Today’s post
was not my idea at all, it was the author of one of the papers who has drawn my
attention to the subject.
Genetic
studies are complicated and are not the sort of thing I would have chosen to
read, let alone write about, before starting this blog.
The optimal time to initiate pharmacological
intervention in Autism?
However, much of the complex subject matter
has now already been covered, step by step, in earlier posts. Regular readers
should not feel put off.
It is
perhaps easier to think about ion channel dysfunctions, or channelopathies. Some of the key genetic dysfunctions produce
these channelopathies. There are many
posts in this blog about channelopathies, partly because many therapies already
exist to treat them.
Then we have
the complex signaling pathways which are often the subject of cancer research,
but we have seen that certain ones like RAS and PTEN are key to conditions like
some autism and some MR/ID.
So it is not
a big leap therefore to consider the findings of a statistical reassessment of
the existing genome-wide association studies (GWAS).
As is often the case in medical science, it is the acronyms/abbreviations, like GWAS, that make it look more
complex than it really is.
If you only ever read one paper
about the genetics of autism, I suggest you make it this one.
Fortunately,
the conclusion from the genetic study really fits nicely with the clinical
studies reviewed on this blog and even my own first-hand experience of investigating
and treating my n=1 case of autism.
Knut,
the
Biometrician
It was Knut
who left a brief comment on this blog and, after a little digging, I was very
surprised how much a statistician/biometrician could figure out about autism, from re-analyzing
the existing genome-wide association studies (GWAS).
I think the Simons Foundation could
save themselves a decade or two by giving him a call.
The Research
For those
wanting the science-lite version, there is a short article reviewing the research
in lay terms:-
“Hence,
modulation of ion channels in children at the age of about 12 months, when the
first symptoms of autism can be detected, may prevent progression to the more severe
end of the spectrum.” .
The actual research paper is here:-
You may find
it heavy going and I have highlighted some key parts.
“Despite evidence for a likely involvement of de novo and
environmental or epigenetic risk factors, including maternal antibodies or
stress during pregnancy and paternal
age, we contend that coding variations contribute substantially to the
heritability of ASD and can be successfully detected and assembled into
connected pathways with GWAS—if the experimental design, the primary outcome,
the statistical methods used, and the decision rules applied were better
targeted toward the particulars of non-randomized studies of common diseases.”
The data comes from the Autism Genome
Project (AGP), and there are two sets of data AGPI and AGPPII.
The third data set is for Childhood
Absence Epilepsy (CAE)
What I would call Classic Autism,
others call severe autism or autistic disorder; Knut calls it Strict Definition
Autism (SDA). HFA is high functioning
autism, much of which is Asperger’s Syndrome.
“Study design We aimed at risk factors specific to strict definition autism (SDA) by
comparing case subpopulations meeting the definition of SDA and milder cases
with ASD (excluding SDA), for which we here use the term ‘highfunctioning
autism’ (HFA). To reduce variance, we included only subjects of European
ancestry genotyped on the more frequently used platform in either stage. In AGP
II, we also excluded female cases because of confounding between chip platform
and disease severity. The total number of subjects included (m: male/f: female)
was 547/98 (SDA) and 358/68 (HFA) in AGP I and 375 (SDA) and 201 (HFA) in AGP
II.
Overall, the results (see Supplementary Figure 1 for a
Manhattan plot) are highly consistent with previously proposed aspects of the
etiology of ASD. The clusters of genes implicated in both of the independent
stages (Figure 2a/b) consistently overlap with our published CAE results
(Figure 2c), confirming
the involvement of ion channels (top right) and signaling downstream of RAS
(bottom left), with two noticeable additional gene clusters in
ASD. Both stages implicate several genes involved in deactivation of growth
factor (GF) receptors (Figure
2a/b, top left) as ASD-specific risk factors and chloride (Cl − ) signaling, either through Ca2+ activated
Cl− channels
Click to enlarge the figure
A new term is PTPR (protein
tyrosine phosphatases receptor), just to confuse us it is also called RPTP.
