density and dairying, points towards a potential but unexpected causal risk. Raised incidence of MS with farming and in particular with dairy farming have been documented in Australia, Denmark, and more recently in Norway, further pointing to a possible MS risk associated with agricultural activities. A clue to the cause of this curious association has unexpectedly emerged from laboratory studies. Using very rarely available tissues from patients coming to autopsy during an MS attack, a toxin known as beta-haemolysin (sphingomyelinase), which is produced by the bacterium Staphylococcus aureus, has been identified in the affected tissues. Staph aureus is a common inhabitant of the mucosal linings of the human nasal sinuses and sinus mucosal inflammations have been shown to be closely associated with attacks of MS and optic neuritis. Irrespective of origin, human or animal, all strains of Staph aureus carry the beta haemolysin gene. However, the toxin is only sporadically expressed by the strains most commonly isolated from human carriers. Strains carried by bovines nearly always express toxin. Has the increasing high risk of MS in Orcadians been promoted by the nasal transmission and subsequent establishment of the high secreting bovine genotypes of Staph aureus in the Orcadian population? To demonstrate that bovine associated strains of Staph aureus are carried more frequently in the Orcadian population (or even specifically in Orcadian MS cases), would not of itself necessarily explain the high prevalence of Orcadian MS. It would however clearly justify an in-depth exploration of the nasal bacterial microbiome of MS cases. This should include the incidence of beta-toxin secreting Staph aureus genotypes. If MS cases are shown to have a distinctive nasal bacterial microbiome, including beta-toxin secretors, this finding would open up an almost entirely new range of investigations and approaches to the understanding of the pathogenesis of MS.

SNP heterozygosity, relatedness and inbreeding of whole genomes from the isolated population of the Faroe Islands

BACKGROUND

The population of the Faroe Islands is an isolated population but very little is known about it from whole genome sequencing. The population of about 50000 people has a high incidence of rare diseases e.g., 1:300 for Primary Carnitine Deficiency. A screening programme was implemented, and eleven persons were also whole genome sequenced at x37 coverage for diagnostic purposes of those cases that were not affected by the known mutations. The purpose of our study is to utilize the high coverage data to explore the genomic variation and the ancestral history of the population. We study the SNP heterozygosity, the pairwise relatedness from kinship, the inbreeding from runs of homozygosity ROH, and we find the minor allele frequency distribution. We estimate the population ancestry and the timing of the founding event by using the whole genomes from eight consenting individuals.

RESULTS

We find the number of SNPs and the heterozygosity for the eight individual samples, and for merged samples, for which we also study the relatedness. We find close relatedness between the supposedly unrelated individuals. From ROH, we interpret the high relatedness as an ancient property of the isolated population. A bottleneck event is estimated starting between years [Formula: see text] with a maximum consanguineous population in year [Formula: see text] and similarly consanguineous between years [Formula: see text]. The ancestry analysis shows the population descends from founders of [Formula: see text] European and [Formula: see text] Admixed American ancestry. A distinct clustering near the central European and British populations of the 1000 Genome Project is likely the result of the population isolation and genetic drift. The minor allele frequency distribution suggests many rare variants.

CONCLUSIONS

The ancestry is mainly European while the inbreeding is higher compared to European populations and population isolates. The Faroese population has inbreeding more like ancient Europeans. We discovered a bottlenecked and consanguineous population event and estimated it starting in the 1st-4th century as compared to the oldest archaeological findings from the 4th-6th century.

Triggering multiple sclerosis at conception and early gestation: The variation in ultraviolet radiation is as important as its intensity

Background and objectives

Medical science needs to further elucidate the role of ultraviolet radiation (UVR), geographic latitude, and the role of vitamin D in the autoimmune disease multiple sclerosis (MS). We separated several papers into categories out of the thousands published and used their conclusions to explore the relationship between UVR and MS.

Relevance

MS is increasing in incidence, particularly in women where MS is two to three times that in men and particularly severe in African Americans.

Methods

We collected UVR data at our observatory in Central Maine and calculated the average coefficient of variation (CVUVR) for each month for 15 years (2007-2021, inclusive).

