Irwin McLean's filaggrin readthrough drug could be revolutionary

Recently I predicted that nothing resembling a cure for eczema would appear for at least 25 years. I followed that up with a prediction that if a surprise cure were to emerge, it would be an anti-itch therapy.

At least one reader disagreed, and pointed me to a strategy now being developed at the University of Dundee in Scotland: drugs to stimulate or enable filaggrin expression in patients with one or two defective copies of the corresponding gene, FLG. At least one such drug is in the very earliest stages of drug development, toxicology studies in animals. If the drug succeeds in human clinical trials, we might see it in clinics in about 15 years. Potentially, such a drug could help some of the patients most severely affected by eczema.

The best review on filaggrin I’ve seen was co-written by three authors, two of whose names I am familiar with as among the biggest in the field of eczema research: Irwin McLean, who led the team that linked mutations in FLG to increased risk of developing ichthyosis vulgaris and eczema, and Donald Leung, principal investigator of the Atopic Dermatitis Research Network. (The first author is Alan Irvine, a colleague of McLean’s who works in Ireland.)

FLG is a giant, and unusual, gene, one of the last to be sequenced by the Human Genome Project. It encodes an enormous protein, profilaggrin, which contains from 10 to 12 repeats that are cleaved off into individual filaggrin units. Filaggrin itself has several important roles in the upper layers of the skin: it flattens skin cells into their characteristic final shape; it helps bind these cells together into a barrier; and it breaks down into the acidic “natural moisturizing factor.”

Many mutations have been found in FLG. Interestingly, if you take any particular ethnic group (say Japanese), there will be a characteristic profile of mutations for this group that is likely to be different than the profile for another group (say Scottish).

FLG (read from left to right; red hexagons are filaggrin units.) Common mutations in Asian and European populations. Look how early the nonsense mutation R501X appears. Figure 3A from Irvine, McLean, and Leung's NEJM review

All filaggrin variants are either “nonsense” or “frameshift” mutations in DNA that encodes protein (as opposed to so-called “junk DNA”). In a nonsense mutation, the correct DNA base has been replaced with a wrong one, and the upshot is that the protein-making machinery, known as the ribosome, runs into a code that it doesn’t recognize; it can’t add an amino acid to the growing protein, and it stops decoding profilaggrin at that point.

If the nonsense mutation occurs early enough, before the first filaggrin unit in FLG, no filaggrin gets made at all.

I believe that with a frameshift mutation (in which one or more DNA bases are missing or added) the protein is very likely to be terminated soon afterward. The end result is the same: little or no filaggrin.

In his 2006 Nature Genetics paper, McLean and his group identified two mutations, R501X (nonsense) and 2282del4 (frameshift), which have turned out to be the most common in Caucasian populations. Both R501X and 2282del4 occur early in the first filaggrin repeat. That means that if you have one such mutation, you will have one good copy of FLG and one bad copy; and if you have mutations on both your copies of FLG, you won’t have any filaggrin at all, and there is a high chance that you have eczema.

Soon after their 2006 discovery, McLean and first author Frances Smith applied for a US patent,  “Prevention/treatment of ichthyosis vulgaris, atopy and other disorders.” The patent, number 8,338,386, was granted only recently, on December 25, 2012. It makes many claims, all relating to the ability of five antibiotic drugs, or potentially tRNA molecules, to force the ribosome to read through nonsense mutations.

McLean and Smith’s patent is aimed at the nonsense mutation R501X (they say so in the patent), because it occurs so early in the gene. Such a drug would also work for nonsense mutations later in the sequence.

The drug or agent would not work on frameshift mutations such as 2282del4, as I understand it.

One cool thing about a readthrough drug would be that it would have its strongest effect on people who had nonsense mutations on both copies of FLG. A readthrough drug would theoretically make both copies functional. People with only one mutated copy of FLG would still benefit from having that number increased to two.

In the patent,“atopy” is mentioned in the title and the background information, but neither “atopy” nor “atopic dermatitis” appear in any of the 14 explicit claims. I don’t know whether this matters. I'm not an IP lawyer. It seems curious that the inventors left it out though.

