This orphan has many parents

The Orphan Drug Act of 1983 was a game-changer for rare diseases.  A result of lobbying by patient-led groups such as NORD with bipartisan political support, its principal author was the liberal Democratic Congressman Henry Waxman and its signer was President Reagan.  The rate of FDA approval of drugs for orphan diseases increased from fewer than one per year before 1983 to an average of 13 per year over the ensuing decades.  The ODA provided drug companies 7 years of new patent protection, financial subsidies in the form of grants, a fast-track approval process and last but not least, a tax credit for 50% of the development costs.

A disorder qualifies for “orphan” designation under the ODA if its point prevalence in the US is fewer than 200,000.  PSP easily meets that criterion, with about 5,000 diagnosed cases or 20,000 if you count those who undiagnosed but potentially diagnosable.

PSP’s transition from an orphan to an object of loving care has been remarkable.  There are several reasons:

First, a drug that works for PSP may also work for other tauopathies, including Alzheimer’s disease.  Of course, a huge potential market exists in the ascendancy of AD as a major epidemiologic challenge for the Boomer Generation and beyond.

Second, the disappointing results of clinical trials of drugs addressing the beta-amyloid aggregation of AD turned the world’s attention to tau aggregation as the key to AD prevention.

Third, PSP, as a “pure tauopathy” offers a good, clean “test bed” for anti-tau agents.  (We now know it’s not so pure, but it’s close enough for present purposes.)

Fourth, neuroprotective trials are easier in PSP than in AD despite the recruitment difficulty arising from the disease’s rarity.  One reason is that PSP, unfortunately, progresses more quickly than AD.  (Aside: A “neuroprotective” trial attempts to reduce the rate of worsening of the disease, usually without improving the existing symptoms.  A “symptomatic” trial attempts to ameliorate existing symptoms without regard to the long-term progression or outcome.)  Demonstrating that a drug slows a disease’s progression requires fewer patients and a shorter treatment period when the untreated disease progresses more rapidly.  This translates into cheaper development costs and less development time.

Fifth, in the absence of a proven biomarker for AD, clinical trials must rely on neurological exams and reports of daily activities by patients and caregivers.  No such clinical scale accomplishes this adequately for AD, but the PSP Rating Scale does so for PSP.  (Bragging point disguised as a disclaimer: I developed the PSPRS.)

But the House of Representatives’ version of the new tax reform bill eliminated the tax credit in the Orphan Drug Act.  The thinking was that drug companies often charge prices for those drugs far in excess of their development costs, thereby defeating the original intent of the ODA to support development of drugs without a reasonable expectation of profitability.  The drug companies can usually get away with those prices because the patients are desperate and because the insurance companies providing prescription coverage want to avoid lawsuits and public-relations disasters.  Besides, the insurors can just raise their premiums to spread the cost over their other subscribers.

The other concern in the House was that drugs developed under ODA protection may then find use against more common conditions with highly profitable results.  Some examples are Cialis, Botox and Provigil.  A PSP drug subsequently used for AD could become another example, as pointed out above.

The final tax reform law is a compromise.  It reduces the fraction of the development costs that can be taken as a tax credit from 50% to 25%, not to zero.  How will this affect the drug companies’ calculations regarding future orphan drug development?  I haven’t a clue.  But my attitude toward this complicated situation is that patients with PSP should be glad that their disease is of interest to drug companies, even if that’s only a by-product of their interest in AD or some other way to game the ODA.

Some think tank now needs to figure out just how much credit the ODA deserves for recent decades’ abundance of new drugs for orphan diseases.  Maybe it’s not an economic issue at all.  Maybe it’s just that recent basic scientific breakthroughs have created more drug targets.  Or maybe the drug companies have figured out that they can charge tens or hundreds of thousands of dollars per year for a drug and get away with it.  Either way, maybe the ODA is unnecessary or needs to be radically revised.  One can hope that if the current work on PSP results in a mega-expensive AD drug that strains our present health care model, maybe the result will be a truly universal health care system in the US.


PSP by the Bay

Just returned from the annual CurePSP International Research Symposium, held this year in on the campus of University of California San Francisco on October 27.  About 120 researchers attended, many from Europe and Japan.  The first keynote speaker was Bruce Miller from UCSF, perhaps the country’s leading behavioral neurologist, who gave an overview of PSP/CBD research with an emphasis on activity of the Tau Consortium, the multi-institutional research group that he directs.  The other keynoter was Robert Stern, a neuroscientist at Boston University who directs clinical research at BU’s Chronic Traumatic Encephalopathy Center.

Bruce’s talk touched on many topics — from the nosology and pathology of the various cognitive/behavioral syndromes in the tauopathies to the sleep disturbance in PSP (hyperarousal is common in PSP, while hypoarousal predominates in CBD).  Perhaps most interesting was his up-to-the minute summary of the state of tau PET imaging in PSP diagnosis (not nearly ready for prime time, though potential exists).