For example, the receptor protein tyrosine
phosphatases gamma (PTPRG) and zeta (PTPRZ) are expressed primarily in the
nervous system and mediate cell adhesion and signaling events during
development.
In an
earlier post I highlighted the numerous dysfunctions in growth factors (GF) in
autism. Knut is highlighting here the
effect of PTPR on growth factors. Later it
is suggested that this cascade of GF dysfunctions could be halted,
pharmacologically if it was identified very early. But, as Courchesne from UC San Diego noted,
by the time people have been identified as having autism, around three years
old, the accelerated brain growth has already run its course.
You would
need to intervene around one year old.
Broad evidence for involvement of PTPRs One of the most striking
observations is the involvement of at least five PTPRs in ASD (Figure 2,
10 o’clock position). PTPRs
(Table 1e) regulate GF signaling through reversible protein tyrosine
dephosphorylation.72 PTPRT (90th/20th, 8.57) was implicated in ASD by a
deletion73 (Table S2 AU018704) and a somatic mutation
It was my
post pondering the reasons for the positive effect of potassium supplementation
that drew Knut’s attention to this blog.
Now we move on to Knut’s ideas on potassium and chloride channels.
K+ and Cl− ion channels
as drug targets
Aside from PTPRs (Figure 2, 10 o’clock) as a risk factor for
protracted GF signaling, our
results suggest a second functional cluster of genes, involved in Cl− transport
and signaling, as specific to ASD (Table 1f). In AGP I, the CaCCs ANO4
and ANO7 scored 1st and 70th, respectively. In AGP II, the lysosome membrane H+
/Cl- exchange transporter CLCN7 scored 21st, followed by CAMK2A, which
regulates ion channels, including anoctamins82 (55th), and LRRC7 (densin-180),
which regulates CAMK2A83 (Figure 2a/b, 2 o’clock). The role of the anoctamins
in pathophysiology is not well understood, except that CaCC activity in some
neurons is predicted to be excitatory84 and to have a role in neuropathic pain
or nerve regeneration. More recently, CaCCs have also been suggested as involved
in ‘neurite (re)growth’. Finally,
we compared the HFA and SDA cases as separate groups against all parental
controls in the larger AGP I population. Overall, the level of
significance is lower and the enrichment is less pronounced, especially for the
SDA cases (Supplementary Figure 9), as expected when cases and some controls
are related. For the HFA cases (Figure 4, and Supplementary Figure 8), however,
a second anoctamin, ANO2, located on the other arm of chromosome 12, competes
with ANO4 (Figure 1, left), for the most significant gene among the result.
Hence, drugs targeting
anoctamins might have broader benefits for the treatment of ASD than in
preventing progression to more severe forms of autism. ANO2 and ANO6 are
associated with panic disorder and major depressive disorder, respectively.
ANO3, ANO4, ANO8 and ANO10, but not ANO1, are also expressed in neuronal
tissue.86 As ‘druggable
channels’, anoctamins ‘may be ideal pharmacological targets to control
physiological function or to correct defects in diseases’. Few drugs, however, target individual anoctamins
or even exclusively CaCCs. Cl−
channel blockers such as fenamates, for instance, may decrease neuronal
excitability primarily by activating Ca2+-dependent outward rectifying K+
channels.
Here is a
follow-up paper with consideration of the possible next steps.
Gene gene environment behavior development
interaction at the core of autism:
Here, we combine a recent wide-locus approach with novel
decision strategies fine-tuned to GWAS. With these methodological advances,
mechanistically related clusters of genes and novel treatment options,
including prevention of more severe forms of ASD, can now be suggested from
studies of a few hundred narrowly defined cases only.
(Nonsyndromic) autism starts with largely unknown prenatal
events (♂: age, ♀: virus/stress ...)
• Mutations in growth factor regulators (PTPRs) lead to
neuronal overgrowth (brain sizes).
• Mutations in K+/Cl− channels cause Ca2+ mediated over excitation
of neurons (“intense world”).
• Stressful environments (urbanization) contribute to
epistatic interaction (increasing prevalence).
• This GGE interaction causes “migraine-like” experiences
during the “stranger anxiety” period where children learn verbal/social skills,
leading to behavioral maladaptation (“tune-out”).
