Genetic Components and Hepatitis Risks in HS

Jeffrey Cohen, MD, is a board-certified medical dermatologist at the Yale School of Medicine in New Haven, CT. His current research focuses on the epidemiology of skin conditions, relationships between skin disorders and other medical problems, and the way that dermatologic care is delivered. He authored more than 65 peer-reviewed articles on psoriasis and other topics in dermatology. Dr Cohen joined The Dermatologist for an interview on his recent study, “Hepatitis B and C Among Patients With Hidradenitis Suppurativa: A Population-based Study.”¹

Transcript:

The study noted that these controlled analysis groups had a focus on individuals with Arab ancestry with HBV and HCV. What research is needed to determine if HBV and HCV is linked to HS in other ancestral groups?
Whenever we do these epidemiologic studies where we use a large population, we have to think at the outset about what factors could be influencing what we're trying to look at. When we're trying to ask if HS is associated with hepatitis B or hepatitis C, we need to, at the outset, try to predict what other things may influence someone's risk of having HBV or HCV.

If some other factor about an individual would increase the odds of HBV or HCV, and then we do an analysis like this and we don't think about it ahead of time, we may just be finding the effect of something that is not what we're actually trying to study. We call those, in epidemiology, covariates.

Any time we're studying any population, whether it's in Israel, or the United States, or anywhere else, we have to think about what the makeup of that population is.

In Israel, there are two main ethnic groups there. There are people who are of Jewish descent and people who are of Arab descent. In our study, it was 85% Jews and about 15% people of Arab descent. That is reflective of the population in Israel generally.

What we did find was that when we were looking at what we call independent risk factors what of those underlying things are associated with the outcome regardless of what we're actually trying to study, which was HS we found that for HBV, those of Arab descent had about a 3.8-fold increased odds of having it.

The importance of that is a couple of things. The first thing is it's important background for understanding how to interpret the results of our study, because what that tells us is that these two groups were not exactly the same in terms of their underlying propensity for the outcome to be present. Then it also helps us to understand that there is probably some genetic component here.

When we look at a lot of these epidemiologic studies, we're trying to think about which genetic components maybe are underlying, and then what we're really studying is other environmental components comorbidities, things that people are exposed to that might influence the risk of having some health condition.

For example, does having HS as your exposure increase your odds of having HBV or HCV as your outcome? We have to think about that, because we're trying to understand what other factors may be at play.

That's why we look at this, because clearly in this case, there's some difference between these groups at the outset, and presumably, there may be some genetic difference between those two groups that may underlie this.

That's something that we think might be the case, but we can't prove in any way based on the study. It's just an important observation for people to have when they are trying to understand how to interpret our results.

The study also mentions both control groups had a history of drug and/or alcohol abuse. How do these affect the HCV and HBV results?
Similar to the underlying ancestry issue, when we look at other risk factors, we know that HBV and HCV are more common in individuals who use intravenous drugs, because these are both infections that are passed on through the blood.

The main ways of getting these are through intravenous drug use. In the past, before we knew to check for it, people got it through contaminated blood transfusions. They can also be spread at the time of birth if the mother is HBV or HCV positive.

We needed to control for that in our study, and we found that, particularly for hepatitis C, these are very strong, independent risk factors, also hepatitis B, because we know that that's a way of getting it. It was very important for us to control for that in our study because we wouldn't want to be thinking that hidradenitis suppurativa was the cause of the increase in risk. We should know that this is also an issue.

When we control for it, then when we get the result that shows that HS is associated with HBV and HCV, we know that since we've controlled for it, that's not reflective of an increased risk because of drug abuse, for example.

We know that we've accounted for that in our model, and so we're really looking at what hepatitis risk is in association with HS.

 
Reference
1. Cohen JM, Kridin KK, Perez-Chada LM, Merola JF, Cohen AD. Hepatitis B and C among patients with hidradenitis suppurativa: a population-based study. Int J Dermatol. Published online May 17, 2021. doi:10.1111/ijd.15578