Bob’s lecture summarized the story of CTE.  He emphasized that the most important frequent cause isn’t concussions, but the continual sub-concussive blows to the head such as those suffered by football players during routine blocking and tackling.  He was too smart to speculate much about a relationship between the tauopathy of CTE and that of PSP, but I’m not:  I’ll say that in both cases, individuals with a genetic predisposition to tau aggregation are exposed to a precipitating factor – repeated brain tissue stretching for one, some sort of toxin for the other.  If we can find the genetic background for one, we may find it for the other.

Perhaps the genetic answers will emerge from the whole-exome sequencing project that is complete and in the writing phase or the whole-genome sequencing project that is well under way. But as pointed out in another Symposium talk by Jerry Schellenberg, the U Penn geneticist who heads those efforts for the PSP Genetics Consortium, there’s a lot of “genetic dark matter” in the form of genomic deletions, undetectable by mere sequencing.

Maybe in future posts I’ll get more into the other excellent CurePSP Symposium talks – and the 18 concomitant poster presentations.  Or maybe I’ll get distracted by a random shiny object I find in somewhere else.

You’ve dragged me back, or: an anti-tau antibody update

Yeah, yeah.  I know it’s been 15 months since my last post.  I’m fine, thanks – just busy with other things.  But today a kind reader from Canada named Maureen posted a comment asking where I was all this time and threw in a little flattery just to get me going.  I’m a sucker for that.

So here’s the latest on the hottest topic in PSP-ology, the antibody trials.  Right now, five drug companies have anti-tau antibodies in the pipeline.  Two have started human trials and are in Phase 2.  The others are still in laboratory phases or in the early planning for human trials.  As a reminder, these antibodies are directed at the tau protein and are given by intravenous infusion, typically at intervals of a month.  The idea is to intercept the misfolded, abnormally aggregated tau as it passes through the intercellular fluid between brain cells. (We still don’t know if it’s between neurons or glia or both.)  The hope is to slow the spread of the disease process through the brain.  This treatment would probably not improve any existing deficits, just slow the rate at which they worsen going forward.

The first drug company out of the blocks was Bristol-Myers Squibb, which sold its neurodegeneration division to Biogen in April 2017.  This Phase 1 trial was designed only to assess safety and comprised only 48 patients, a quarter of whom received placebo.  The antibody passed with flying colors, with no important side effects over the 12 months of treatment.  The patients (including the 12 assigned to placebo for the first year) are continuing to receive active drug and are generating more data along the way.  The protocol did include measures of efficacy, the principal one being the ability of the treatment to slow the progression of the disease relative to placebo as measured by the PSP Rating Scale.  But that effect would have to have been huge to be statistically noticeable in so small a study.

That’s the purpose of the Phase 2 studies, of which 2 are in progress.  The one that Biogen bought from Bristol-Myers Squibb will include 396 patients, a third of whom will receive placebo infusions.  The study will take place at about 35 sites in the US, Europe and Japan.  Recruitment has begun and the double-blind phase will last a year for each patient, though it will probably take about 6 months to get all of the patients entered.  This study has been dubbed the “PASSPORT” study.  (It looks like an acronym, but it doesn’t really abbreviate anything, except that the letters “PSP” are in there somewhere.)

The one by AbbVie, another big drug company, comprises 180 patients, of whom 60 will get placebo.  It will take place at 18 sites around the US plus 3 in Canada, 2 in France and one in Australia.   About half of the sites are presently recruiting patients.  This study is called “ARISE.”  When I find out what that’s supposed to abbreviate, I’ll let you know.

You can find more info about both trials, including contact information for prospective participants, at  Here’s the listing for the BMS/Biogen study and here’s the link for the AbbVie study.

Maybe a future post will regale you with my random thoughts about whether anti-tau antibodies are actually likely to help.

[Full disclosure: I consult on an hourly basis for both BMS/Biogen and AbbVie in matters regarding the PSP Rating Scale, which I published in 2007 and is the principal outcome measure for both studies.  I have no personal financial interest in the studies’ outcome.]

Express yourself, or better yet, don’t.

An original and interesting observation just appeared that might help explain how the known genetic variants associated with PSP might cause the disease.  It has to do with regulating gene expression.

Mariet Allen, PhD, a junior researcher at Mayo Clinic Jacksonville, and colleagues published the paper in the current issue of Acta Neuropathologica.  The senior author is Nilüfer Ertekin-Taner, PhD, who received a grant from CurePSP for this work.  The general idea of using such “endophenotypes” to assess the role of genetic variants in causing PSP has long been proposed by their mentor, Dennis Dickson, MD, a leading neuropathologist, who was also an author of this paper.

