Access an abstract of this month’s featured research article: Evidence-based path to newborn screening for duchenne muscular dystrophy. Ann Neurol. 2012 Mar;71(3):304-13.
Kevin Flanigan: Welcome to This Month in Muscular Dystrophy. I'm Kevin Flanigan from the Center for Gene Therapy at Nationwide Children's Hospital in Columbus, Ohio. Each month on this podcast we invite authors of recent publications to discuss how their work improves our understanding of inherited neuromuscular diseases and what their work might mean for treatment of these diseases.
Today, it's my pleasure to have back again as our guest, Dr. Jerry Mendell, MD, current peter's chair of Pediatrics and professor of Pediatrics and Neurology and Pathology at the Ohio State University and director of the Center for Gene Therapy here at Nationwide Children's Hospital.
Jerry Mendell: Thank you.
Kevin Flanigan: Well it's a pleasure to talk to you about this brand new paper. A reminder to our listeners that there's a link to this paper's abstract on our Nationwide Children's website. The title of the paper is Evidence-based Path to Newborn Screening for Duchenne Muscular Dystrophy.
Let's begin with newborn screening. What is newborn screening and how is it done?
Jerry Mendell: Newborn screening is a method of identifying genetic defects at birth that are commonly encountered in the population. Examples are cystic fibrosis that may be one of the newer ones if we go back to the history of newborn screening, phenylketonuria was initially introduced.
Newborn screening was implemented so that babies at the time of birth could be treated as soon as possible rather than waiting till five, six, seven years old and having the disease diagnosed at the time and having the condition gone so far that little treatment could be offered to the children.
Kevin Flanigan: So newborn screening, it's been around for decades and it's mandated by law in every state, isn't it correct?
Jerry Mendell: Yes. And Ohio is very conscientious about newborn screening. In fact, it is a state-by-state organization for newborn screening. Each state actually decides how many newborn screens they actually want and in Ohio we have 35 screens for newborn diseases. It's one of the highest in all the states in the country.
Kevin Flanigan: So that screening, itself, is actually done off a blood spot that's put on to a card, isn't that correct? Many of our listeners, parents will remember that being done to their infants at the time of birth.
Jerry Mendell: Right. Sometime within the first 24 to 48 hours, the baby's heel is pricked with a needle, blood spots are obtained on a card and from this card the analysis of the specific test is done. They're done in various ways, some are biochemical analysis and others are DNA analysis.
Kevin Flanigan: So how do you use one screen for muscular dystrophy from a blood spot? How did you go about doing this?
Jerry Mendell: Screening for muscular dystrophy is a challenge actually, because we have Duchenne muscular dystrophy, which is our target disease, is caused by a gene, which is the largest gene in the human genome and there are hundreds of mutations that are found within this gene. So it's highly impractical that we could take a blood spot, isolate the DNA and then begin searching through the gene for the many, many potential mutations that there are.
So we took a very practical approach, one that actually had been done mostly in European countries and that was to screen for a blood enzyme that is released when the muscle is damaged that's called creatine kinase or CK. If the CK is elevated, then we establish a threshold for what elevations we would consider relevant to finding the gene and then based on the threshold for the CK elevation we would then turn to looking at specific DNA mutations from that point forward.
Kevin Flanigan: So that CK enzyme is elevated in all or many kinds of muscular dystrophy, I guess.
Jerry Mendell: Correct.
Kevin Flanigan: Parents and patients will remember, at some point, they found it elevated as well.
Jerry Mendell: Correct.
Kevin Flanigan: Can it be elevated by other things at birth, I guess, is what viewers out there would like to find out?
Jerry Mendell: Absolutely. And that's one of the problems that many previous newborn screens had identified from muscular dystrophy is that as the baby comes to the birth canal there is enough muscle trauma so that the CK is elevated from the muscle damage and really the trick of course is to identify where in this CK elevation do we begin looking for mutations for the Duchenne muscular dystrophy gene.
That was one of our goals when we started this study and now at the conclusion of the study we have a clearer picture that we can talk about.
Kevin Flanigan: So you mentioned the CK had been used by some European, primarily, labs, maybe you could take a minute and give us a historical perspective of CK testing. What has it told us? Is it on-going elsewhere? Where did the field stand before this paper?
