I'm going to break the ice here and make the first student post because class this week got me all excited! Just this past week the lab I work in submitted an abstract about antiphospholipid antibody syndrome (APS) in children. In short, this syndrome is characterized by blood clots associated with so-called “antiphospholipid antibodies” (although, these antibodies generally don’t bind phospholipid, but rather phospholipid-binding proteins…for an excellent, in depth review see:
http://www.ncbi.nlm.nih.gov/pubmed/12871358?ordinalpos=27&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum ).
To be diagnosed with APS a person must present with a thrombosis (blood clot). They then need to have positive tests for antiphospholipid antibodies on two separate occasions that are at least three months apart. So, by definition, the people with APS consistently have these antiphospholipid antibodies, which are not usually present in normal, healthy people.
These so-called “antiphospholipid antibodies” are not necessarily directed against phospholipids - that is just the term that has been given to the population of antibodies that seem to be common in people with APS. For our discussion, it isn’t essential to understand what the antibodies are directed against because how each antibody may activate blood clotting isn’t entirely understood. For our purposes, all that needs to be understood is that these patients have abnormally high levels of autoantibody for long periods of time. This is true even when these APS patients are compared to other children who have had blood clots.
Our study focused on children who were diagnosed with APS. APS is a rather complex syndrome that is fairly common in adults with thrombosis but has been little studied in children. Our lab (which includes fellow classmates ChrisB7630 and MeghanC7630) started studying APS in children in hopes of finding a relationship between certain antiphospholipid antibodies and thrombotic outcome, with the long-term goal of using this data to improve clinical care for children affected with APS. Our findings (as presented in our abstract which follows in a comment - beware, it is quite technical!) found that, in general, children who have persistently positive (positive for at least three months) IgM antibodies are more likely to have had recurrent blood clots. After class we started to wonder if maybe the high levels of IgM themselves are responsible for recurrence, as high concentrations the big IgM molecules could make the blood "sticky". Or maybe having consistently high IgM levels is indicative of some sort of underlying inflammation that may have a role in thrombosis.
I’m very much looking forward to this class! I’m excited to see what light others can shine on our work. Yay!
8 comments:
In a Prospective Inceptional Cohort Study of Children with Thrombosis, a Persistently Positive Dilute Russell Viper Venom Time is Associated with Thrombus Progression or Recurrence and Multiple Antiphospholipid Antibodies
Hannah A Hathaway, BA, Emily L. Joachim, Linda Jacobson, MT, Chris G. Bombardier, BS, Neil A Goldenberg, MD, PhD, William E. Hathaway, MD and Marilyn J. Manco-Johnson, MD
Department of Pediatrics and Mountain States Regional Hemophilia & Thrombosis Center, University of Colorado Denver and The Children's Hospital
BACKGROUND: Antiphospholipid antibodies (APA) that persist ≥12 weeks in adults with acute thrombosis are predictive of thrombus recurrence. The significance of APA in children with thrombosis is unclear. This study was developed to examine the relationship of a persistently positive lupus anticoagulant (≥ 12 weeks), assessed by the dilute Russell Viper Venom Time (dRVVT), to adverse thrombus outcomes including progression or recurrence. In addition, the relationship of a persistently positive dRVVT to the prevalence and titer of several other APA in children with thrombosis was examined. METHODS: Data from a consented prospective inceptional cohort study of pediatric thrombosis and thrombophilia (COMIRB 05-0339) were extracted for this analytic project. Eligibility included age ≤ 21 years at presentation, objectively confirmed thrombus, dRVVT within 4 weeks of presentation and repeated ≥ 12 weeks later. Patients with a persistently positive dRVVT (ratio of Screen/Confirm ≥1.2) were classified as having antiphospholipid syndrome (APS positive), and those with a negative dRVVT were classified as APS negative. Twelve or more weeks from presentation, patient plasmas were tested in ELISA assays for the presence and titer of IgM and IgG antibodies directed against protein C (PC), protein S (PS), prothrombin (II), ß-2-Glycoprotein I (B2GPI), and cardiolipin (ACA). A euglobulin clot lysis assay (ELT) and hexagonal (II) phase phospholipid assay (STACLOT LA, Diagnostica Stago, Inc.) were also performed. RESULTS: The cohort included 122 cases with thrombosis. Of these, 35 failed eligibility due to transient dRVVT positivity or lack of blood sampling within the specified time period. Of the remaining 87 patients, 43 were APS positive and 44 were APS negative. APS positivity was associated with longer duration of therapy (p<0.001) and multiple autoantibodies at ≥ 12 weeks from presentation (p=0.04). APS was associated with higher titers of several antibodies, including those directed against: B2GPI (IgG, p=0.01), II (IgG, p=0.02), PC (IgG, p=0.03; IgM, p<0.001). Despite the longer duration of therapy for these patients, APS was highly associated with thrombus progression or recurrence (47% in APS positive versus 8% in APS negative, p=0.001). Thrombus progression or recurrence was further associated with positivity for ACA IgM, Anti-II IgM and the STACLOT LA (p=0.02 for each), and additionally with higher titers of antibodies against B2GPI (IgG, p=0.03), II (IgM, p=0.05), PC (IgM, p=0.04), and PS (IgM, p=0.03). CONCLUSION: In this pediatric prospective inceptional cohort study, APS (defined as a persistence of positive dRVVT 12 weeks or greater in children affected with thrombosis), was found in more than one third of children and was associated with higher prevalence and titers of several APA. In spite of longer duration of therapy, children with APS had a significantly higher rate of thrombus progression or recurrence. APA testing in children with thrombosis is important to predict outcomes. Future clinical trials must consider APS status in evaluating risk-stratified therapy for thrombotic diseases in children.