Another curious fact is that only five specific drugs are mentioned: gentamicin, paromomycin, neomycin, tobramycin and negamycin. There is no discussion of the drug discovery process—any tweaking of molecules for greater effect or less toxicity—that I can see. I don’t know whether this matters either.

From what I can tell, McLean’s group has at least one of these compounds, which has most likely been altered from its original structure, in “toxicology” (which means testing in mice, rats, etc.) (see page 16). If you look at this handy graphic provided by the FDA, you will see that toxicology studies are step 2 of 12 in the drug discovery-to-market process. So it is extremely early days and you have to keep in mind that, as I keep saying, almost all drug candidates fail at some stage of clinical testing.

A relevant factor is also that currently there is no FDA-approved drug that acts by this mechanism—by causing the ribosome to ignore nonsense mutations. Ataluren, a drug to cure Duchenne muscular dystrophy and cystic fibrosis, is a readthrough drug in phase III clinical trials. The FDA is apparently especially careful when approving drugs that are “first-in-class,” or the first of their general type. So it is worth following Ataluren’s progress closely; its success could mean that we might see an eczema readthrough drug sooner.

Hat tip to Anonymous (you know who you are)

Filaggrin mutations cause distinct pattern of eczema in children

The giant protein filaggrin has several vital functions in skin. People with mutated copies of the filaggrin gene (FLG) are at risk of developing eczema that begins earlier and is more severe than usual. A new population study by Danish scientists (published in the journal PLoS ONE) now shows that children with FLG mutations develop a distinct variety of eczema, with emphasis on exposed areas such as the cheeks and the backs of the hands.

The research, led by Hans Bisgaard at the University of Copenhagen, could in the future help doctors diagnose children at risk of developing eczema and design personalized treatment for them—including therapy that could change the course of the disease.

The researchers analyzed data from the Copenhagen Study on Asthma in Childhood, which comprised 411 children born to mothers with asthma and followed them over the course of seven years, with checkups every six months (or more often, if eczema flares warranted). The scientists tested DNA from the children, checking to see if they had one of the two most common FLG mutations, known as R501X and 2282del4.

The results were not as cleancut as one might like. Roughly 15% of the 170 children who developed eczema had FLG mutations. But so did 7% of the 212 children who did not develop eczema. So clearly having mutated FLG does not guarantee eczema, and there are other factors at work to compensate for the mutation or cause disease to develop even if you have good filaggrin.

The researchers found that, in general, short- and long-term symptoms of eczema were worse in children with mutated FLG; and the disease set in earlier and flares tended to cluster in certain areas, most importantly  the cheeks and backs of the hands.

What is your child’s eczema like? Or what was yours like as a child? Does it fit this pattern? I seem to remember it concentrated on the backs of my knees and the insides of my elbows. But over the years it has moved around a lot. Maybe we will see scientists develop a catalog of eczema subtypes caused by known mutations.

Filaggrin mutation means more persistent eczema

The super-protein filaggrin helps skin cells take their proper shape as they develop into the upper, outer layer of skin; in its last step, it disintegrates into molecules that help the skin lock in moisture. Back in 2006 a landmark discovery showed that mutations in the filaggrin gene made it likely that the gene’s owner would develop eczema. But even though filaggrin is the poster child for eczema genetics, not that many eczema patients—only about 15%—have mutated copies of the gene.

Now researchers led by David Margolis, a professor of dermatology at the University of Pennsylvania, have shown that, among children with eczema, those who have filaggrin mutations are more likely to experience persistent eczema symptoms than those who do not.

The scientists analyzed data from the Pediatric Eczema Elective Registry (PEER), an ongoing 10-year registry maintained by Novartis to monitor the long-term safety of using pimecrolimus 1% cream. The new results are in press at the Journal of Allergy and Clinical Immunology.

The difference is subtle: at any time up to about four years of follow up (the period covered by the study), a child with a filaggrin mutation and a history of eczema is roughly 50% less likely to have clear skin than a child with two good copies of filaggrin. [Thanks to Margolis for helping me understand odds ratio.]

Interestingly, the authors noted that although all the mutations they studied were “null” mutations—that is, if you have one of these mutations, that copy of filaggrin doesn’t get produced at all—children with different mutations responded differently to treatment with topical steroids. Kids with the most common mutation, R501X, were most likely to need to use steroids to clear their skin. The authors don’t have an answer why this might be so.