• The
lack of verbal/social stimuli causes “patches of disorganization” (Stoner 2014,
NEJM) as a form of developmental maladaptation when underutilized brain areas
are permanently “pruned”. The PTPRs point to a short window of
opportunity (WoO) for pharmacological intervention:
• Treatment has to begin as early as possible, while neurons
are still growing (12 months of age. Broad support for the proposed unifying
etiology and the 2nd year of life as the WoO:
• Regression (“loss of language”) seen in some children
>12 mos of age.
• “Patches of disorganization” in >2 yr old brains.
• Romanian orphans developed “quasi-autism” when placed into
foster care at >24 mos of age.
• Hearing impairment leading to intellectual
disability when diagnosed >24 mos of age.
A rational drug target: treating
either of two epistatic risk factors suffices:
• Blocking growth factors
(Gleevac, ...) is unacceptable in children merely at risk of ASD.
• Ion channel
modulators have been used in small children for arthritis and seizures.
Here is a response
to Knut’s first paper from a professor at the UCLA medical school who suggests
the combination of the specific NSAID and bumetanide.
The
professor would better understand the mechanism of action of bumetanide in autism if
he read Ben Ari’s research more thoroughly, or even this blog.
The article by Wittkowski et al.1 reports results of human genetic studies that suggest that a nonsteroidal
anti-inflammatory drug (NSAID) given for a few months from the time of the
first symptoms might help some children who are at risk of developing more
severe forms of atrial septal defect.
While the authors mention the recent article by Lemonnier et al.,2 which reported that a clinical study of the
diuretic Bumetanide was partially effective in children with milder forms of autism,
they seem to have overlooked that these two treatments may well be
complementary, leading to sequential interventions, each targeting specific
risks related to well-defined stages in the development of brain and social
interactions.
Since abnormal
brain development in autistic disorder goes through different stages from
infancy to childhood, targeting different developmental stages with different
treatment interventions may well be necessary to foster continued normalization
of brain growth.
Bumetanide is known to block inward chloride
transporters, yet the relation of this mechanism to the etiology of autism is
unknown. Wittkowski et al. identified mutations
in calcium-activated (outward) chloride channels as associated with autistic
disorder, suggesting loss-of-function mutations in anoctamins as one of the
risk factors for autism. This provides a testable hypothesis for the mechanism
by which Bumetanide alleviates symptoms of autism. For example, mouse models
could test whether Bumetanide ameliorates a stress-induced phenotype caused by
a knockout/down in ANO2 and/or ANO4.
A second
cluster of genes identified receptor protein tyrosine phosphatases, which
downregulate growth factors. These findings support the notion that successful
treatment should start as early as possible,3 while neuronal development still takes place.
The rationale for combining these two treatments rests
on the fact that Bumetanide is contraindicated in infancy because it is known
to interfere with neuronal development when used long term. In contrast, the
NSAID proposed in the second study has been given for decades to children with
juvenile idiopathic arthritis from 6 months of age on, with no adverse effects
on brain development. It is known to modulate chloride channels (see above) as
well as potassium channels.4
In conclusion,
I wish to extend their hypothesis based on the synergy of the two treatment
approaches: (1) early treatment with NSAID can reduce early maladaptive
behaviors that cause abnormal pruning of neurons in the cortical areas; (2)
these children could subsequently benefit from Bumetanide, which would
compensate for the primary ion channel defect, but could not reverse the
secondary effect of abnormal pruning.
This hypothesis allows for a
novel two-way interaction between behavior and molecular events. Traditionally,
one assumes that molecular events determine behavior. The new hypothesis, based
on human genetics, also allows for symptoms (such as the absence of social
interactions, delayed speech onset and language development) during certain
sensitive periods to change molecular events (pruning of neurons in areas
required for normal development).
Therapeutic implications from the
genetic analysis
Some of the
therapies that Knut is proposing, based on the genetic analysis, have already
been reviewed in this blog. Some have
not. A few therapeutic ideas in this
blog actually target genes Knut has identified, but not highlighted a therapy.
