Unraveling The Mystery Of Mucopolysaccharidoses (MPS) Clue-By-Clue

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Introduction

Prof. Paul Harmatz: I note that there is a URL for accessing the talk later at your discretion. So beginning just with a brief overview, I warn you, I'm not a geneticist. I'm a gastroenterologist who happened to get lucky 20 years ago to have a clinical trial in MPS6 under our site. And since that time, I spend virtually 100% of my time with MPS clinical or research activities.

So if you ask really hard genetics questions, I'll field them on to one of the geneticists who will be speaking in the next three sessions.

So just keep in the back of your mind that we're really focused on the seven MPS today. They fit within the category of lysosomal storage disease, and there are around 50 lysosomal storage disease described. Most are autosomal recessive. This is important to keep in mind. Hunter or MPS II is exception, so the inheritance will be quite different for Hunter.

MPS as a progressive, heterogeneous disease

It's important to remember that as pediatricians that this disease is progressive. So I give you characteristics for a two- year- old. When you see the same child at 10, the picture will be quite different. Most of these diseases result in accumulation of storage material. The disease process or identity is really based on the type of storage material that's present.

And as with any genetic disease, now we understand that each gene is quite complex. You can have mutations in many different places on the gene, and this results in very high variability. So you can have a whole spectrum of disease. And most of our enzyme deficiencies and all of the seven MPS we'll talk about are soluble enzymes within the lysosome.

But there are other mechanisms, including membrane transport proteins, post- translational modification enzymes. These are other mechanisms that occur at a much lower number. So introducing you to our family of MPS diseases, I showed some pictures. Some of these are my patients. One was a pain. From the internet. But, as you can see, the this is, this is the spectrum they and underlying you can see all of these, except possibly the sanfilippo disease, are really skeletal dysplasias.

There the predominant features usually start with skeleton and this is probably the most important feature which only some of the MPS have is cognitive delay, cognitive development and progressive, progressive neurologic decline. That so those two features you'll see in the severe Hurler you can see a patient who has had cognitive decline. You can see in a sample of the book patient also I can tell you I have severe cognitive decline.

But the others- Hurler-Scheie down to very well Hurler-Scheie patients who was part of the first MPS I trials and later a great benefit from inter people and this is a recorded case in the literature. Joe Muenzer a very close friend with one of our friends with MPS II normal function and see the skeletal disease that are. And the patient with Morquio syndrome work you know IV A, is has severe mobility problems but does have a son and a very full- life and marital- I mean my first MPS running from from slowly progressing intermediate to a rapidly progressing patient to.

It's a very accomplished author and academic and inspirational speaker runs a clothing line for MPS patients, patients with difficult fine motor. So we have a wide range within the MPS. We have a wide range within each of the different forms of MPS. You've seen this slide, I'm sure, before it. It lists the. The fact we have seven forms of MPS.

MPS IX is extremely rare. I've never seen this and and I think it's not usually considered in most of the differential patients that you'll see, even though in the others you may see two or three. In your life, your career, this would be highly unusual to see a hyaluronidase deficiency. But so we have six, really that we're focused on the and we have in some categories more than one enzyme.

Recognising MPS: faces, skeleton and diagnostic clues

So we have total of 11 enzymes and you have common names that have now been generally replaced by the type and note that the storage material varies depending on the, the type of NPS. So really was one of the milestones to recognize that the urine detection of storage material like these diseases and later led to the enzyme descriptions for each disease.

But when we're looking at diagnostic work, if we see only heparan sulfate, it leads us towards sanfilippo. We see combinations of heparan and dermatan. You may have MPS I, II, VII. If we have only dermatan, we are thinking MPS VI. If we have keratin and primarily keratan, you're you're moving to the Morquio as your diagnosis. So just emphasizing this, this talk was to focus on sort of pearls or clues that lead you to diagnoses.

