MS risk – Prof G's MS Blog Archive

Barts-MS rose-tinted-odometer ★ ★ ★ ★ ★

Yawn! I am getting tired of the saying the same-old things on this blog. Is it time to retire and do something new?

We have done some modelling work and predict that ~20% of new or incident cases of MS could be prevented if we stop the population from smoking. The question is how do we achieve this? Taxation has worked to some extent in that we are seeing a fall in the number of current smokers, but the numbers of teenagers smoking looks as if it is quite resistant to change. The solution must be education, education, education and a war against the tobacco industry.

If social media is such a powerful tool to hack the brains of voters, why don’t public health departments use this technology to promote their agenda? What we need are companies like Cambridge Analytica to do some good in the world and to promote a ‘Don’t Start Smoking’ campaign.

We did try and get some insights into why teenage girls start smoking when Amy Sankey, a work experience student, did a survey in her school for us. Despite the almost universal awareness of the harms of smoking in terms of lung cancer, most girls, however, did not know that there is a link between smoking and autoimmunity. I suspect even if they knew about the link it would be unlikely to prevent them from starting to smoke.

We are interested in smoking as a risk factor for MS as it is telling us something about the cause of the disease. It appears that smoking must be acting via the lungs and is due to tobacco itself. Use of oral, non-smoked, tobacco is in fact associated with a reduced risk of getting MS, hence it is not tobacco exposure. Solvent exposure is also associated with an increased risk of getting MS, which supports the lung hypothesis of developing MS.

Lung hypothesis #1 argues that damage to the lung from smoking or solvents creates a pro-inflammatory environment that is sufficient to activate pre-existing autoreactive T-cells. In comparison, lung hypothesis #2 argues that smoking damages proteins by a process called post-translational modification and that these proteins stimulate an immune response that then cross-reacts with normal antigens to set-up autoimmunity. The argument for the latter in triggering rheumatoid arthritis, an autoimmune disease of joints, is quite compelling but is less compelling when it comes to MS. We hope to study whether post-translational modification of CNS antigens is relevant in MS via an ECTRIMS fellowship we have supported.

What is interesting is that smoking interacts with genetic risk factors for developing MS and with EBV infection suggesting that there is a critical gene-environment interaction that causes MS. Wouldn’t it be interesting to study and find out what these interactions are? We have an exceptionally bright and able young researcher, Ben Jacobs, who wants to do a PhD on this exact topic; gene-environment interactions. At the moment we are ruminating about the best approach he should take to address this question. It is not an easy experiment so if you have suggestions please feel free to contact us.

I would also like to remind you that smokers who have MS have a much poorer prognosis, which is why we recommend that you stop smoking if you can.

If you are interested in smoking and MS there is a new review that has just come out.

Rosso & Chitnis. Association Between Cigarette Smoking and Multiple Sclerosis: A Review. JAMA Neurol. 2019 Dec 16. doi: 10.1001/jamaneurol.2019.4271

IMPORTANCE: Cigarette smoking is a common environmental exposure and addiction, which has severe health consequences. Smoking is a risk factor for multiple sclerosis (MS); also, smoking has been associated with disease activity and overall prognosis for patients with MS.

OBSERVATIONS: Cigarette smoking is an irritative agent on the lungs, in which a proinflammatory cascade starts that culminates in autoimmunity. Inflammation may increase the risk of MS in some individuals, in a process driven by antigen cross-reactivity between lung antigens and myelin antigens. Genetics plays a central role in the individual predisposition to mounting an autoimmune reaction. Also, free radicals, cyanates, and carbon monoxide in cigarette smoke may be directly toxic to neurons. Patients with MS who smoke have higher rates of disease activity, faster rates of brain atrophy, and a greater disability burden. Some of the outcomes of smoking were found to be reversible, which makes counselling key.

CONCLUSIONS AND RELEVANCE: The pathways involved in cigarette smoking should be further analyzed to understand the mechanisms whereby smoking worsens MS prognosis. The proinflammatory and neurotoxic outcomes of cigarette smoking may be shared by other environmental exposures, such as pollution and organic solvents. From a global perspective, efforts should be made to diminish the prevalence of cigarette smoking in patients with MS.

CoI: multiple

I have always wondered why the genomic experts in the field of MS haven’t been able to sort out why specific human leukocyte antigen (HLA) subtypes increase your risk of getting MS and others don’t.

