Dr. Pui Lee: I think this follows up to the discussion about symptomatic carriers. Right. Where maybe we know that one genetic variant, ADA2 is probably not sufficient by itself. Right to cause a disease. And so that's why most carriers should be, in my mind, healthy. So is there another gene that worked together in ADA2 in the same pathway where we're not finding, you know, we're not knowing much about that gene, but somewhere in that gene that together causes a phenotype? Totally possible. We haven't seen enough pattern to be able to tell. And this would take a lot of genetic analysis from lots of carriers, those with symptoms, particularly when you're comparing those without symptoms. So this will be ongoing. I think this is an excellent idea.

Dr. Pui Lee: It depends, I think. So the first is which biologic they are on. For Enbrel, Etanercept usually we don't have what we call neutralizing antibodies. That means that the body may make some antibody against the drug, but usually it doesn't interfere with its function. From the experience of treating kids with juvenile arthritis, we don't even really check for these antibodies for Etanercept. Not to say that they're absent, but they're typically don't break through in terms of their effects. But for the monoclonal antibodies like Humira adalimumab, infliximab and golimumab - those do have a risk with antibodies that are neutralizing. And those are the ones that we typically screen for and Methotrexate will reduce this risk. But the reduction of risk in this disease is also not entirely clear. It's really a risk and benefit of starting a medicine at a low dose, though methotrexate at the low dose probably would not have significant adverse effects to decrease that risk. But time will tell about how effective this approach is. But I would still screen for antibodies, even on methotrexate.

Dr. Pui Lee: The best evidence we have is the consensus paper. If you show them under box 5.1, it's a clear statement that TNF is the preferred first line treatment. And that's been working for insurance companies in the US. We don't have the level of data to get FDA approval. They require randomized trials to compare TNF inhibitors versus a placebo. For one, we need a lot more people to be able to do this. And second, it is an unethical trial. You cannot watch a group that don't get this treatment for years and years and see what happens to them.

Dr. Pui Lee: Each cohort of patients have their own longitudinal data about how many events over how many months, or per patient treated with these medicines. And the signals should be very, very small. I think these events are rare. Usually these events occur because of a couple reason, mostly because either the patients are not getting it- either not taking it, not getting enough of it, or they have developed some type of an antibody or some reason where they're not responding to it. And I think if they're on a medication and if we monitor labs for inflammation- if the CRP, for example, C-reactive protein, which is a marker that we can track for inflammation, if that is appropriately controlled, we don't see markers of systemic inflammation on TNF inhibitors. I think the risk of having a stroke or a risk of relapse is very, very low. I would say. It's probably the point where we have very few known cases of this happening. When the events happen, it's usually patients come off medicine for various reasons or the dose we give is not sufficient. I usually dose a little bit higher compared to patients with arthritis and even older children, I give an adult dose for example, if I can get approval, and checking antibodies ahead of it. I think that sometimes, just like in arthritis, some patients don't respond so well to one TNF inhibitor, like Etanercept, and we had to switch over to Adalimumab. So that happens. You know, everyone has a different response to each medicine. And that's in general medicine, too. So finding the right medicine, finding the right dose, I think will help reduce this chance to very, very, very small.

Dr. Pui Lee: Is there a way? Maybe. Would I try it? Probably not. I think that's the realistic answer because if you go back on the same drug, and it's ineffective, you won't know until the symptoms show up. And I think if you're talking about treatment of rheumatoid arthritis where your joints flare and maybe yeah, if that's tolerable. But if you talk about DADA2 where stroke is a risk on hand, I would not go back to try the same drug. Immune systems have memory. So when they start making antibodies to the drug, often that can last for quite a while even if you could sort of skip the exposure for some time. The same concept for antibiotics, where you have some people have reaction to different antibiotics. Many years later, they can still have that. So I would not I would not take that chance personally.

DADA2 Foundation: If you go to our website, you can explore what we call the DADA2 human interactive graphic. It will show you all the different areas of the body affected by the disease. Click on an area and it will list the signs and symptoms for that particular organ system. And it even then gives you a lay description of what that is beyond the medical jargon. It's an interactive tool and it pretty extensively covers almost all the signs and symptoms from the published literature.

