Autism regression around aged 9-18 years old – is it catatonia?

 

From the title of today’s post you can see that this is one for parents of older children and indeed some adults. I should add that personally I am not a fan of observational diagnoses like catatonia, because I am interested in the biological cause of the unwanted behaviors, as a means to find effective therapy. Catatonia is a very broad term, but in current psychiatry that is what we have.

I was recently contacted by a mother whose adolescent son had regressed severely and she wanted to know what she had done wrong. She had not done anything wrong of course. Now she has to figure out what triggered the changes and how to reverse them. Catatonia is one possibility and it has not been covered in this blog.

The word catatonic drifted into casual English. Today, people use it informally to describe anyone who is completely unresponsive, frozen, or motionless.

As a medical term a diagnosis of catatonia is typically confirmed when an individual displays three or more of the following features:

Stupor & Mutism. Profound unresponsiveness to the outside world, along with a lack of, or severely reduced, speech.

Catalepsy & Waxy Flexibility. The tendency to passively hold bizarre, fixed postures against gravity or to maintain a position exactly as it is set by someone else.

Negativism. An active or passive resistance to instructions or movement.

Posturing. The spontaneous holding of unnatural, active postures for long periods.

Stereotypy & Mannerisms. Repetitive, non-goal-directed movements (such as rocking or pacing) or odd caricatures of normal actions.

Excitement/Agitation. Frenzied or purposeless motor activity that does not seem influenced by external stimuli.

Echolalia & Echopraxia. The involuntary mimicking of someone else's speech or movements.

 

Catatonia often occurs in people with schizophrenia, bipolar, or major depressive disorders. It can also be triggered by autoimmune diseases, brain injuries, or even severe infections. About 10% of people with autism will develop symptoms of catatonia. It can affect any level of autism.

Puberty can be the trigger for catatonia, but it can also develop much later in adulthood. 

Diagnosing catatonia looks different depending on the patient's age. For instance children are much more likely to present with refusal to eat or drink and mutism, which caregivers sometimes mistake for stubbornness or behavioral issues.

Autism-related catatonia can manifest differently than it does in non-autistic populations. It is often characterized by a distinct pattern of gradual, late regression rather than a sudden, acute physical freeze.

The "Late Regression" Timeline

While autism is usually diagnosed in early childhood, catatonia typically hits during adolescence or early adulthood.

The Early Warn Signs (Ages 10–14) Before full-blown catatonia develops, young teens with autism often exhibit a gradual increase in obsessive-compulsive routines, extreme physical slowness, or brief episodes of "freezing".

Full Onset (Ages 15–19) Full-syndrome catatonia typically solidifies during the peak of pubertal development. It is rare to see the full syndrome in autistic children under the age of 15.

Unique symptoms in autistic individuals

Because symptoms overlap with common autistic traits, catatonia can be difficult to recognize.

Loss of Function (Severe Regression). A sudden or progressive inability to complete daily activities they previously mastered (e.g., getting dressed, bathing, or using utensils).

Severe "Freezing" and Stuckness. Getting physically stuck mid-motion—such as freezing in a doorway or holding a cup halfway to their mouth for minutes.

The "Shutdown" Phenomenon. Severe passivity where the individual stops talking (mutism), avoids all eye contact, and refuses to eat or drink.

Hyperactive and Self-Injurious Behaviors. Rather than just freezing, autistic individuals frequently display hyperactive catatonia, which includes repetitive, automatic, and severe self-injury (like severe head-banging) that is unrelated to communicative distress.

Fluctuation Symptoms are notoriously variable—an individual may seem heavily affected or locked in place in the morning but move relatively normally by evening.

 

Why does it happen?

In autism, catatonia is frequently triggered by extreme environmental stress, major life transitions (like leaving school), trauma, severe anxiety, or co-occurring mood disorders.

 

Biological drivers

While psychological and environmental stress (such as extreme anxiety, bullying, or major routine changes) frequently act as the spark, catatonia is ultimately a neurological breakdown. The primary biological triggers, chemical imbalances, and genetic factors that cause the brain to enter a catatonic state include:

1.     Neurotransmitter imbalances

The most widely accepted biological explanation for catatonia is a sudden, severe imbalance of chemical messengers in the brain circuits that control movement and behavior:

·        GABA Deficit: GABA is the brain's primary calming/inhibitory neurotransmitter. In catatonia, there can be a sudden drop in GABA-A receptor activity. Because the brain loses its ability to regulate or slow down signals, motor pathways lock up. This explains why benzodiazepines (which increase the sensitivity to a given amount of GABA) can often rapidly reverse the condition.