HLA or human leukocyte antigens are the so-called signposting proteins that antigen presenting cells (APCs) use to communicate with T-cells. The APCs continuously sample the environment and present small peptides in their HLA molecules to T-cells. The HLA molecules interact with the so-called T-cell receptor (TCR) and if the peptide (message) that has been loaded in the HLA groove (signpost) and TCR, which acts as a molecular reader, fit perfectly it tells the T-cell that it should go on the attack. In the context of MS, this attack is considered to autoimmune or dysfunctional and against a self-peptide. However, the attack could be entirely appropriate and targeted against a foreign protein or a self-protein that has been altered by a process called post-translational modification. Interestingly, smoking and solvents, exposure to which are both risk factors for developing MS, are two environmental exposures that are known to cause post-translational modifications of proteins.

The following YouTube animation shows you an example of how a TCR (reader) interacts with a specific HLA molecule (signpost) and the peptide (message) in the groove of a specific HLA molecule. By watching this video you may appreciate how specific this interaction really is.

The most important genetic risk factor for deevloping MS is the so-called HLA-DRB1*15:01 molecules. If you have one copy of this gene your risk of getting MS is ~3X greater than someone without this gene. If you have two copies your risk of getting MS is about ~6X greater. In other words from a genetic perspective, you don’t want to have the HLA-DRB1*15:01 signposts.

It turns out that there, not all HLA-DRB1*15:01 molecules are made equal and that if you have the African variety, compared to the European variety, your risk of getting MS is 3x lower. Interestingly, the African and European varieties of the HLA-DRB1*15:01 genes differ in their sequence in a way that would affect the so-called peptide binding groove of the HLA molecule. This would mean that they would bind peptides differently and hence affect the way that T-cells may or may not be activated. How interesting?

The African variety of HLA-DRB1*15:01 is presumably older and the genetic change in HLA-DRB1*15:01 that is now known as the European variant must have been selected for after man left Africa and migrated into Europe. The most likely evolutionary selection pressure for this selection was repeated exposure to an infection, which selected for this variant, with the later consequence of being an increased risk of getting MS.

What is the significance of these findings? It is telling us that MS risk is related to a very specific HLA-DRB1*15:01 variant and this variant, by definition, must be interacting with a specific family of peptides or possibly a single peptide in our environment or body. Wouldn’t it be great if we could find this peptide or family of peptides? It could potentially lead us to the cause of MS.

It is important to realise that the HLA-DRB1*15:01 association with MS, and these new findings in relation to the African and European variants, is telling us that the T-cell must be the central player, or conductor, in the pathogenesis of MS and must be upstream of the B-cell. I have mulled over this for many years and I can’t think of another way of interpreting these results. Do you agree?

Chic et al. Admixture mapping reveals evidence of differential multiple sclerosis risk by genetic ancestry. PLoS Genet. 2019 Jan 17;15(1):e1007808. doi: 10.1371/journal.pgen.1007808.

Multiple sclerosis (MS) is an autoimmune disease with high prevalence among populations of northern European ancestry. Past studies have shown that exposure to ultraviolet radiation could explain the difference in MS prevalence across the globe. In this study, we investigate whether the difference in MS prevalence could be explained by European genetic risk factors. We characterized the ancestry of MS-associated alleles using RFMix, a conditional random field parameterized by random forests, to estimate their local ancestry in the largest assembled admixed population to date, with 3,692 African Americans, 4,915 Asian Americans, and 3,777 Hispanics. The majority of MS-associated human leukocyte antigen (HLA) alleles, including the prominent HLA-DRB1*15:01 risk allele, exhibited cosmopolitan ancestry. Ancestry-specific MS-associated HLA alleles were also identified. Analysis of the HLA-DRB1*15:01 risk allele in African Americans revealed that alleles on the European haplotype conferred three times the disease risk compared to those on the African haplotype. Furthermore, we found evidence that the European and African HLA-DRB1*15:01 alleles exhibit single nucleotide polymorphism (SNP) differences in regions encoding the HLA-DRB1 antigen-binding heterodimer. Additional evidence for increased risk of MS conferred by the European haplotype were found for HLA-B*07:02 and HLA-A*03:01 in African Americans. Most of the 200 non-HLA MS SNPs previously established in European populations were not significantly associated with MS in admixed populations, nor were they ancestrally more European in cases compared to controls. Lastly, a genome-wide search of association between European ancestry and MS revealed a region of interest close to the ZNF596 gene on chromosome 8 in Hispanics; cases had a significantly higher proportion of European ancestry compared to controls. In conclusion, our study established that the genetic ancestry of MS-associated alleles is complex and implicated that difference in MS prevalence could be explained by the ancestry of MS-associated alleles.

Tag: MS risk

To smoke or not to smoke that is the question

To T or not to T

Chic et al. Admixture mapping reveals evidence of differential multiple sclerosis risk by genetic ancestry. PLoS Genet. 2019 Jan 17;15(1):e1007808. doi: 10.1371/journal.pgen.1007808.