That is an exciting result. How could you prove the IgM is causing thrombus formation or the result of thrombus?
Well, as of now, we have not done the research to be sure of which comes first, the clot or the IgM. I know that in the adult APS population, the general opinion is that the antibodies cause the clot. Evidence that the same is true in children comes from our APS negative group - none these 44 children with thrombus were found to have the same strickingly high titer IgM levels as the children in the APS positive group. If the clot was causing the IgM, one would expect to see a higher prevelence of IgM in all children in thrombus, not just in those with APS.
Also, to answer this you could try purifying IgM from the APS patients with the high IgM and injecting it into a mouse model and see if thrombus occurs.
Hi Hannahh7630,
I'm a platelet person, so your research is especially interesting to me!
I think it could be very interesting to the U of A 495 crew as well...but it might be slightly too technical for them...I was hoping that I could talk you into telling us what you did in slightly less scientific language! This is a great skill for any of us to master...since you never know who will ask questions!
Thanks!!
ZoeC495
So the patients without APA actually have the original thrombus when you checked for IgM and they don't have elevated IgM? Does the half-life of IgM need to be considered?
My lab is working on Cerebral Cavernous Malformations (CCM). These are mulberry-like blood vessel malformations of the central nervous system that form from an over growth of vascular endothelial cells lining the blood vessels. In patients with the familial form of CCMs they may have 20 or more CCM lesions and the lesions are low flow and in each cavern one finds various stages of thrombus formation. Do you think it would be helpful to look for IgM in at least one of these patients? Since there are many stages of thrombosis in CCM lesions one would expect IgM to be present if it is required in general for thrombosis. I don't think anyone has looking into it in this disease. There are plasma B cells and oligoclonal bands present in some of the patients so there is an immune component.
ZoeC495,
I made some edits to the original post to try to make it more readable...the problem is that this syndrome has all these weird names that are misleading and confusing, but I hoped I cleaned it up a little.
Thanks!
-Hannah
This is quite interesting! Has anyone discovered what the antibodies are directed against and whether both IgG and IgM have the same variable sequencing? If IgM is mostly found in these patients I would think about finding if there’s a mutation in either the over production of these antibodies or a mutation/error in the IgM/IgG class switching.
KatherineB7630 -
That is exactly what we were thinking, especially after taking this class! It seems there must be a defect in class switching or some sort of chronic inflammatory response that is causing this long-term expression of IgM.
JudyG7630 -
The half-life of IgM definitely plays a role in this. In the set of patients we studied, all the IgM testing was performed at at least three months after their original thrombus - well beyond many half-lives of IgM. So it is not surprising that the APA negative children don't have those antibodies, but it is most striking that the APA positive children still have these IgM antibodies, even after several months.
As for the role of IgM antibodies in your CCM patients - it could be interesting to look at. It has been proposed that in order to have a clot, APS patients need a "second hit" besides the antibody - a vessel malformation would definitely meet this criteria. If you are interested a good starting point would be to beform some dRVVT testing on your patients, as this would be a much more affordable way to screen for general presence of APA.
The whole idea is very interesting as it would suggest that the vessel malformation/endothelial cell damage might be triggering the formation of APA.
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