Jerry Mendell: Well, I'll start out by saying that what we did here was we took what we call a two-tier approach. We screened for CK and then did DNA testing and this is the first time this approach had been used for Duchenne muscular dystrophy. All previous studies and they go back to the late 1970s when just CK testing was done.
And the problem here is if you try to do just CK testing in the first 24 to 48 hours as I said you'll find many, many that are elevated from birth trauma and these are what we call then false positives for those patients or those babies who really don't turn out to have the disease.
So there has to be another level of testing that's put in place if you're going to do newborn screening in the first 24 to 48 hours that we do for all the newborn screens in the state of Ohio and throughout the U.S.
In European counties they approach this a little differently because they have a different healthcare system. In most European countries they have mandated healthcare systems that have all the children come back for six-week checkups.
Now there are advantages if we could potentially do that in the U.S. The advantages being that most of the CK that's elevated from going through the birth canal is already back down to normal levels and the CK could be done at the six-week time point. If it's elevated at that time then there are fewer false positives and then you can go on right on to DNA testing.
That is something that we cannot implement in this country. We can't mandate that all babies go back to see their doctor at six weeks or even at any time and we would miss many, many cases.
So we had to figure out a way that we could accomplish both tasks. We could establish the CK elevation and that CK elevation then would allow us to do DNA testing immediately and we would have the answer in a very short time and that's basically what we did and that's we call the two-tier system.
Kevin Flanigan: So it combined the genetic testing from that same blood spot. There's no second sample taken.
Jerry Mendell: That's a very important point, I'm glad you brought that up because what we don't want is added trauma to the baby and they have to have a blood spot. So from the blood spot that's taken at birth we can actually do the CK testing and we can go right on to their DNA testing for Duchenne muscular dystrophy and at the same time do all of the 35 mandated blood test or DNA test and biochemical test that are needed to fulfill the state requirements.
Kevin Flanigan: What spur this project on right now at the moment, so the technology is there clearly but are there issues related to treatment and possibilities now in particular that bring it forward or what inspired you?
Jerry Mendell: Well, I think the advances in muscular dystrophy are happening very rapidly. We have multiple treatment possibilities that are now on the table that were never there before. And obviously, the sooner we can implement those treatments the more we can help children with muscular dystrophy, the more we can prevent their muscles from breaking down as time goes on.
And the average diagnosis of muscular dystrophy still is not made until the earliest is usually three years old but more likely even five, six years old. By that time, there is tremendous amount of muscle loss and what we want to do is to start treatment as early as possible.
So that by doing newborn screening, identifying a baby with Duchenne muscular dystrophy within the first few weeks of life would potentially allow us to begin treatment. And there are multiple treatments now that are very rapidly evolving because the science for what we understand about how to manipulate the gene, how we replace the gene are all really being tested around the world and it looks very promising for these kids.
So by the same time we develop newborn screening, we hope to have clearly on the table a treatment that will allow us to start it at an early time.
Kevin Flanigan: It's true, I supposed also, that early treatment with steroids might be a potential benefit or something worth studying if we could identify these kids early enough.
Jerry Mendell: Well steroids are close to my heart in the sense that as a group of investigators we were able to establish that steroids were beneficial for Duchenne muscular dystrophy as far back as the late 80s. And it's unequivocal evidence that steroids helped kids with muscular dystrophy. Usually at the current time, we start treatment at five years old.
Some people are more aggressive that they would even start steroids, when we say steroids we're talking about glucocorticoids, at four, five years old. And we know that this helps the disease and there have been studies now that clearly showed that the earlier that you implement treatment with glucocorticoids the better the outcome.
And so this makes it even more possible without even going on to the new treatments that we could start treatment at an earlier time and help kids with this disease.
Kevin Flanigan: So in this paper you studied more than 30,000 dried blood spots and you mentioned that you were able to establish the normal range and cut out failures for CK. Tell us a little bit about mutation detection in these same samples.
Jerry Mendell: Well, when I've referred to DNA analysis, we are referring to specific mutations in the gene. And, as I mentioned, there are virtually hundreds of mutations in the gene but the science of detecting mutations has also advanced very rapidly and we were fortunate enough to work with one of your colleagues before you came here to Children's Hospital and that's Bob Weiss at University of Utah.
