Sep 18, 2018
Dr Carolyn Lam: Welcome to Circulation on the Run, your weekly podcast summary and backstage pass to the journal and its editors. I'm Dr Carolyn Lam, associate editor from the National Heart Center and Duke National University of Singapore. This week's journal features two papers that deal with genetic testing in young athletes and for sudden arrhythmic death, and with findings that may surprise you. They really show the complexities of this era of genetic testing and cardiovascular medicine, and in fact are discussed as growing pains in cardiovascular genetics. You must listen to our feature discussion, which is coming right up after these summaries.
The first original paper this week suggests that targeting fibronectin polymerization may be a new therapeutic strategy for treating cardiac fibrosis. Fibronectin polymerization is necessary for collagen matrix deposition and is a key contributor to increased abundance of cardiac myofibroblast following cardiac injury. In today's paper, first author Dr Valiente-Alandi, corresponding author Dr Blaxall from University of Cincinnati College of Medicine and Heart Institute, and their colleagues hypothesized that interfering with fibronectin polymerization, or its genetic ablation and fibroblasts, would attenuate myocardial fibrosis and improve cardiac function following ischemia reperfusion injury. Using mouse and human cardiac myofibroblasts, authors found that the fibronectin polymerization inhibitor pUR4 attenuated the pathological phenotype exhibited by mouse and human myofibroblasts by decreasing fibronectin polymerization and collagen deposition into the extracellular matrix as well as by myofibroblast proliferation and migration.
Inhibiting fibronectin matrix deposition by pUR4 treatment or by deleting fibronectin gene expression in cardiac fibroblasts confirmed cardioprotection against ischemia reperfusion-induced injury by attenuating at first left ventricular remodeling and cardiac fibrosis, thus preserving cardiac function. In summary, interfering with fibronectin polymerization may be a new therapeutic strategy for treating cardiac fibrosis and heart failure.
The Insulin Resistance Intervention after Stroke, or IRIS trial, demonstrated that pioglitazone reduced the risk of both cardiovascular events and diabetes in insulin-resistant patients. However, concern remains that pioglitazone may increase the risk of heart failure in susceptible individuals. To address this, Dr Young from Yale Cardiovascular Research Center and the IRIS investigators performed a secondary analysis of the IRIS trial. They found that older age, atrial fibrillation, hypertension, obesity, edema, high CRP, and smoking were risk factors for heart failure.
Pioglitazone did not increase the risk of incident heart failure, and the effect of pioglitazone did not differ across levels of baseline risk. It should however be noted that in the IRIS trial, the study drug dose could be reduced for symptoms of edema or excessive weight gain, which occurred more often in the pioglitazone arm. Overall, pioglitazone reduced the composite outcome of stroke, MI, or hospitalized heart failure in the IRIS trial.
The next study highlights the importance of genetic variation in cardiac fibrosis and suggests that while fibroblast activation is a response that parallels the extent of scar formation, proliferation may not necessarily correlate with levels of fibrosis. In this paper from co-first authors Dr Park and Ranjbarvaziri, corresponding author Dr Ardehali, from David Geffen School of Medicine, University of California, Los Angeles, the authors utilized a novel multiple-strain approach known as the Hybrid Mouse Diversity Panel to characterize the contributions of cardiac fibroblasts to the formation of isoproterenol-induced cardiac fibrosis in three strains of mice.
They found that isolated cardiac fibroblasts treated with isoproterenol exhibited strain-specific increases in the levels of activation, but showed comparable levels of proliferation. Similar results were found in vivo with fibroblast activation but not proliferation correlating with the differential levels of cardiac fibrosis after isoproterenol treatment. RNA sequencing revealed that cardiac fibroblasts from each strain exhibited unique gene expression changes in response to isoproterenol.
The authors further identified LTBP2 as a commonly upregulated gene after isoproterenol treatment. Expression of LTBP2 was elevated and specifically localized in the fibrotic regions of the myocardium after injury in mice and in human heart failure, suggesting that it may be a potential therapeutic target. That brings us to the end of our summaries. Now for our feature discussion.
We all know that t-wave inversion is common in patients with cardiomyopathy, however up to a quarter of athletes of African descent, and five percent of white athletes also have t-wave inversion on ECG, but with unclear clinical significance despite comprehensive clinical evaluation. Now, what is the role in diagnostic use of genetic testing beyond clinical evaluation when we investigate these athletes with t-wave inversion? Well we're about to get some answers in today's feature paper, and I'm so pleased to have the corresponding author of the paper, Dr Sanjay Sharma from St. George's University of London, as well as our associate editor Dr Mark Link from UT Southwestern.