Will we see gene therapy for eczema?

The European Commission is close to approving the first gene therapy in the Western world, according to the New York Times.

The treatment, called Glybera and developed by the Dutch company uniQure, treats a rare condition in which people are unable to break down fat-carrying molecules.

Gene therapy is one way that I imagine patients of the future might be cured of eczema. Glybera gives us a peek into how that might happen.

In gene therapy, doctors replace a patient’s faulty gene with a good one. The large protein filaggrin is currently the best candidate for eczema gene therapy. Several studies have linked filaggrin mutations to a higher risk of developing eczema.

Filaggrin gene therapy would have to be applied early in life. This is because in our current understanding, eczema is caused by a skin barrier defect that allows allergies to develop after a critical time window. Filaggrin mutations cause a faulty skin barrier. So you’d have to fix filaggrin early, because waiting too long would allow allergies to develop, after which fixing filaggrin solves only half the problem.

Glybera is a biotherapeutic, a gene (length of DNA) that is attached to a well-characterized and benign virus. Doctors will inject Glybera into leg muscles, where the virus infects cells and incorporates itself and the therapeutic gene into the patient's DNA—but only in leg muscle cells, presumably because Glybera gets absorbed locally. Then the patients will be able to break down the fat-carrying molecules, and their blood will no longer be overloaded with fat.

A biotherapeutic for eczema would likely be an intact filaggrin gene incorporated into a similar virus.

Gene therapy for the skin would have to be restricted to skin cells. You could accomplish this with a topical cream or ointment applied in the clinic. I'm guessing you would want to treat your whole skin, not just spots that were flaring up at the time.

How long will it last? The effects of Glybera apparently last for years, probably because muscle cells live a long time. Skin cells are a different matter—they are turning over continually. This could turn out to make gene therapy for skin conditions near-impossible.

But perhaps you could take regular doses—pills or injections—of a gene therapy that includes a genetic switch that turns on only in skin cells.

The critical early window for developing allergies in eczema patients could turn out to be a bonus in disguise. Maybe filaggrin gene therapy would only be required during a window of a few years, after which it could be discontinued and allergies would never develop.

Obviously extensive clinical trials for safety would be necessary. I could imagine this type of therapy becoming available within two decades. My grandchildren could be among the first to benefit.

Japanese scientists develop filaggrin-knockout mice

Something I've been meaning to cover is that Japanese scientists recently reported that they had developed a strain of lab mice in which the gene for filaggrin had been "knocked out."

That is, these mice, which are inbred for genetic purity, are missing the filaggrin gene. Their skin contains no filaggrin.

Filaggrin is a giant protein that consists of a chain of repeated components. It helps create the flattened structure of upper skin cells, and then breaks down into smaller, acidic molecules that form a natural moisturizing factor and probably help combat infection.

This will be a valuable experimental tool going forward. Paradoxically, a mouse model without filaggrin can teach you a lot about what filaggrin does--because it will be absent in those mice.

Using these new mice, researchers can focus on specific aspects of the skin, including various molecular pathways, and by comparing the knockout mice to regular mice, they can see what roles filaggrin plays.

Not surprisingly, the knockout mice have "dry, scaly skin" that lets more antigens through. Despite the skin's obvious fragility, the scientists find that the upper layers are normally hydrated, and show no increased tendency to lose water to the air.

The research was led by Masayuki Amagai at Keio University in Tokyo.

Jon Hanifin: Barrier defects come first in eczema; allergies follow

Atopic dermatitis is a disease that arises primarily because of a breakdown in the barrier properties of the skin, and allergic reactions typical of AD are a consequence of this breakdown, Jon Hanifin told an audience last week at the annual meeting of the American Academy of Dermatology, held in San Diego.

Hanifin is one of the US's leading dermatologists, and practices at Oregon Health and Science University in Portland. He was kind enough to send me the Powerpoint of his talk, which I wanted to read because I figured from its title ("AD Pathogenesis: What's New") that it would give me a good picture of the field.