Then I'm sure Roberto may, Dr Giugliani may show these slides later, but there are a few clinical findings that sort of trigger in your office that this is, this patient seems out of the normal for your spectrum, your experience in the wide range of children that you take care of and with all their, their variability, you have to sort of recognize that a few things are a little bit more than expected.

And faces, clearly we have what described as a coarse faces. We may have sort of prominent eyebrows, low bridge on the nose thickening and the orbit. We see large liver and spleen shown in this with the abdominal distension. There are many other features in this but in particular looking for a large liver and spleen and joint stiffness, contractures, abnormal bone structures and so the skeleton.

So faces, abdominal exam, skeleton, I can add, not shown on this slide. Delayed development, cognitive delay always. People would sometimes go towards autism, they might go towards a hearing problem with delayed speech, but it's basically all channels into the developmental delay. Keep in mind under joint stiffness and we'll show a case for that probably the earliest most frequent pickup that I've seen in most cases is the presence of a gibbus or a sort of hump on the lower back and that should really send red flags that we should be thinking about.

And this is primarily a bone dysplasia. I'm showing a range of diseases such as multiplex, abnormal hand films are very helpful, the short bones in the hand, thick cortices, the wide diaphysis. Hip dysplasia is a very common finding. You have to think about the cervical spine and instability as an important feature and then mentioning the gibbus that I pointed out is such an important feature in this disease.

You can see the abnormal vertebrae with beaking and sort of posterior movement that leads to the gibbus deformity. Keep in mind we mentioned earlier this is a progressive disease. You can see two of my patients that I've seen over the past 20 years. You can see the young lady that I showed who is the accomplished, very accomplished now in her mid- 30s.

So this is delayed but doing very, very well with these are both patients with MPS VI with rapidly progressing disease and then a patient with slowly progressing disease. And you can see how much more difficult it would be to recognize this slowly progressing patient, the severity and amount of change. It's much smaller to see in the rapid.

And then within each disease we have the wide spectrum based on the types of mutations and probably the amount of enzyme or activity of the enzyme. We're not able to do sophisticated measures that separate it based on enzyme. We can get some ability to identify differences based on genotype but it's not, it's often new private mutations. Most of the diseases are autosomal recessive so we have a lot of compound heterozygotes, one with a gene that we know is severe, one with a gene that we are not sure we've ever seen before.

So very complicated but for diagnostic purposes keep in mind that we have this wide spectrum. So your diagnostic strategy, one probably your clinical suspicion, this child just is not developing the way you expected, language is not developing, faces looks a little bit more coarse and we'll go through some of the other tips that help you. And then probably you will either you'll begin a diagnostic workup to help speed up diagnosis or you'll refer to a geneticist and depending on the access or delay you may get various distances down the diagnostic tree.

For a geneticist it would be really important for the pediatrician to have the clinical suspicion. They may send the urinary screen then it moves to a more sophisticated enzymatic testing. It's difficult to say the whole blood has to go overnight to a testing laboratory. We now have dry blood spot testing and worldwide availability and much more stable samples.

We find that the samples come from one country to another and could be sent from a pediatrician. Clinical suspicion, over and over you're looking at the skeleton, you're looking at systemic features, the liver, spleen, cardiac, hearing, you know many many different features of the disease and then may or may not have developmental issues and so MPS II should all three are often present, MPS2 all three are often present, and MPS III we mostly see an S. or mostly skeleton, but looking for hypermobile joints, not the contractures that we see with the other MPS.

Laboratory diagnosis: GAGs, enzymes and molecular testing

For MPS II, one of the unique features is we don't see corneal clouding. So we see an older patient with a lot of corneal clouding. We're leaning more towards MPS , MPS VI, MPS VII, but we're excluding MPS II. So those are small tips to help you along. Urine GAG, it's been the classic screening test. The original assays were all dye binding.

Many of the major labs do this assay, and you can see different labs shown here on the slide by Tim Wood from Greenwood. We have a few advisory panels looking at diagnostic techniques, and you can see how well correlated it is. But keep in mind that it changes with age. You really have to look at the age standards to be sure that this patient is normal or abnormal in comparison to his age group.