Dr. Pui Lee: IVIg or intravenous immunoglobulin is replacement of antibodies. I think the role in DADA2 is mainly if you have a lot of infections, it's not going to change inflammation very much. We do use it in rheumatology to treat lots of different inflammatory conditions. And for this disease in my opinion, at least, I don't think it will work in terms of suppressing the vasculitis and inflammatory phenotype. Where it comes in is some patients have low white cell count and they don't make as many antibodies. And so that predisposes them to infections. Replacing with IVIg is very appropriate, I think, and even some with borderline level IVIg, they're not very low, but they get a lot of infections. IVIg is still fairly benign to help prevent infections. The vast majority of patients, particularly those with a vasculitis inflammation phenotype, don't get recurrent infections. Actually, even with TNF inhibitors they do quite well. So for most people I don't think this is needed. But in the subset of patients where infection is a concern I would certainly consider IVIg. There is also some discussion in the past that IVIg preparations contain ADA2. That is true with some preparations. IVIg is antibodies pulled together from thousands of donors and in the process of making it, ADA2 do bind to some antibodies. And so in some preparations from some companies, it comes along. But it's not always available. And then the amount you get is very small. So I don't think that's going to be the solution for DADA2 treatment.

Dr. Pui Lee: The answer from my lab, actually, we have done quite a bit of work on this answer is no. The ADA2 level primarily is driven by the particular variant that you have, some variants affect a function more, and those individuals will have lower levels in the carrier range. And then, the variants that don't affect function very much, those people would have, higher levels in the carrier range. It's also difficult to really define what symptoms do we call symptomatic carriers. I showed you that the graph of so many different symptoms that you can have of DADA2. Which one of those are we going to say they are symptomatic carrier versus like a migraine headache, which a lot of people have in general? Is that really the DADA2 carrier phenotype or is it just population, general phenotype? There's some difficulty there. But the people that come to me with this carrier question, we have measured their level. I don't think the level has been any different from those that do not ask me this question.

Dr. Pui Lee: There is an understanding here that these phenotypes, when we talk about the inflammation versus hematologic, these are not completely mutually exclusive things. And so you can have both. And I know many people actually have both. I tried to simplify things a little bit and say Enbrel and the equivalent are effective on inflammation. We also know that this kind of medicine doesn't really fix the bone marrow picture. It doesn't make it worse, but it won't really make a neutrophil count come up. It won't make the anemia go away, unless it’s part of inflammation. There are people that have some of these inflammatory features and the blood issue. So that medicine will only give you sort of a partial improvement, partial benefit. But I think it is a smaller subset. I would say probably about 10 to 20% are the patients that have these mostly primarily hematologic issues. Not all require transplant. I think that's another message here. Right? I think we talked about that as sort of the ultimate solution. But many patients have low white blood cell count that doesn't really functionally impair their lifestyle. If you're not getting infections, even if white blood cell count is low, it doesn't mean that you got a ton of infections every month. And if your red blood cell count is just a little bit low and not very anemic, that you need transfusion for. Maybe you don't need to do anything about it? And so, the science is not perfect, right. The dividing people into different groups. It makes it easier to discuss treatment, to get approval and think about, you know, who's the right candidate for transplant. But there's definitely overlap and not one treatment works for everyone, I think.

Dr. Pui Lee: Dr. Isabelle Meyts and Dr. Hassan Hashem, they're the transplanters that work on this. So the last paper showed about 30 individuals, and, and the survival rate was really good. I don't recall there's any death in that particular paper. But in a community, Dr. Chambers knows that there are cases that that don't go well, and I don't think we've fully captures that yet. I don't think the risk is particularly higher for DADA2 compared to any other disease that we transplant for, which is setting the bar somewhere around that 5 to 10% range. *NOTE: Dr. Meyts and team are currently working on updating that paper with more data.

Dr. Pui Lee: No solid data to make this correlation. I do have a couple patients where growth early on has been an issue for them. And I do wonder whether there's some level of chronic inflammation that affects growth. And this, again, is not a DADA2 specific type of issue. We see this with other genetic diseases that involve inflammation. And I think until they get to the right treatment, I think that level of inflammation in the body can affect lots of things. But there's also a significant level of heterogeneity for DADA2. DADA2 is quite impressive in terms of with the same disease right, how everyone can be so different. So I think a growth issue is probably related to just having chronic inflammation. I don't think it is something that's true across the board for all DADA2 patients.

Dr. Pui Lee: Lab scales vary, so single values are hard to compare; generally, no consistent correlation observed.

Dr. Pui Lee: Clinical tests are discussed in the consensus paper. I check CBC diff, ESR, CRP, complete metabolic panel, IgA/M/G at each visit, and antidrug antibody once a year if applicable.