His talk was encyclopedic and technical and I'm not going to attempt to cover the whole thing. But it did make clear to me that the standard model for how eczema arises and develops is in a state of flux.

For a long time, it was thought that allergy was the dominant factor in eczema. But a key paper in 2006 linked higher risk of developing eczema and asthma to mutations in the gene coding for the protein filaggrin. Filaggrin is a long protein, consisting of a string of subunits, that has an important structural role in skin cells, especially in the uppermost layer (the stratum corneum), and also gets broken down at the surface into something called "natural moisturizing factor." From that first paper came a flood of research into filaggrin, which has helped paint a fuller picture.

One thing that jumped out at me from Hanifin's talk was that the relationship between filaggrin mutation and eczema is not simple. The severity of eczema depends on where mutations are within the protein; it's possible to have more than one mutation, which greatly increases the likelihood that you'll get eczema.

Hanifin cautions that filaggrin is not the only genetic culprit in the origins of eczema. Mutations in certain other proteins can compromise the skin barrier.

If filaggrin is messed up, your skin barrier will be too--it'll be leaky--and this means that your body gets exposed early on to a wide variety of antigens that it otherwise wouldn't be. Recently I wrote about the "hygiene hypothesis," which posits that it's good for kids to get exposed to germs because that helps prevent allergies later on, but it seems that it's not good to get exposed to too many germs, because that leads to allergies later on. There's a Goldilocks-just-right amount of germs that your immune system needs to encounter to develop properly. Hanifin laid out the current thinking, which goes as follows:

• Defects in skin cell proteins let in irritants, microbes, allergens
• This causes skin cells to release a signaling molecule called "TSLP"
• TSLP stimulates white blood cells to develop an immune system dominated by type 2 helper T cells (which act via antibodies and inflammation, rather than by macrophages that eat pathogens)
• Th2 cells induce production of IgE antibodies, and then you have classic allergies linked to eczema.

It's just a logical progression. Allergy caused by skin defects seems generally to make more sense to clinicians and researchers these days than skin defects caused by allergy.

Now, is it possible to have atopic dermatitis without abnormal IgE/Th2? Hanifin replied by email:

Yes, roughly 20% of AD patients have typical eczema without any Th2/IgE abnormalities or asthma, etc. ( I call that "pure AD" but allergists tend to call it "intrinsic.") It's been known for years and is the reason we've always doubted that allergy was causative for the skin disease--IgE is clearly involved with hay fever, food allergy and some cases of asthma that usually accompany AD.

Hanifin lays a lot of stress on the precise definition of food allergy, which is specifically defined as an adverse health effect, rather than an adverse immune response. (He refers you, and me, to the NIAID Food Allergy Guidelines.) A positive IgE test for a food doesn't necessarily mean you're allergic. You have to get ill after eating something to be truly allergic to it. Hanifin clarifies:

Not necessarily ill, but usually rapid onset of hives, maybe nausea, cough--sometimes anaphylaxis...The tests are often imprecise and not everyone with high specific IgE levels reacts to that food. Whether they have become tolerant or never were allergic can only be speculated.

My guess is that Hanifin and other dermatologists are increasingly under siege from overinformed patients such as myself who have garnered information from the internet and are now demanding that their doctors conduct allergy tests to nail down the one or two things they're convinced must be causing their eczema. In his email, he comments that there are currently "enormous financial incentives associated with the belief of allergy causation of AD." Patients, and the insurance system, are paying a lot of money for test results that aren't useful.

What I'd like to see an explanation of is why most children grow out of eczema. What is it that's happening to their skin barrier and immune systems as they mature over the ages of 3-8 or so that is freeing them from the disease? Maybe, if we knew, we could capture and intensify that process and apply it to at-risk children and adults who have remained affected.

The plot thickens (as the skin gets thinner)

A paper published online today in the Journal of Allergy and Clinical Immunology changes our picture of skin barrier defects in eczema. A large research group (from eight institutions, including six in the U.S. and two in Germany) has shown that there is another upper skin layer protein besides filaggrin that, when mutated, is a likely cause of eczema.