Results

The month of conception (MOC) is more important than the month of birth (MOB) in explaining how UVR triggers the variable genetic predisposition to MS. We hypothesize that the rapidly increasing CVUVR is important in preventing an increase in the activity of the vitamin D receptor (VDR) from August to December, which then requires a higher intensity of UVR later in life to suppress the immune system, therefore predisposing to more MS.

Limitations

One observatory at about 44° latitude.

Conclusions

While variation in UVR is important at the MOC if UVR exceeds a threshold (e.g., if the sunspot number equals or is greater than 90, usually at a solar cycle MAX, or at elevations above approximately 3,000 feet above sea level), the MS mitigating vitamin D-VDR mechanism is overwhelmed and the genotoxic effects of higher-intensity UVR promote MS in those with a genetic predisposition.

What is new in this research

This paper offers a new concept in MS research.

Consanguineous marriage and its relevance to divorce, polygyny and survival of marriage: evidence from a population-based analysis in Jordan

BACKGROUND

Consanguinity has been extensively studied in the context of its negative health outcomes for offspring and socio-demographic factors, but little evidence-based research has been done on its potential social benefits.

AIM

To examine the association between consanguineous marriage and the risk of divorce or separation, polygyny, and survival of marriage in Jordan.

SUBJECTS AND METHODS

Data were obtained from the 2018 Jordan Population and Family Health Survey, covering a nationally representative sample of ever-married women of reproductive age. Descriptive statistics, multiple logistic regression, and survival analysis techniques were used for data analysis.

RESULTS

The prevalence of consanguineous marriage was found to be 27.5% in Jordan in 2018, while the prevalences of polygyny and divorced/separated rates were 4.4% and 4.7%, respectively. Both consanguineous and polygyny rates showed declining trends, but divorce/separation rate showed an increasing trend. Compared to non-consanguineous marriages, the risk of divorce/separation and polygyny were found to be lower among women with consanguineous marriage, while the survival of marriages was found to be higher for consanguineous marriages than for non-consanguineous marriages.

CONCLUSIONS

Findings revealed that consanguinity has some social benefits as it plays protective roles against divorce or separation, polygyny and enhances the survival of marriages.

Shared breastfeeding & other early multiple sclerosis risk factors: A case-control study

BACKGROUND

Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease. Etiology is thought to be multifactorial with genetic and environmental factors interplay. Our objective in this study is to evaluate culture specific and other early life risk factors for MS. We examined the association between MS and breastfeeding including shared breastfeeding, parental consanguinity, being born abroad or living abroad during childhood, prematurity, vaccination, tonsillectomy, rank among siblings, number of siblings, number of household members (HHM) at birth, and age first time joining school.

METHODS

This is an age and sex matched case-control study that was conducted in Riyadh, Kingdom of Saudi Arabia (KSA). We enrolled 300 cases and 601 controls. A structured questionnaire about demographics, consanguinity and potential environmental factors was answered by participants. Data was analyzed using logistic regression adjusting for covariates occurring later in life such as waterpipe smoking and performing Hajj.

RESULTS

About two thirds of the cases and the controls were females. Mean age was 34.8 (9.2) for the cases and 33.6 (10.6) for the controls. We found that shared breastfeeding (OR=0.58; 95% CI, 0.35-0.96, p = 0.033), and older age first joining school (OR=0.83; 95% CI, 0.73-0.94, p = 0.005) were associated with decrease risk of MS. While longer duration of breastfeeding by biological mother (OR=1.03; 95% CI, 1.01-1.04, p = 0.001), rank among siblings of ≥6 (OR=1.69; 95% CI, 1.11-2.56, p = 0.014), and larger number of HHM at birth (OR=2.32; 95% CI, 1.64-3.28, p = 0.001) were associated with increased risk. Patients with MS were less likely to receive formula with breastfeeding than controls (OR=0.72; 95% CI, 0.51-0.99, p = 0.046). No association was found with breastfeeding by biological mother, number of siblings, prematurity, being born abroad or living abroad during childhood, vaccination, consanguinity, or tonsillectomy.