They used tissue from 422 brains from the CurePSP Brain Bank at Mayo that had been confirmed as having PSP.  They made three types of measurements in each brain: gene expression (measured as messenger RNA), epigenetic methylation of DNA (measured as CpG islands), and numbers of the various classic PSP micro-anatomic changes that have been known for decades.  They correlated those measurements with whether each case carried the major or minor allele of markers reported in  the genome-wide analysis (GWAS) of single-nucleotide polymorphisms published in 2011 by Hoglinger et al. (Disclaimer: I was a minor co-author on the 2011 paper.)

Without getting too much into the details, the results were that the genetic variants and increased DNA methylation at MAPT (the gene for tau protein) and/or MOBP (the gene for myelin-associated basic protein) were associated with increased expression levels of some proteins not previously associated with PSP.  One such protein was “leucine-rich repeat-containing protein 37A4” or LRRC37A, which is coded at chromosome 17q21.31-q21.32.  The genetic marker status at that location was also associated with increased expression levels and methylation levels in two other proteins encoded by genes at the same approximate location, ARL17A and ARL17B.  (Adenosine diphosphate ribosylation factor-like GTPases are involved in protein transcription and like LRRC37A, are located next to the MAPT gene on chromosome 17.)

LRRC37A appears to be involved in regulating interactions of proteins with other compounds.  Its upregulation is known to be harmful to cells.  Intriguingly, its gene produces a wide variety of alternatively spliced protein forms (where some exons’ protein products are included, others excluded, from the finished protein product) in different people and in different species.  This may suggest that this gene is unstable and could easily be induced to make an inappropriate variant of its protein by a subtle exposure to a toxin or a toxic effect of another gene.

Furthermore, the marker status at the MAPT locus correlated with more intense tau aggregates in the form of coiled bodies and tufted astrocytes, two of the standard diagnostic features of PSP.  This reinforces the idea that tau overexpression is part of the pathogenesis of PSP and that inhibiting that expression could provide prevention.

So as the authors modestly conclude, “MOBP, LRRC37A4, ARL17A and ARL17B warrant further assessment as candidate PSP risk genes.”  All of these associations may suggest new drug targets, but it’s a long slog from there to the clinic.  However, if someone screens a library of existing drugs for their ability to suppress overexpression of these proteins, the path to a treatment could be much, much shorter

Critique of pure prionopathy

If you follow the latest in neurodegenerative disease research, you’ve heard the “prion hypothesis” or “pathogenic spread hypothesis.”  For the past five or six years, it’s been widely claimed, and almost as widely accepted, that the proteins that mis-fold and aggregate in the brain cells in PSP, as well as in its big brothers Alzheimer’s and Parkinson’s and the rest, spread through the brain in a way similar to how prion protein spreads through the brain in the prion diseases such as Creutzfeldt-Jakob disease, mad cow disease and kuru.  A respectable body of experimental evidence supports — or at least is compatible with —  this idea.

But now a pair of highly respected Harvard neuroscientists, Dominic Walsh and Dennis Selkoe, have said not so fast.  In a very well-balanced and dispassionate review of the prion hypothesis in Nature Reviews / Neuroscience, they show that while the existing evidence is compatible with cell-to-cell spread of toxic protein aggregates, there is still plenty of room for a hypothesis that posits selective cell vulnerability with a more generalized toxic influence.  I won’t get into the technical weeds, but here are their major points:

  1. Even in the classical prion disorders, it is well-accepted that “cell-autonomous” factors, rather than just spread from nearby cells, determines which cells are and are not involved.  The salient example is that the asparagine-for-aspartate mutation at position 178 in the prion protein causes familial CJD when the person has a valine at position 129 in the same protein but causes fatal familial insomnia with there’s a methionine at 129.  (Neither of the latter substitutions by itself is pathogenic.)
  2. The “pathogenic spread” hypothesis rests in no small part on the observations of Braak and colleagues that early-stage Alzheimer’s or Parkinson’s pathology in people dying from other causes is confined to certain specific brain areas, suggesting that the process starts there and spreads.   But Walsh and Selkoe point out that those early sites of pathology may merely be the areas most sensitive to a generalized insult.  Furthermore, only about half of the cases of each of those diseases followed that pattern.
  3. Another buttress for the pathogenic spread hypothesis is the observation that 5-10% of fetal substantia nigra cells transplanted into the striatum of patients with Parkinson’s developed Lewy bodies themselves after a number of years. But this need not be the result of spread of pathogenic alpha-synuclein; it could be the result of a more generic insult such as inflammation in the injection site, where most of the injected cells have died.  They cite evidence that activation of microglia (the brain’s inflammatory cells) in other types of neural grafts can produce Lewy bodies in those grafts.
  4. The experiments showing that injected alpha-synuclein or tau protein can induce the formation of aggregates in host brain is incomplete because they do not adequately demonstrate actual cell loss or impairment of brain function in the host animal. We know from other lines of experiment that aggregates alone do not correlate well with neurological impairment in human or experimental neurodegenerative disease.
  5. The pathologic anatomy of rare, dominantly inherited forms of Alzheimer’s, Parkinson’s and frontotemporal dementia fits well within the spectrum of their corresponding sporadic conditions. A genetic cause, producing the same intense pressure for protein aggregation in many areas of the brain simultaneously, would not be expected to mimic the anatomic pattern of a single-anatomic-source process posited by the pathogenic spread hypothesis.
  6. There are still many questions left unanswered by the pathogenic spread hypothesis. This doesn’t directly contradict its other tenets, but it weakens its explanatory power. It cannot explain the initial protein misfolding; how the aggregates are released; how they remain aggregated in the interstitial fluid where the concentration of the protein is far less; why they don’t stick to the outsides of cells after being excreted, as their physical chemical characteristics suggest they should; how they choose only certain target cells to penetrate; and how the aggregates escape into the cytoplasm from the membrane vesicles that presumably would be the vehicles by which they penetrate their targets.