The newly fingered culprit, claudin-1, is a component of "tight junctions," which bind neighboring cells together and form a seal against permeating allergens and pathogens. Tight junctions occur in the layers of the skin BELOW the stratum corneum. It is in the stratum corneum that filaggrin performs its job of flattening skin cells and getting digested into "natural moisturizing factor."

The paper is pretty comprehensive. The scientists found that

• the skin of patients with eczema contains much less claudin-1 than skin from "normal" people 
• afflicted skin is much more porous to ions than normal skin
• knocking out claudin-1 from skin cells increases the permeability of a layer of these cells
• in patient samples, the less claudin-1 that is present, the higher the levels of IgE antibodies
• and, in a population study, there are several point mutations of the claudin-1 gene that are statistically associated with eczema.

There are also several aspects of the research that are important to patients with eczema:

I saw in the funding acknowledgements that the lead author, Anna De Benedetto, and the senior author, Lisa Beck, both from the University of Rochester (NY), were funded to some extent by the National Eczema Association. Go NEA!

In the research, the authors made extensive use of samples from the Atopic Dermatitis Research Network, which is the precursor of the Atopic Dermatitis Vaccinia Network (a $32 million behemoth of a project that is 100x larger than the average NIH-funded eczema grant).

And I note that the University of Rochester has applied for a patent for the concept of using drugs to stimulate claudin-1 expression in the skin as a method for eczema treatment. It's funny; I've spent time as an engineer in industry and I work all the time with technology transfer and startup companies, but I was raised in a family with decided socialist tendencies, one of these being a knee-jerk anti-industry outlook. Or maybe that's just me. While I've learned to see that not all capitalism is evil--for instance, what would I do without Aveeno, or the companies that manufacture my steroid ointment? And don't I like my iPhone and the MacBook I'm typing this on?--my immediate reaction upon learning that a university has taken out a patent is to think "The greedy so-and-sos."

But that is misguided. And I quickly readjust; a patent is absolutely necessary to protect the intellectual property in a case like this. In the end, if a claudin-1 stimulant is an effective treatment for eczema, it will be a company that has to develop it and take it through clinical trials, which are horrendously expensive. (The rule of thumb is that it costs $1 billion to get a new drug approved by the FDA.) No pharmaceutical company or venture capitalist will invest in a drug lead for which the intellectual property isn't secure. It is good for you and me that the University of Rochester has immediately begun the patent process.

Moisturizer alcohol burn bad; acid moisturizer good

Voov had another dermatology appointment today. Nothing urgent; just a checkup to see how she's doing on her restricted diet. The new development is that we are not to apply steroids unless she's having a significant flare. Hidden B has, it turns out, been putting Derma-Smoothe on Voov every second night (Hidden B and I trade kid duties on alternate nights) and every morning. "I can't tell what's a significant flare," she says. "They all look significant to me."

I, on the other hand, don't think Voov's skin has been bad for quite some time. So, on my shifts, I haven't been putting any Derma-Smoothe on. This is what happens even in a two-doctorate family: we don't know exactly what we're supposed to be doing with our kid.

I mentioned that recently I got suckered into buying some generic moisturizing "creme" at CVS. It sits right next to the Eucerin, comes in the same kind of jar, and costs half as much. Why do I have to learn this lesson over and over again? The CVS creme sucks. It's slippery and actually burns my skin, although the ingredient list is virtually identical to Eucerin's. (Not perfectly identical, though, and I'd guess that the CVS version has more alcohol.)

Anyway, Hidden B found Eucerin on sale at Target and got me two jars. So I chucked out the CVS stuff. Burn begone.

This month's Journal of Allergy and Clinical Immunology has an article you'd find interesting. (Editor's summary here.) Let me recap it for you.

Two amino acids that naturally occur on normal human skin can slow the growth and reduce the infectious potential of the bacterial pathogen Staphylococcus aureus, a group of Irish scientists have shown in laboratory experiments.  

S. aureus colonizes the skin of 5% of people without eczema, and 90% of people with eczema; it infects broken skin and secretes molecules that cause and prolong inflammation.

Normal skin controls S. aureus with antimicrobial agents and an acidic pH (about pH 5.5, compared to normal cellular pH of about 7.4). I am not sure what acids are responsible for this low pH; however, two products of the breakdown of the molecule filaggrin (see here and here), "UCA" and "PCA," are amino acid components of "natural moisturizing factor" known to hydrate the skin and possibly contribute to its acidity.