CONCLUSION

The findings of this case-control study add to the accumulating evidence that early life factors could modify the risk of developing MS. Among these, novel associations with shared breastfeeding and number of HHM at birth are suggested. Future studies are needed to verify the observed results.

Trend in the Incidence and Prevalence of Dementia in the Faroe Islands

Background:

Dementia has become an important public health, economic, and social issue. Knowledge about prevalence, incidence, and trends of dementia in a country is of crucial importance. However, no studies of incidence or prevalence of dementia have been undertaken in the Faroe Islands.

Objectives:

The aim was to estimate the overall and trend in incidence and prevalence of dementia among individuals ≥60 years in the Faroe Islands from 2010-2017.

Methods:

Population-based register study where all individuals ≥60 years with a dementia diagnosis from January 2010 to December 2017 were identified. The overall crude and age-and-sex-specific incidence and prevalence was assessed.

Results:

The overall crude incidence among individuals ≥60 years from 2010 to 2017 was 5.1 per 1000 individuals and the prevalence 22.5 per 1000 individuals. The age-and sex-standardized annual incidence of dementia fluctuated between 4.8 and 6.7 per 1000, with no clear secular trend while the age-and sex-standardized prevalence increased steadily from 14.5 in 2010 to 30.8 per 1000 individuals in 2017.

Conclusion:

The age-standardized incidence or prevalence estimates in the Faroes seem to be lower than in other countries. The incidence was relatively stable in the period while the prevalence of dementia simultaneously increased.

High Prevalence of Dystonia in the Faroe Islands: A Population-Based Study

BACKGROUND

There are fewer than 5 population-based studies of dystonia worldwide. Only one utilized a movement disorders neurologist. Given the potential for founder effects, and the highly genetic nature of dystonia, the Faroe Islands provide a particularly interesting setting to study the prevalence of dystonia.

OBJECTIVE

To estimate the prevalence of dystonia.

METHODS

We used a 2-phase, population-based design, screening 1,334 randomly selected Faroese individuals aged ≥40 years from which a subsample of 227 participated in an in-person clinical evaluation. Dystonia was assessed by 2 movement disorder neurologists using videotaped examinations.

RESULTS

Two of 227 (0.88%, 95% CI -0.33 to 2.09%) were diagnosed with cervical or segmental dystonia. An unusual form of thumb flexion dystonia was noted in 75 more, yielding a combined prevalence of 33.92% (95% CI 27.73-40.11%).

CONCLUSIONS

The prevalence of cervical or segmental dystonia was as high as in one prior population-based study using similar methods. Furthermore, an unusual form of thumb flexion dystonia was uncovered, which yielded an extraordinarily high prevalence of dystonia in this population. Although our methods likely contributed to more complete capture of subtle dystonia, founder effects are highly likely to have been an additional major contributor to these findings.

Involuntary Thumb Flexion on Neurological Examination: An Unusual Form of Upper Limb Dystonia in the Faroe Islands

Background

The prevalence of dystonia varies worldwide. A prior report suggested a high prevalence of focal dystonia in the Faroese population, possibly reflecting a founder effect. During standardized neurological examination as part of an ongoing neuroepidemiologic study in the Faroe Islands, we noted an unusual phenomenon of thumb flexion during repetitive hand movements in a subset of subjects and sought to define its phenomenology.

Methods

We requested commentary from a panel of dystonia experts regarding the phenomenology of the movements. These experts reviewed the videotaped neurological examination.

Results

Among the experts, dystonia was the leading diagnosis. Alternate causes were considered, but deemed less likely.

Discussion

Diagnosis of dystonia requires careful clinical assessment and consideration of associated features. We report a novel form of dystonia, not previously described to our knowledge, in this isolated population. Further studies of dystonia prevalence in the Faroe Islands are merited to characterize its burden in this population and its specific clinical characteristics.