Sanjay, please let us know what you did and what you found.
Dr Sanjay Sharma: Well as you rightly say, that up to 25% of black athletes have t-wave inversion, as do three to five percent of white athletes. And these t-wave inversions often overlap with the sort of patterns that you see in patients with hypertrophic cardiomyopathy and arrhythmogenic cardiomyopathy. For example, 80% of people with hypertrophic cardiomyopathy have t-wave inversion as do 60% of patients with ARVC. Now we know that some ECG patterns, t-wave inversions in V1 to V4 are benign in black patients, but the significance of other ECG patterns is unknown. Cascade screening in family members with cardiomyopathy have shown that t-wave inversion may be the only manifestation of gene inheritance, and there are reports to suggest that some athletes with t-wave inversion do go on to develop overt cardiomyopathy. Now when we investigate the vast majority of our patients with t-wave inversion, these are our athlete patients, we don't actually find anything. But over the past decade, also, these has been major advance in next generation sequencing that allows us to perform genetic testing in a large number of genes that can cause diseases, capable of causing sudden death.
And so, we thought we'd investigate the role of this gene testing in athletes with t-wave inversion. We looked at a hundred, 50 black athletes and 50 white athletes who had t-wave inversion, and we investigated them comprehensively with clinical tests. But we also added in a gene panel looking at 311 genes implicated in six cardiac diseases, notably hypertrophic cardiac myopathy, arrhythmogenic cardiomyopathy, dilated cardiomyopathy, left ventricular non-compaction, long QT syndrome, and the brugada syndrome. We found that 21% of our athletes were then diagnosed with a cardiac disorder capable of causing sudden death, and the vast majority of these people had hypertrophic cardiomyopathy. And this diagnosis was based on clinical evaluation. When we looked at gene testing, we found that gene testing only picked up a problem in 10%. So, the diagnostic yield of gene testing was half that of comprehensive clinical investigation.
When we actually looked at athletes who had nothing wrong with them in clinical investigation, and actually had a gene mutation, we found that only 2.5% of athletes who had t-wave inversion but clinically normal tests, actually had something wrong with them. And our conclusions were that gene testing picks up only half the athletes that clinical testing does, and gene testing is only responsible for identifying 2.5% of athletes with t-wave inversion, where clinical tests are negative. That was the summary of our study in short. We did find that black athletes were less likely to have a positive diagnosis of cardiac myopathy than white athletes, and black athletes are also less likely to have a genetic mutation capable of causing a cardiomyopathy than white athletes.
Dr Carolyn Lam: First and foremost, congratulations on such a beautiful paper, and so wonderfully summarized as well. It really seems to fly in the face, doesn't it? Of the way we've been discussing personalized medicine and saying that we're going to start whole genome sequencing everyone and that's going to provide all the answers for future disease risks. I mean, if I'm not wrong, what your paper is trying to tell us is that at this moment we don't have good examples where genetic testing may trump clinical diagnoses, and in fact we should be still focusing on a comprehensive clinical evaluation of patients and in the absence of a genotype we should learn to question what we're doing in genetic testing. Do you agree with that?
Dr Sanjay Sharma: You couldn't have said that more precisely. As I've said, the diagnostic yield of clinical testing was 21% versus only 10% with genetic testing. The diagnostic yield of pure genetic testing in people with otherwise completely normal findings clinically was only 2.5%. And the other thing that I forgot to tell you was that genetic testing, if we included genetic testing in addition to comprehensive assessment, cost us three times as much as clinical investigation on its own, and had we relied solely on genetics, and nothing else, it would have cost us ten times more than clinical testing. So our cost per making a diagnosis using genetics only would have amounted to $30,000 per condition.
Dr Carolyn Lam: Wow, what a great wake up call. Mark, you've thought a lot about this and in fact there was another paper in this week’s journal that has very complimentary messages. In fact you invited an editorial by Dan Roden, and I really loved his title of it, "Growing Pains in Cardiovascular Genetics." Would you maybe add your thoughts in relation to the other paper, as well as overall?
Dr Mark Link: Sure. Circulation was very interested in these papers. These are really ... Now, as Dan Roden says, "Growing pains." Twenty years ago when genetics came out it was looked upon as it was going to completely change our clinical medicine and precision medicine is really relying a lot on genetics. And while ultimately that may be the case, we are in a stage now where the honeymoon is over. And the other paper that was in this same issue was a paper by Hosseini and colleagues, and it was the Clin Gen paper looking at the Brugada Syndrome abnormalities. Now the Clin Gen is an NIH sponsored group that takes individuals from a number of different institutions and actually gene testing, and tries to provide an independent assessment of the abnormality of genes. Previously is was companies that did this. A company would gene test ... They would look for gene abnormalities, try to link it with clinical disease, and they could basically then do just on their patients. But Clin Gen now is trying to tie all those companies together to get a broad consortion and to look at genetic abnormalities and whether they're truly pathologic, where there's areas of unknown significance, or whether they're truly not pathologic.