The scientists explored whether UCA and PCA could, in a test tube, inhibit the growth of S. aureus. The answer was yes. UCA and PCA also reduced bacterial production of proteins necessary for S. aureus to colonize skin and evade the immune system. The interesting thing is that the scientists found the same inhibitory effects when they used hydrochloric acid instead of UCA and PCA. So the acidity of amino acids, rather than some other chemical property, is responsible for much of the bacteria-controlling effect.

However, there is one area in which UCA and PCA appear to have special properties: they greatly reduce bacterial production of one iron-sensing protein that helps S. aureus stick to skin cells. Hydrochloric acid does not do this.

If anything from this research might prove useful in the future to eczema patients, it would be that chemists might consider adding UCA and PCA to moisturizers to provide antibacterial control. There is evidence (referenced in the paper) that acidic moisturizers help suppress S. aureus.

Fantastic filaggrin article

I'm genuinely excited today. I found something much more interesting than the usual crop of eczema news. In the magazine The Scientist--which has a tradition of features that have a strong strain of narrative writing--that is, story, rather than just a gaggle of facts and jargon--I found an article written by Irwin McLean, a professor at the University of Dundee in Scotland. McLean is the lead author of the landmark papers that reported, first, mutations in the filaggrin gene that cause ichthyosis vulgaris, a dry, scaly skin disorder; and, second, that the same mutations caused (or greatly increased the risk of) eczema.

Please read McLean's article. It is effin' awesome. It's written by an expert and as riveting a read as you'll find anywhere, if you're interested in eczema science.

Here's McLean's explanation of why filaggrin matters:

Filaggrin is crucial for the formation of the stratum corneum, the layer of dead cells at the surface of the skin, and also for the hydration of this crucial barrier layer. People who have mutations in one or both copies of the filaggrin gene produce dry and flaky skin that is permeable to allergens or chemical irritants. When the barrier is broken, foreign material is able to pass through these skin layers. We think that childhood eczema—which usually first occurs within the first few months of life—is an indication that foreign pathogens and irritants have passed through an abnormally porous skin layer, activating a strong allergic immune response, and thus priming the body to react to antigens that it would not normally encounter by this route. Later in life, when the child’s immune system comes into contact with those same allergens, perhaps through the lungs, it reacts aggressively, causing the inflammation in the lungs that results in shortness of breath. In fact, many children with eczema have multiple allergies to house dust, pet hair, and other substances.

McLean tells the story of how he and his team identified the mutations in the filaggrin gene (FLG). FLG is a remarkably difficult gene to sequence and was one of the last to be conquered by the Human Genome Project. It's very large, and contains 10 (or, sometimes, more) identical subunits, which means that if you start sequencing somewhere in the middle, as is done in a shotgun approach (where you sequence a lot of small bits and join them up like a jigsaw) you can't be sure if you're sequencing just one of the subunits, or more than one, or all of them at the same time. "It was as if nature was having a joke at our expense," McLean writes.

The team managed to identify the two mutations in ichthyosis vulgaris-- but then one of the scientists, Alan Irvine, pointed out that many of the patients in the subject group also suffered from eczema, many more of them than were in the control patient group. (It's this kind of insight that drives scientific discovery.) McLean, Irvine, and colleagues ran a statistical analysis on their patient group, which was very small by epidemiological standards--only 50 affected patients, and 200 controls, instead of thousands--and found that the  measure of significance, the "p-value," indicated beyond a doubt that there was a link between eczema and the mutations.

At the end of the article, here's McLean on what's next.

The question now is how to prevent eczema, asthma, and allergies from occurring in patients with the susceptibility mutations in their filaggrin gene. If it were possible to find a cure for eczema in adults, could we also cure asthma, or would it be too late, with the immune system permanently primed against allergens? I would argue that it might at least help. If the skin barrier is not repaired, then the immune system will constantly produce more antibodies in response to allergens that continue to get past the barrier. Stopping that assault may have some beneficial effects. The alternate possibility is that we may need to prevent eczema in young children before they become sensitized. If the latter proves true, would it be sufficient to curb eczema early in life, as the immune system develops? These are all questions we are gearing up to answer...