I will just
review the drugs and genes that the above study highlights.
Benzodiazepines
Low dose
clonazepam fits in this category. We
have the work of Professor Catterall to support its use. At higher doses, benzodiazepines have
different effects but use is associated with various troubling side effects.
Bumetanide
Bumetanide
is at the core of my suggested therapy for classic autism or what Knut calls
SDA (strict definition autism). We have
Ben-Ari to thank for this
Fenamates (ANO 2/4/7 & KCNMA1)
Here Knut is
trying to target the ion channels expressed by the genes ANO 2/4/7 &
KCNMA1.
·
KCNMA1
is a calcium activated potassium channel.
KCNMA1 encodes the ion channel KCa1.1,
otherwise known as BK
(big potassium). This was the subject of
post that I never got round to publishing.
Fenamates
are an important group of clinically
used non-steroidal anti-inflammatory drugs (NSAIDs), but they have other
effects beyond being anti-inflammatory.
They act as CaCC inhibitors and also stimulate BKCa channel activity.
“The
fenamates can stimulate BKCa channel activity in a manner that seems to be
independent of the action of these drugs on the prostaglandin pathway”
“Of this “first
generation” of CaCC inhibitors, NFA (a fenamate called niflumic acid) is the most potent blocker of these channels
and the compound most frequently used to investigate the physiological role of
CaCCs”
Choice of Fenamate
There are several fenamate-type NSAIDs, but one is a
very well used generic drug, Mefenamic acid known as Ponstan, Ponalar, Ponstyl, Ponstel and other
generic names. It is even available as a
syrup for children.
It is not
available in all countries.
Gabapentin
Gabapentin is used primarily to treat seizures and neuropathic pain. It is also
commonly prescribed for many off-label uses,
such as treatment of anxiety disorders, insomnia, and bipolar disorder.
Some people
with autism are prescribed Gabapentin.
Some people suffer side effects and others do not.
If you have
a dysfunction of voltage operated calcium channels, Gabapentin should help.
Memantine
This is all
about modifying NMDA receptors. Memantine
is but one method.
Minocycline
Minocycline is an antibiotic with several little known extra properties.
In autism, we looked at its ability to reduce microglial activation and
so improve autism. A clinical trial
showed that it did not help autism.
Minocycline
also affects MMP-9. MMP-9 is an enzyme found to be associated with numerous pathological processes,
including cancer, immunologic and cardiovascular diseases.
“ The
results of this study suggest that, in humans, activity levels of MMP-9 are
lowered by minocycline and that, in some cases, changes in MMP-9 activity are
positively associated with improvement based on clinical measures.”
So if you are treating a case of Fragile-X, or partial "Fragile-X-like" autism, better take note.
Rapamycin
Rapamycin
and mTOR was the subject of the following post:
Both too much and too little mTOR can occur in autism.
Conclusion
My conclusion
is probably different to yours.
For me, it
seems that all the pieces really are fitting together and so this blog on the
cause and treatment of classic autism will eventually cover the current
scientific knowledge, in its entirety. No
complex areas are off limits, because in the end they are not as complex as they
seem, when you lift the veil of jargon and acronyms.
From the
all-important therapeutic perspective, new insights from today’s post are:-
·
Those
with a dysfunction of voltage operated calcium channels might want to give Gabapentin
(Neurontin) a try.
·
The
fenamate-type NSAID mefenamic
acid, widely
known as Ponstan,
really should be tested, either at home, or in a clinical trial.
This statistical analysis is based on “all autism”, so
any one person would be highly unlikely to have all the mentioned
dysfunctions. These are the most common genetic
dysfunctions and many can both hypo and hyper, as in the case of NMDA
dysfunctions and indeed mTOR.
In Knut’s chart, I would add a green line pointing to RAS
and PTEN with the word Atorvastatin. Baclofen
would point to the growth factors.
Verapamil would point in multiple places.
The motto of University
of Tübingen, where Knut originally comes from, is Attempto ! The Latin for "I dare".
This might be a useful
motto for readers of this blog, and also a good tittle for a book on treating
autism.