Tremor in normal adults: A population-based study of 1158 adults in the Faroe Islands

There are virtually no population-based data on tremor in normal individuals. Using a population-based sample of 1158 normal adults ages 40-98 years in the Faroe Islands, we characterized the extent of normal action tremor across age and gender strata. Participants drew two Archimedes spirals with each hand, and tremor was systematically quantified by a senior movement disorder neurologist using a reliable and valid ordinal rating scale (ratings = 0-3). Tremor was nearly universal - 1145 (98.9%) participants had a total mean spiral score > 0. Older age was associated with more tremor (p < .001) and spiral scores were higher in males than females (p < .001). The proportion of individuals with a spiral rating ≥ 1.5 (i.e., more than mild tremor) was low (1.8% - 8.5%); however, this value reached 19.6% in left-hand spirals of males ≥70 years old. In this population-based study of more than one thousand normal adults, the vast bulk (i.e., 98.9%) had tremor on spiral drawing. In general, the tremor was mild. The proportion of individuals with tremor above the mild range varied across age and gender strata. These extensive data may be used as a gold standard for defining normal levels of tremor within adult populations.

Prevalence of Essential Tremor in the Faroe Islands: A Population-Based Study

BACKGROUND

No studies of the prevalence of one of the most common movement disorders, essential tremor (ET), have been undertaken in the Faroe Islands. Given the potential for founder effects in the Islands, and the highly genetic nature of ET, the Faroe Islands provide a particularly interesting setting in which to study the prevalence of ET.

OBJECTIVE

To estimate the prevalence of ET and study its characteristics.

METHODS

We used a 2-phase, population-based design, screening 1,328 randomly selected Faroese individuals aged ≥40 years. A subsample of 282 individuals who had returned the spirals and questionnaire was selected to participate in an in-person clinical evaluation. Tremor was systematically quantified by a senior movement disorder neurologist with particular specialization in tremor using a reliable and valid clinical rating scale followed by the application of rigorous diagnostic criteria used by tremor investigators internationally.

RESULTS

The overall crude prevalence was 2.9%. The age-adjusted prevalence was 3.1%. There was an age-associated rise in prevalence; by age ≥70, prevalence reached 4.8%. Twenty six of 27 (96.2%) were previously undiagnosed.

CONCLUSIONS

This is the first population-based study of the prevalence of ET in the Faroe Islands. The estimated prevalence was similar to studies using the same or comparable methodologies.

Consanguinity: A blessing or menace at population level?

Consanguinity has highly complex and multifaceted aspects with sociocultural as well as biological debates on its pros and cons. The biological upshot of consanguinity includes the increased homozygosity, which results in manifold increased risk of genetic disorders at family and population levels. On the other hand, in addition to social, cultural, political, and economic benefits, consanguineous marriages have biological advantages at the population level. The consequence of consanguineous marriages is an upsurge in the number of homozygous diseased individuals with fewer chances of mating and reduced chances of survival, therefore evolutionarily confining the transmission of disease alleles to future generations and encouraging its elimination from a population. Protective effects of consanguinity have also been observed in a few diseases in different populations. Although attractive for many reasons, nonconsanguineous marriages will cause risk alleles to spread throughout the population, making most individuals carriers, and ultimately will resume the production of recessive diseases in subsequent generations. Although consanguinity, from an evolutionary point of view, is beneficial at the population level, it increases the risk of diseases in the very next generation. Presently, there is no treatment for most of the genetic disorders; we cannot opt for consanguinity for long-term benefits. Nonconsanguineous marriages are a better strategy by which we may delay disease manifestation for some generations until science offers a viable solution.

Both rare and common genetic variants contribute to autism in the Faroe Islands

The number of genes associated with autism is increasing, but few studies have been performed on epidemiological cohorts and in isolated populations. Here, we investigated 357 individuals from the Faroe Islands including 36 individuals with autism, 136 of their relatives and 185 non-autism controls. Data from SNP array and whole exome sequencing revealed that individuals with autism had a higher burden of rare exonic copy-number variants altering autism associated genes (deletions (p = 0.0352) or duplications (p = 0.0352)), higher inbreeding status (p = 0.023) and a higher load of rare homozygous deleterious variants (p = 0.011) compared to controls. Our analysis supports the role of several genes/loci associated with autism (e.g., NRXN1, ADNP, 22q11 deletion) and identified new truncating (e.g., GRIK2, ROBO1, NINL, and IMMP2L) or recessive deleterious variants (e.g., KIRREL3 and CNTNAP2) affecting autism-associated genes. It also revealed three genes involved in synaptic plasticity, RIMS4, KALRN, and PLA2G4A, carrying de novo deleterious variants in individuals with autism without intellectual disability. In summary, our analysis provides a better understanding of the genetic architecture of autism in isolated populations by highlighting the role of both common and rare gene variants and pointing at new autism-risk genes. It also indicates that more knowledge about how multiple genetic hits affect neuronal function will be necessary to fully understand the genetic architecture of autism.

