One of my colleagues, with whom I was co-authoring an editorial on smouldering MS, demanded I delete the section on premature ageing being a factor driving delayed worsening of disability in people with MS (pwMS). I refused so we had to pull the editorial. The fact that he is quite old and doesn’t like the hypothesis of brain & cognitive reserve being neuroprotective explains his position. He criticised my theory for being ageist.
I am more convinced than ever that premature ageing is a big driver of delayed worsening in MS.
A few years ago I was asked to see a patient from the North of England who has presented in her early 60’s with SPMS. She had had three spinal cord attacks in her late teens and had been in remission until her late 50’s when she noticed increasing weakness in her weaker leg with foot drop. In the intervening 40 years since her last attack, she had been relapse-free and fully functional apart from mild persistent weakness in her one leg that prevented her from running.
As part of her work-up, I repeated her MRI of the brain and spinal cord and we performed a lumbar puncture. Her CSF showed local synthesis of oligoclonal IgG bands consistent with her diagnosis of MS and her neurofilament levels were low. Her MRI showed no active or new lesions and apart from some brain and spinal cord atrophy, there was nothing extraordinary about her imaging. When I saw her in outpatients I explained to her that she did not have active MS and that her diagnosis was now non-relapsing or inactive secondary progressive MS; I now refer to this as smouldering MS.
She then volunteered that she didn’t think her worsening was due to MS, but rather ageing. I couldn’t disagree with her and explained that her previous MS attacks had probably reduced the number of axons or nerve fibres in the motor pathway to her leg, which was now ageing as the surviving nerve fibres were gradually dying off she was seeing increasing weakness in the leg. This is called the premature ageing theory of progressive MS. Is there any proof for it?
We know from other neurological diseases that ageing can cause delayed worsening. The most well know one is post-polio syndrome. This is when people who have had polio notice increasing weakness in previously affected muscles decades later as they start to age. In HIV we see age-related neurodegenerative diseases present decades earlier than one would expect. The theory being that HIV infection of the brain reduces reserve and triggers premature ageing mechanisms. Even with Alzheimer’s disease factors that are associated with reduced brain reserve result in an earlier age of onset of dementia.
I suspect MS is not and exception and that ageing, or premature ageing, is part of the disease. The problem we have is that disease duration and disability are strongly correlated with ageing. This makes it difficult to unentangle ageing from disease duration. One way to look at this is to use biomarkers of ageing. As you get older the ends of your chromosomes or telomeres get shorter. Telomere length is used as a biomarker of physiological and not chronological ageing. By using telomere length instead of your age we may be able to unpick the impact of ageing on disease worsening.
In this study below there was a clear gradient in terms of disability and telomere length. Shorter telomere length was associated with disability independent of chronological age, suggesting that biological ageing is contributing to neurological injury in MS.
The implications of this are enormous and imply that we should be targeting age-related mechanisms as a therapeutic strategy in MS. This is why I also include ageing in my holistic management of MS talks and why focusing on all of those lifestyle issues and comorbidities is so important in MS. Interestingly, I made this a major theme in my talk at ACTRIMS last year when I had to predict what was going to happen in MS in 5 years time (slides below).
So the time for biohacking (diet) and aggressive lifestyle interventions have arrived in the MS space. The million-dollar question is how to we get the MS community to buy into this as a therapeutic strategy.
Krysko et al. Telomere Length Is Associated With Disability Progression in Multiple Sclerosis. Ann Neurol, 86 (5), 671-682 Nov 2019.
Objective: To assess whether biological aging as measured by leukocyte telomere length (LTL) is associated with clinical disability and brain volume loss in multiple sclerosis (MS).
Methods: Adults with MS/clinically isolated syndrome in the University of California, San Francisco EPIC cohort study were included. LTL was measured on DNA samples by quantitative polymerase chain reaction and expressed as telomere to somatic DNA (T/S) ratio. Expanded Disability Status Scale (EDSS) and 3-dimensional T1-weighted brain magnetic resonance imaging were performed at baseline and follow-up. Associations of baseline LTL with cross-sectional and longitudinal outcomes were assessed using simple and mixed effects linear regression models. A subset (n = 46) had LTL measured over time, and we assessed the association of LTL change with EDSS change with mixed effects models.
Results: Included were 356 women and 160 men (mean age = 43 years, median disease duration = 6 years, median EDSS = 1.5 [range = 0-7], mean T/S ratio = 0.97 [standard deviation = 0.18]). In baseline analyses adjusted for age, disease duration, and sex, for every 0.2 lower LTL, EDSS was 0.27 higher (95% confidence interval [CI] = 0.13-0.42, p < 0.001) and brain volume was 7.4mm3 lower (95% CI = 0.10-14.7, p = 0.047). In longitudinal adjusted analyses, those with lower baseline LTL had higher EDSS and lower brain volumes over time. In adjusted analysis of the subset, LTL change was associated with EDSS change over 10 years; for every 0.2 LTL decrease, EDSS was 0.34 higher (95% CI = 0.08-0.61, p = 0.012).
Interpretation: Shorter telomere length was associated with disability independent of chronological age, suggesting that biological aging may contribute to neurological injury in MS. Targeting aging-related mechanisms is a potential therapeutic strategy against MS progression. ANN NEUROL 2019;86:671-682.