And Bob has very sophisticated molecular diagnostic lab there that allows fairly rapid analysis of the Duchenne muscular dystrophy gene, I would say complete analysis. In fact, we validated the whole testing process before we ever started by going to the clinic and doing mock up blood samples.
We took blood samples from about 15 children with muscular dystrophy who came in to the clinic, put them on a dried blood spot and send them out to the University of Utah laboratory as unknowns. And Bob Weiss was able to identify every single one of those mutations. They were dispersed all over the gene, they were the most representative of the types of mutations, deletions and duplications.
So before we started this study we were very confident that the technology for DNA analysis had advanced to the point where we could go to the newborns and also be confident there that we would identify the mutations.
Kevin Flanigan: And how many DMD mutations did you find?
Jerry Mendell: Well, as you commented before, we actually screened a total 30,749 newborns and out of this population we identified six DMD mutations, which gives us an incidence of one in 6,200 newborns. When we looked at the worldwide incidence taking all the studies that have ever been done going back to the late 70s, as I've mentioned, the probable incidence on a larger sample as we move forward with newborn screening will be somewhere around one in 4,000.
Kevin Flanigan: And in addition to Duchenne mutations, you turned up other surprises, I guess.
Jerry Mendell: Well, there's a concept that has been nagging at newborn screening in general and this is the concept of false positives. False positive means that you identify CK elevation but you never find a mutation that corresponds to that CK elevation.
And we had originally planned in this clinical trial recognizing that certainly would be likely to happen that the CK elevations that were not found to have Duchenne muscular dystrophy gene mutations would be referred back to our MDA clinic and then we would treat those kids or handle those kids for evaluation like we do any child who comes to the clinic with the CK elevation.
But during the course of this study, we realized that we could approach this in another way. The false positive test could be analyzed if they didn't have a DMD mutation, Bob Weiss in his laboratory could then search for other common muscular dystrophy gene mutations.
And this provided confidence that if we wanted to extend this study to find these other mutations, we would be able to find other gene mutations that cause muscular dystrophy that resulted in CK elevations just as high as the Duchenne muscular dystrophy patients in this newborn period.
And a proof of principle, we identified three mutations for limb-girdle muscular dystrophy for kids that did not have Duchenne muscular dystrophy gene elevations. So, we demonstrated that the whole process could be undertaken in a newborn, you could identify the gene mutations for Duchenne muscular dystrophy but if the resources were available, resources mostly being money and permission and agreement by the state authorities that other mutations could be looked for, then the study could be extended to these other muscular dystrophy genes.
And as the technology even advances that will become easier and easier as we move forward.
Kevin Flanigan: Well, having developed this and validated this and shown it works, it's a terrific body of work. What are the next steps in the project for your center?
Jerry Mendell: Well, I think that as you know our center's working very hard for finding potential treatment, you mentioned glucocorticoids are already on the table. We have identified that Exxon skipping has great potential for treatment for muscular dystrophy, we're moving toward gene therapy that also has potential.
So we're very interested in moving this forward and as a result of this work, the Muscular Dystrophy Association has put together a workshop with expertise on the muscular dystrophy side and on the newborn screening side to establish guidelines if how a newborn screening will be brought forward to the clinic.
And this workshop will be held in September of 2012 and we anticipate that upon conclusion of that workshop we will actually be able to take newborn screening back to the state officials and actually at a national level there's a committee called the Secretary Committee on Inheritable Diseases of Newborn and Children. And this is a major committee that makes national recommendations for newborn screenings.
So we'll take the guidelines from the workshop, carry them forward to this national committee. And if they agree that those guidelines are well in place and the treatment prospects look good enough, I think we actually will have a very good chance of bringing newborn screening to the delivery room and making a huge difference as we move forward with muscular dystrophy.
Kevin Flanigan: Well thanks very much for taking the time to discuss this exciting work.
Jerry Mendell: Thank you.
Kevin Flanigan: This podcast was brought to you by Nationwide Children's Hospital and the Nationwide Children's Wellstone Muscular Dystrophy Cooperative Research Center. You can find out more about the muscular dystrophy program and about ongoing clinical trials at Nationwide Children's at our website, nationwidechildrens.org/muscular-dystrophy-podcast. You'll also find a link to the published abstract of the study that we discussed today.
Thanks for joining us and we look forward to next month.