Carl, a follower of this blog, wrote to me regarding a study that appeared in Nature; Scientific Reports, in April 2020 -- less than a year ago. It reported a study from South Korea examining a correlation between psoriasis and Alzheimer's disease. The study reviewed the cases of about a half million subjects with psoriasis vs. about 2.7 million without psoriasis. The study noted that both diseases have a genetic component, and research has recently identified genetic overlap between the two. The study looked for an overlap between expression of the diseases and the genetic overlap. In other words, if you have psoriasis, are you more likely to get Alzheimer's disease?
This is a useful question in that psoriasis usually appears at a much younger age than Alzheimer's disease. Therefore, psoriasis might be a useful predictor of Alzheimer's disease. At the very least, it might help identify subjects for study of pre-clinical Alzheimer's disease.
And then there's this: Does treating psoriasis also treat Alzheimer's disease? Good question.
So, does psoriasis increase the risk of developing Alzheimer's disease? The researchers found "a significantly increased risk of AD in Korean patients with psoriasis compared to a matched control group." After a followup of a little more than three years, 1.87% of subjects without psoriasis developed Alzheimer's disease, while 2.11% of subjects with psoriasis developed Alzheimer's disease. (These numbers can be misleading, since closer examination is required to consider medications subjects were taking, genetic differences, lifestyle differences, etc.)
What do psoriasis and Alzheimer's disease have in common? Both have a strong genetic component for their origins, although other factors (such as lifestyle) play a role. And, according to the article, the genetic overlap involves genes associated with inflammation. Inflammation plays an important role in Alzheimer's disease and in some forms of psoriasis. So, inflammation seems to be the linking factor. The study noted, "These results indicate that chronic inflammatory conditions in psoriasis may have an important impact on the nervous system and thus in increasing the risk of developing Alzheimer's disease."
As with Alzheimer's disease, there is no cure for psoriasis, but there are treatments. Some of these target inflammation. The study reviewed several of the treatments to see if the treatments also affected Alzheimer's disease. The study found "a significant reduction in the incidence of Alzheimer's disease among patients with psoriasis prescribed systemic medications (acitretin, methotrexate, cyclosporine, and biologic agents) compared to controls without psoriasis." One drug (acitretin), also appeared to suppress the production of beta amyloid by a separate mechanism. Unfortunately, these tend to be aggressive medications with substantial side effects.
Recall that in April 2019 we reported on research finding that anti-inflammatory medications, at least non-steroidal anti-inflammatory drugs like naproxen and aspirin, did not help Alzheimer's patients. Is this an inconsistency?
Another question worth considering: Could treatments for other inflammatory skin disorders also be effective against Alzheimer's disease?
As with pretty much every study I read, they closed with "Further studies are needed..."
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