...We’ve also started to look for ways to help the body replace filaggrin at the cellular level. We are currently searching small-molecule chemical libraries for new classes of compounds that might induce skin cells to produce more filaggrin protein. Results look promising, and we are hopeful that in a few years’ time, new drugs or creams that enhance skin-barrier function will be available to treat these common diseases.

From McLean's biography we learn that he briefly worked at a biotech company, which is good news for us: he probably has some idea of how cures get from the benchtop to market.

I'm going to argue that HERE is where we need to put our money from philanthropic donors. Now that McLean and his team of leading scientists have found these mutations and laid bare the role of filaggrin in eczema, we need to help entrepreneurial scientists translate this research into startup companies or intellectual property that can be licensed to big pharma or biotech companies such as Genentech. THIS, the proof-of-concept stage, is where funding in the area of $100k can make a difference to an academic lab-- the difference between the science turning into real cures, or languishing in the pages of the scientific literature.

Filaggrin, I love ya

I wasn't going to post today-- a bit worn out after taking the kids to a Hallowe'en party and trying to keep Voov (wearing cute flower costume, for the second year) from eating soup and noodles, which are off-limits due to her food restrictions, while trying to keep Shmoop (wearing cute lion costume, for the third year) out of the desserts. Successful with the soup & noodles. Less successful with the dessert. And so, while Voov sits placidly in the bath, Shmoop has a giant screaming and kicking fit as he comes off his sugar high, and must be manhandled to bed.

But I just can't stop wanting to learn more about filaggrin. It's my protein of the month. Here's something else I found today: a 2009 review of the role of filaggrin in atopic dermatitis. (Several studies have positively linked two mutations in the filaggrin gene to a significantly higher risk of eczema.)

So: as I wrote last Saturday, filaggrin is this protein that skin cells start to produce as they move along the treadmill from the inner zones of the skin to the stratum corneum. When the skin cells get to the stratum corneum, filaggrin gets chopped up into short bits called peptides, and these peptides grab hold of the inner keratin skeleton of the cell and pull it all together, flattening the cells. A loss-of-function mutation in filaggrin means that your skin's outer layer is defective and, from the very first, it lets in many more pathogens and allergens than "normal" skin-- which may overstimulate the immune system and cause you to develop chronic allergies.

And now, in the 2009 review (which is a year old, so more has been learned since then) I find that filaggrin is no one-trick pony. It's more than a keratin scrunchie. Within the stratum corneum, the filaggrin peptides get progressively degraded and altered unto a mix of amino acids that, along with some ions, is called the "natural moisturizing factor." The natural moisturizing factor is, basically, your own Eucerin, and prevents water loss; it's also slightly acidic.

So when you have mutated filaggrin, not only does it mess up the structure of your skin cells, but it doesn't get processed into moisturizer, and your skin pH is too alkaline-- which has been reported to affect the composition of your T cell populations in the skin, and lead to inflammation.

Cool!

In the last paragraph of these papers, the authors always say something like "this work could lead to targeted intervention and therapy." (They have to, to justify more funding.) At some point, we, the funders, must ask: where's the beef? Tell us how this research is going to lead to therapy. New drugs? How exactly will they be discovered? New emollient strategies? Who's formulating them? And is there going to be any relief for adults who are already well along the atopic march?

A genetic origin of the demon itch

One problem with writing a blog is that you write each post separately. It's hard to keep a grand plan in mind and so, even if you think you're focused enough (e.g. eczema research and what it's like to live day-to-day with the condition) you keep getting buffeted around by the news of the day. Such as that PLoS ONE report I wrote about on Thursday.

Hidden B tells me I ought to follow up on some of the promises I made earlier on-- such as to look more deeply at filaggrin and heritability-- and that this would make for a less disjointed read. What Hidden B wants, Hidden B gets.