So as an example, they took Brugada Syndrome, and they took the different gene abnormalities that have been described from basically different companies and different labs and different institutions, and they looked at the evidence behind the fact that they were truly pathologic, 'cause all 21 genes were defined as pathologic. They found in their independent assessment that only one ended up to be truly pathologic, and the others ones were disputed. And sort of another wakeup call that just because a single company calls a gene pathologic or Brugada Syndrome, does not make it pathologic necessarily. So we all thought these were two very important papers that looked at some of the limitations of genetic testing. We asked Dan Roden, who is really a very accomplished scholar in this field, to provide perspective on this. And I agree, I loved his title, "Growing Pains in Cardiovascular Genetics." And what he did is reviewed the history of genetic testing, and he actually starts before genetic testing and starts with Mendelian genetics, and [inaudible] genetics. And then 23 years ago they started linking that Mendelian genetics to gene abnormalities, especially in diseases such as long QT syndrome and hypertrophic cardiomyopathy.
We've come a tremendous way in diagnosing gene abnormalities and associating them with these underlying cardiac myopathies and hind channel abnormalities. So no one doubts we've come a tremendous way, but there's a long way to go in terms of getting better diagnostic accuracy and really defining where these genetic testing are ultimately going to play out in clinical medicine. So everyone's excited about it, but I think these two papers are two cautionary tales that we do have to remember that genetic testing in 2018 is not the end all and be all.
Dr Carolyn Lam: I love that, cautionary tales. So important. But where do we go from here? What's the take home message for clinicians listening to this today in 2018? I mean is it that perhaps when we do these things we now need to include medical geneticists and genetic counselors as vital partners as we look at this all? Perhaps we need to not forget the primacy of clinical evaluation. What do you think, Sanjay?
Dr Sanjay Shar: Well, there are guidelines from the American Medical Genetics side as to what one defines as a disease-causing mutation. But I agree that we need to be using certified laboratories that can actually interpret the genetic mutations. For example, in our study of athletes, 63% actually had variance of undetermined significance. So they had spinning mistakes in their genes which probably didn't account to anything at all, but had these mutations, or these so called variance of undetermined mutations been interpreted by someone who didn't really know much about this, these could have resulted in false positive results which could cause absolute chaos for an athletes career. So I do think this type of testing has to be governed very, very carefully and needs to be performed in very specialized and certified laboratories.
Dr Carolyn Lam: Indeed. Not just to the athlete, but to their families too, isn't it? Mark, what do you think is the take home message [inaudible 00:16:18]?
Dr Mark Link: I think one of the big take home messages that I took away from these papers is that clinical medicine is not dead. In fact, clinical medicine in this day and age is still the prime way of taking care of patients. Genetic testing is still in its infancy. It doesn't help clinically in too many situations yet. It will in the future. It helps in the diagnosis, it's not as useful in the treatment. So we have a long ways to go with genetics. I like your comment that going forward we're going to need more genetic counselors to make sense of these results. Clinicians are going to have a hard time making sense of these results. I do think that there is plenty of role once a disease causing mutation has been defined, and in that situation it's invaluable in cascade screening in identifying other family members who may be affected, but outside that I do believe and I agree completely with both of you, that clinical medicine is not dead. And clinical evaluation should be number one and should enjoy it's prime time because that's where we still are at. And genetics is still in its infancy and so is cardiology.
Dr Carolyn Lam: Perhaps in selective settings ... We're not talking here about, for example, hypercholesteremia variance, we're not talking about cancer gene variance for which screening may be a little bit more advanced, and we may understand the gene phenotype associations that are perhaps-
Dr Mark Link: I think that understanding gene phenotype associations are going to be critically important in the future. I think, as Sanjay said, the real use of genetic screening now is cascade screening for the family, and there it's invaluable. That you can tell if you've got a co-band with the disease, and with a defined pathological mutation. You can test siblings, sons and daughters, parents to see if any of them have the gene. I think that's where it should be used for sure in 2018.
Dr Carolyn Lam: Thank you so much Mark and Sanjay. So some precautions, some hope. Very, very balanced discussion. So much more we could discuss, so I really want to highly encourage our audience. Pick up this issue. You have to read these amazing papers and the editorials.
Dr Carolyn Lam: So, here's a podcast with all your colleagues, and don't forget to tune in next week.