As a final point, Walsh and Selkoe make a case for avoiding the term “prion-like” or “prion-oid” with reference to neurodegenerative diseases unrelated to the prion protein itself.  They list several known features of prion protein spread in the known prion diseases that as far as we know are absent in PSP, Alzheimer’s, Parkinson’s, etc.  They also cite the absence of any known transmissibility of the non-prion-protein and point out that we don’t know enough about either group of diseases to equate them at that level of terminology.

Excellent scientists that they are, Walsh and Selkoe describe a set of experiments to undertake and new research tools to develop in order to strengthen or reject the pathogenic spread hypothesis.  Maybe I’ll get to that in another post.  But they end with the hope that the pathogenic spread hypothesis is true, for that would provide many potential therapeutic targets that would not otherwise exist.

A new definition of PSP

When you design a research project in PSP, it’s important to make sure that everyone in the subject group with PSP in fact has PSP. Otherwise, you degrade the statistical power of the trial to detect any benefit of the treatment. The standard diagnostic criteria for PSP (called the “NINDS-SPSP Criteria” and spearheaded by Irene Litvan, MD, now of UCSD) were published in 1996 and have worked well for that purpose; Their positive predictive value (the fraction of patients satisfying the criteria who actually have PSP) and specificity (the fraction of those without PSP who fail to satisfy the criteria) are close to 100%.
But as we now enter the new era of trials of experimental neuroprotective treatment for PSP, we would like to diagnose the disease at an earlier stage, when such interventions are most likely to be effective, and the NINDS-SPSP Criteria don’t do that so well, with a sensitivity of about 80% overall, certainly lower in early cases. Another shortcoming is that the various phenotypes of PSP that have been described since 2005 won’t in many cases satisfy the criteria, which were designed for the “original flavor,” now called PSP-Richardson’s syndrome.
So time has marched on and we need a new set of criteria. Günter Höglinger, MD, Professor at the German Center for Neurodegenerative Disorders in Munich and probably the world’s leading clinical researcher in PSP, organized an international effort to revise the criteria. I’m privileged to serve on the four-person Steering Committee. A year ago we started to hash things out by email and conference calls, using the published articles on clinical features of PSP that use either autopsy or the NINDS-SPSP Criteria as a gold standard. The group, comprising 33 people from 11 countries, met in Munich on March 9 and 10 to turn our rough draft into a final version suitable for submission to a journal for peer review.
The new criteria recognize the various phenotypes of PSP. They are PSP-Richardson syndrome (about 55% of all PSP), PSP-parkinsonism (30%), PSP-frontal dementia (5%), PSP-ocular motor (1%), PSP- pure akinesia with gait freezing (1%), PSP-corticobasal syndrome (1%), PSP-progressive non-fluent aphasia (1%), and PSP-cerebellar (<1%). The remaining few percent are combinations of these or still-unrecognized forms.
The new criteria also delineate various “oligosymptomatic” or “prodromal” (the wording remains unsettled) forms, which may or may not develop into one of the diagnosable phenotypes. For example, there is now evidence that someone in the PSP age group with gradually progressive gait freezing for several years and a normal MRI, even without other abnormalities, will almost always prove to have PSP. The same is true for someone with bilateral rigidity and bradykinesia who fails to respond to levodopa and has some sort of nonspecific, undiagnosable visual symptoms or dizziness. Neither of these patients would satisfy the proposed new criteria for any of the PSP phenotypes, but they may still be worth identifying for inclusion in a longitudinal cohort study of people who are at risk of developing PSP. Our new criteria do that.
I’ll keep you updated.