And keep in mind that we have many false positives, false negatives with the dye binding. So we usually will combine, historically we would combine the total with a qualitative, which is an electrophoresis looking for the different species. So that began to help us with separating MPS II, IV, VI, III. The patterns are shown on the electrophoresis, and they're different, and they represent the different GAGs that are stored.

So qualitative only for diagnosis. This dye binding quantitative we used as a screening tool. We used it a lot to follow response to therapy. And then newer assays, which have greatly improved our urine screening and follow- up are now the quantitative LC- MAP tandem mass spectrometry assays. And we'll show you some data that shows how much it has improved our sensitivity.

But, again, it can be negative. And any time we have clinical suspicion but a negative urine, we have to move farther. And the next step moving farther would be to obtain enzyme testing for molecular, depending on which is more available. And both are helpful, and both have pitfalls as well. So enzyme testing, I mentioned, difficult to ship.

Leukocytes, they have to go ambient. They have to arrive within 24 hours. You can now use dry blood spot for this. And the enzyme is actually measured within the leukocyte. If it's absent, that's the positive. So this is showing a Morquio population, very low enzyme, and a normal population. You can see the clear separation. There are a few false positive enzyme results.

Multiple sulfatase deficiency is a different disease. It's a deficiency of the last step of activation of the enzyme, if it's a sulfatase enzyme. And so you always have to do a second enzyme that's a sulfatase to be sure you don't have multiple sulfatase. You have a similar problem if you test fibroblasts, mucolipidosis can be a confusing diagnosis.

So those are nuances that a good laboratory will help you with. Molecular testing also has problems. We move to the sequencing for a specific enzyme based on the enzyme assay. That is the classic way. Sometimes now we're backing into the diagnosis when we have exome or whole genome analysis. But classically we ask for a specific enzyme to be sequenced.

Often you'd have the problem that one enzyme, one mutation is identified and not the second one so that's one problem that you run into, you have to be careful that the two mutations are not on the same allele and the other allele is normal. The diagnosis is not present. So it is always good to have parents included and each parent who tested.

A case: diagnosing an attenuated MPS

We've spent about 15 minutes on background. I'll now give you a picture of two cases, two diseases that I followed closely. And the first case was, you'll see why I emphasize having a high index of suspicion and not stopping early before you arrive at a full diagnosis. This was a child who was born with an uncomplicated pregnancy by C- section.

He looks a little bit large at birth, which is often the case in babies with MPS disease. At one year of age, mom was noticing a gibbus in his lower back. He was referred to ortho and ortho obtained the x- ray that you see on the right. You can clearly see the gibbus and the abnormal shape of the vertebrae.

Yes, too many children that have gibbous that is not MPS, but it still should trigger you to think about, is this a genetic disease? And so the other clue that this patient had, and there are some of these areas that we think about. The patient had an inguinal hernia. We look for clues with frequent respiratory infection. We can see acid in his middle ear, and eustachian tubes do not function well, and we don't usually often have that history.

This patient did not have developmental delay. He did have two healthy older siblings, a brother and a sister. You have multiple older brothers who are all healthy. It sort of weighs you against an X- link. It's not a guarantee, and we have a history of consanguinity, which sort of shifts us towards the autosomal recessive. And this patient had the potential for being recognized in 18 months when these first X- rays were obtained, but was not referred to genetics until about four years of age.

So we had an early but a short time loss in between first recognition and diagnosis. So looking at showing you some pictures, Bob was very generous to provide, you can see at 18 months there are some other features. There are prominent ribs, a little bit coarse faces, some hand contractures that might have been recognized, and you can see the gibbus form would be shown here at 18 months.

And then by four years, I don't have a head- on, but you can see clearly the gibbus present, and then at 15 years, a very extremely bright, active child has had multiple surgeries, has had benefits of therapy for the last 10 to 11 years. So we would like to pick up patients quickly with these clues and move them to therapy.