Runs of homozygosity: windows into population history and trait architecture

Long runs of homozygosity (ROH) arise when identical haplotypes are inherited from each parent and thus a long tract of genotypes is homozygous. Cousin marriage or inbreeding gives rise to such autozygosity; however, genome-wide data reveal that ROH are universally common in human genomes even among outbred individuals. The number and length of ROH reflect individual demographic history, while the homozygosity burden can be used to investigate the genetic architecture of complex disease. We discuss how to identify ROH in genome-wide microarray and sequence data, their distribution in human populations and their application to the understanding of inbreeding depression and disease risk.

Prevalence of multiple sclerosis in Latin America and its relationship with European migration

Multiple sclerosis (MS) is a chronic, degenerative autoimmune inflammatory disease of the central nervous system. The prevalence is different in every continent, changing according to geographical and environmental characteristics. The areas with the highest prevalence in the world are Europe and North America. In Latin America, the prevalence is higher in areas where there was greater European migration, as in the case of Argentina, Chile, Brazil, Uruguay and Mexico, and there have been no identified cases amongst native Indian populations. It should be considered that environmental factors may influence the prevalence of MS in Latin America, and it seems as if there are protective factors such as exposure to ultraviolet radiation and the presence of parasitosis.

Consanguinity and multiple sclerosis susceptibility: A case control study

BACKGROUND

Several lines of evidence point towards the importance of genetic risk factors in the susceptibility to multiple sclerosis (MS). We aimed to compare the rates of consanguineous marriages between first cousins among parents of MS patients and a healthy unrelated control group.

METHOD

This study is a cross-sectional hospital registry based study, which was performed by analyzing the clinical records of patients registered with the Kashani hospital database, and also a control group of randomly selected healthy individuals.

RESULT

MS patients were significantly less an offspring of a consanguineous union than the control group (MS patients=26.1%, vs Control=32.7%, p=0.03; OR=0.730 95%CI: 0.55-0.97) CONCLUSION: Offspring of consanguineous unions seems to have a lower risk of MS compared to offspring of unrelated parents. This may have implications for inheritance mode of protective alleles in MS.

Genetic analysis of the isolated Faroe Islands reveals SORCS3 as a potential multiple sclerosis risk gene

Background:

In search of the missing heritability in multiple sclerosis (MS), additional approaches adding to the genetic discoveries of large genome-wide association studies are warranted.

Objective:

The objective of this research paper is to search for rare genetic MS risk variants in the genetically homogenous population of the isolated Faroe Islands.

Methods:

Twenty-nine Faroese MS cases and 28 controls were genotyped with the HumanOmniExpressExome-chip. The individuals make up 1596 pair-combinations in which we searched for identical-by-descent shared segments using the PLINK-program.

Results:

A segment spanning 63 SNPs with excess case-case-pair sharing was identified (0.00173 < p > 0.00212). A haplotype consisting of 42 of the 63 identified SNPs which spanned the entire the Sortilin-related vacuolar protein sorting 10 domain containing receptor 3 ( SORCS3) gene had a carrier frequency of 0.34 in cases but was not present in any controls ( p = 0.0008).

Conclusion:

This study revealed an oversharing in case-case-pairs of a segment spanning 63 SNPs and the entire SORCS3. While not previously associated with MS, SORCS3 appears to be important in neuronal plasticity through its binding of neurotrophin factors and involvement in glutamate homeostasis. Although additional work is needed to scrutinise the genetic effect of the SORCS3-covering haplotype, this study suggests that SORCS3 may also be important in MS pathogenesis.