Two journals in particular have begun to emerge for me as great sources of information about genetics, allergy, and eczema research. There's the Journal of Allergy and Clinical Immunology, of which Donald Leung is the editor. Leung is the scientist leading the Atopic Dermatitis Research Network, funded by $32M from the NIH. So it's no surprise that his journal publishes some good, relevant research. I've read a few papers from the journal and have been impressed by the quality of the work and the writing-- and, believe me, you can't say this about every journal.

Look up "filaggrin" in Wikipedia. The first reference for the entry is a paper from J Allergy Clin Immunol. It's a great introduction to filaggrin and how it may be at the root of a large number of family-related eczema cases. This paper (Weidinger et al.) references a number of papers from Nature Genetics; the most important ones are from 2006, when, it appears, two overlapping groups reported finding loss-of-function mutations in the filaggrin gene that are associated with eczema. Filaggrin looks guilty to me. (See fascinating blog entry in the Nature system.)

But, as anyone with eczema knows, it's a complex condition; the underlying science appears just as complex. Weidinger et al. analyzed 476 German families: from each family, the parents and one child with AD. I haven't digested the paper fully; but of the 476 kids, roughly one-quarter had one of the two known loss-of-function filaggrin mutations. So there are evidently other molecular causes of eczema. Maybe there are yet-unmapped filaggrin mutations. Maybe there are mutations of other genes that screw up the same processes as mutated filaggrin. There are probably many, many paths to the same end.

What is filaggrin? It's a protein product of the FLG gene on the q-arm of chromosome 1. The gene itself is complicated, which is why scientists took a long time to sequence it. I look forward to learning more!

FLG is expressed as profilaggrin, a larger protein, in skin cells in the lower levels of the epidermis. As the skin cells move toward the stratum corneum, they start expressing different proteins and making lipids and other molecules to form barrier impermeable to pathogens such as viruses and bacteria. When skin cells reach their final state, before they slough off as skin flakes, the profilaggrin is chopped up into small bits called peptides, and these filaggrin peptides bind filaments of keratin inside the cells. The filaments then get cross-linked by enzymes--something like the way fiberglass and resin combine to make one godawfully tough material.

If you have a mutation in your filaggrin gene (these mutations appear to be dominant, from what I can tell) then your skin has a crappy fiberglass coating instead of a smooth, impermeable one. It lets water out; it lets pathogens and allergens in.

This skin defect may be at the root of eczema. As a baby, if your skin is defective, it lets in viruses and allergens, which induce inflammation. And then because of the chronic inflammation, you then develop the allergies and sensitivities that later manifest as the confusing food-, aero-allergen, and stress-related flareups of classic eczema.

So why does eczema affect 20% of children, and then mostly disappear--though not for me, nor 2% of adults? What happens as kids grow up?

Fascinating stuff! You can't blame the scientists for being interested. I just wish the problem was purely academic.

Eczema, a family affair

Did I mention that eczema runs in my family? Those that I know for sure have it, or had it, are my father's father (deceased), whose scratching and ill temper were legendary; a cousin; my sister; me; and my daughter Voov.

My grandfather was a sea cook and a veteran of World War I. His life was hard and eczema didn't make it any easier. Then eczema skipped a generation, fortunately for my parents, and in the interim science and medicine made great improvements in emollients and steroids. We've had it much better than he did. But let's not have the impression the problem is solved. I believe some day we'll have complete control over the demon itch.

Our family probably shares a filaggrin mutation. Ten years from now, when you can get your genome sequenced for a hundred dollars, I bet that's what we're going to find. In future posts I'm going to explore what filaggrin does, or in our case doesn't do, for skin. And I'm going to ask the scientists studying filaggrin how they think their discoveries might lead to therapies or cures.

This blog is soon going to become, like eczema, a family affair. I've invited my sister to contribute posts. She's a resident or whatever you call someone who is undergoing the legalized hazing that the medical establishment enjoys inflicting after you graduate with an MD. She'll add medical legitimacy. She gets to pick her own moniker--hopefully not something to do with ferrets (she doesn't have kids at the moment, just pet ferrets). Until then, I'll call her Dr. Sis.

Dr. Sis lives in Newfoundland. So this blog is a California-Newfoundland axis. We can speak with authority on both endless summer and endless winter. The mind boggles to realize that the two regions share a continent and a language--though the latter is debatable, if you've ever met a real Newfie.