So as I mentioned, this skeletal dysplasia is along with cognitive development are probably the two features that will stand out most prominently for you. And the skeletal dysplasia, if you're suspecting, for instance, you had your films with the gibbous, someone suspecting this MPS or some other skeletal dysplasia would often be helped by obtaining a hand film and a lateral skull.

So you see the classic J- shaped sella, you see a hand film with very short hand bones. and that would have pushed you or a pediatric radiologist again has to put this in their spectrum of normal and decide that these bones don't look normal. So this patient at four went through a very good genetic service. They quickly got the x- rays and defined the skeletal, the dysostosis multiplex and referred them to an MPS clinic and our laboratory first step was the urine GAG with a dye- binding assay.

This historically was before the tandem aspect was available. You can see a value of 89 with a normal of less than 16. So patient is six- fold above the upper limit of normal for age. So yeah that's that's a very large elevation which shifts the patient into the rapidly progressive category. I caution you to look very closely at units because most of the original therapy publications used microgram per milligram or milligram per gram and you would look at the 89 and say oh it's less than a hundred they should have a mild slowly progressing course but if you make the conversion by multiplying the 89 by 8 you come up on 715 micrograms.

So a very high level expected to have rapidly progressing disease. Lysosomal enzyme analysis showed a low ASB. Other sulfatase were not completed at the time but mutation analysis showed compound heterozygote, two mutations even though we had talked about consanguinity, the difference of different mutations. So the diagnosis in this patient was MPS VI rapidly progressive. Our second case that we'll mention is a gentleman that shown here in his teenage years once we had him referred to our MPS clinic.

A second case: the diagnostic detective work

He started his journey with a orthopedic consult when he was eight years old and at that time he had hip and back pain and it's interesting looking at the consult note that ligamentous laxity and a subluxing patella were noted which later once we came to a diagnosis it actually impressed us with their clinical description. So three years went by and they were referred to a skeletal dysplasia clinic.

Again continued to have back and hip pain for three years. They thought it was a skeletal dysplasia. A very good radiologist present who suggested MPS, requested additional films because he had only his hip films to look at and they obtained a urine GAG that was mildly elevated. So at 15 with a normal up to 10 people old it is mildly elevated.

Should have been pursued but was close to the normal range and probably didn't impress the physician. So follow- up at 13. Now same clinic, foot pain, good walking, hip pain. He's using a wheelchair now intermittently. Had the appearance with bushy eyebrows, full lips, had a mild gibbus at a waddling gait. We'll show you a picture. Normal height and mental status.

So no cognitive issue and plot for the norm. Absolutely normal height. So those tend to confuse people. When you see the attenuated end of the spectrum, they repeat urine gag, obtain additional x- rays and MRI of the hip and you can see the spine shows the abnormal vertebrae. The hips show subluxation and a hip dysplastic hip. So he was referred at that time to our MPS clinic.

We noted the same physical features for healthy SIBs. Normal height, weight and the laboratory we sent at that time included the dye binding urine GAG and this was even less impressive than the earlier one. You can see a 7. 57 out of, with an upper limit of normal of 6. 5. So you could easily disregard this and not move farther.

We had a faint keratan sulfate band on electrophoresis, so a little bit of a suggestion that there might be an abnormal GAG storage. But the MPS enzyme panel showed a low GALNS activity and you can see 1. 61. Normal was down to 76.. All other enzymes: now by this point we were running full panels with other sulfatase, so it looked very suggestive of Morquio.

Then we sent molecular confirmation. We've sort of developed the principle that we really want multiple tests with different samples to confirm diagnosis, to be sure that we don't initiate therapy that's not correct the disease we're looking at. So we saw no mutations and we ruled out deletion duplication. So now what? What do we do? We would like to treat the patient but we are having trouble confirming diagnosis.

Just give you a little bit of flavor for what the tandem aspect has given us. We collected multiple samples from this patient over a week's time before any therapy and you can see that the one is the upper limit of normal. It's been normalized to the upper limit of normal or dye binding and so the median was 1.

1 for a GAG analysis. So some of these fell into the normal range slightly up. But on other samples but if we look at the tandem aspect we have almost threefold elevation and very consistent high value. So you would not at least overlook or disregard a GAG that shows on urine, but and in specific. So next step was I, without being able to confirm the molecular character, I asked for a second full- blood leukocyte assay.

We confirmed on a second independent sample that we had no gal in this and we had a lot of. We had the elevated GAG, we had clinical and bone signs. So we felt we we had a diagnosis and therapy was initiated. So Morquio and MPS IVA was the diagnosis very important? Before you start therapy always consider, make sure your geneticist and sometimes, depending on the availability, the pediatrician may end up following different features.

But we try to get screening, we try to get good standard baselines to look at the effect of therapy. So you're seeing a walk test, you're seeing a slightly wobbling gait of favoring of this right hip, but and then in the clinical trials we did a stair climb. Also it was not as helpful as the walk test.

New tools and newborn screening

So this is a slowly progressing patient and I can finish the story by saying that working with green, with genetics, they're a wonderful lab, a logo, a sort of the extra mile to try to help with diagnosis. So they looked on a research level at the this patient and their family and and we're able to identify a splice site abnormality with a additional component in the protein that was being synthesized- this 1.

5. It's not seen in normals and a patient, so RNA sequencing was the technique they used to identify that he had a much elevated level of this 1. 5. It's not seen in controls and doing studying the rest of his family, they had intermediate levels but not high enough to show clinical symptoms. So just finishing last two slides, we've given you many tips to try to or clues to look for in your diagnostic skills and practice.

That where we recognize that probably the best way to identify these illnesses, especially with new therapies emerging, is with newborn screening and this is. There have been many studies now for and collected with differentM NPS. Diseases. But you can see that we have younger brother and older sister and they both started enzyme same time. Sister was three to four and brother was a few weeks old when he started and at the end of the study, when brother reached three years and we were able to compare the skeleton and different disease characteristics- that the younger brother, starting earlier, had much less disease and this has been consistent across multiple sib descriptions.

And in the US we have Health and Human Services has what's called a recommended uniform screening panel. For us it's very difficult now to get new diseases added. The panel will consider one or two a year. But we've moved steadily forward with the MPS. We had approval in 2016 for MPS I in California. Actually, this has two years to bring up testing.

They were active by 2018 and then we were really really, really excited that MPS II has been added in 2022, so we'll be able to screen, hopefully within a couple of years through newborn screening. So this is really the best way to get therapy in this patient set in the first weeks of life. So just wanted to finish thanking all of the patients, in particular families, that have participated in developing therapies and furthering our understanding of MPS, and my special thanks to John Hopwood, who's been one of the major godfathers and pioneers in this disease area.

Questions and answers

Thank you. I apologize again for not having pictures and images for me on the screen that I think you worked forward to that, so I'm happy to take a few questions. I'll look in my chat box see if I can give you my best answer. The first question asks: are you able to separate the different MPS diseases by x- rays?

And my feeling is that it's not a good way to separate. It really gives you a clue that yes, it's MPS. It may be that you get a look. The MPS for a Morquio looks a little bit different from the other MPS. You have more joint instability, more severe genu valgum, for instance, but it's it's not as clear.

I think you have to use your. You can't separate. We see gibbus in all of the MPS. The spine will look similar. I think you may see much less bone disease with MPS III and you could miss it there. You have to think more about cognitive status and hearing, combined with some somatic features, but not as traumatic as I, II, VI, VII, where the skeleton will be your main factor.

Remember that the very attenuated end of each spectrum may have very limited skeletal changes also, so so it's a. It's a total picture with a few clues to help move you along.

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