·        Glutamate Overdrive: Glutamate is an excitatory chemical. A spike in glutamatergic activity, specifically involving NMDA receptors, can overstimulate the brain's motor networks, forcing the body into fixed, rigid postures.

·        Dopamine Drop: A sudden drop in dopamine activity—specifically at D2 receptors—paralyzes the brain’s reward and movement centers. This mimics the chemical state seen in Parkinson's disease, creating severe physical slowness or total immobility.

 

2.     Neuroimmune and autoimmune triggers

The immune system can directly attack the brain, causing acute neuroinflammation that triggers catatonia.

·        Autoimmune Encephalitis: Conditions like anti-NMDA receptor encephalitis occur when the body mistakenly produces autoantibodies that attack NMDA receptors in the brain. Catatonia is a primary symptom in up to 70% of these cases.

·        Systemic Infections: In medically vulnerable or autistic individuals, severe underlying infections (like a urinary tract infection, pneumonia, or a severe viral illness) can trigger a massive cytokine response. This inflammation breaches the blood-brain barrier, disrupting motor circuits and inducing catatonic behavior.

 

3.     Structural brain differences

Neuroimaging studies show that catatonia often stems from communication failures within specific brain loops (the cortico-striato-thalamo-cortical circuits) which govern motor planning.In autistic individuals with catatonia, MRI scans frequently reveal abnormally small cerebellar structures. Because the cerebellum is responsible for fine-tuning motor actions and smooth coordination, these structural differences make the motor loop highly vulnerable to completely breaking down under stress.

4.     Genetic susceptibility

Catatonia can have a hereditary link. Genetic studies on families with a vulnerability to periodic catatonia have identified specific genetic alterations. Interestingly, susceptibility regions on chromosomes 15 and 22 are heavily implicated in both autism and catatonia, suggesting a shared genetic architecture that primes certain individuals for the condition.

5.     Medication effects & withdrawal

Abrupt biological shifts caused by pharmaceutical substances can paralyze the motor system:

·        Dopamine Blockers: Exposure to strong antipsychotic medications can sometimes block dopamine receptors so aggressively that it induces catatonia .

·        Sedative Withdrawal: Suddenly stopping medications that calm the central nervous system (such as benzodiazepines or barbiturates) causes a rebound biological shock, stripping away the brain’s chemical brakes and inducing a catatonic freeze. Always taper the dosage.

  

Mainstream therapy for catatonia 

The treatment goal is to resolve any physical freezing first, then address the underlying psychiatric or medical cause.

Clinicians use a strict, stepped protocol ranging from medications to medical procedures. The first-line medication is Lorazepam (Ativan), a benzodiazepine. Lorazepam increases GABA-A activity, restoring the brain's missing chemical brakes. Intravenous Lorazepam is given to confirm the diagnosis if symptoms improve rapidly.

Electroconvulsive therapy (ECT) is the definitive treatment for severe cases. ECT is deployed if a patient shows no improvement after intensive Lorazepam trials. ECT is performed safely in a hospital setting under general anesthesia and muscle relaxants.

Maintenance Therapy: Long-term, periodic ECT may be required for individuals with chronic conditions.

Second-line options include glutamate antagonists like Amantadine or Memantine, if first-line choices fail. Alternative GABA agents like Zolpidem (Ambien) are sometimes utilized to break treatment-resistant freezing. Medications to Avoid: Traditional dopamine-blocking antipsychotics (like haloperidol) are generally not useful. Antipsychotics can worsen the motor paralysis or trigger Neuroleptic Malignant Syndrome.

 

Peter’s thought’s on mainstream therapy

The 30+% of level 3 autism who respond to bumetanide would have an extreme negative (paradoxical) reaction to Lorazepam (Ativan). They would get very aggressive and “go nuts.”

In most countries ECT is highly regulated. It clearly is effective for some people, but it looks a rather crude therapy to me.

The mainstream therapies look very “thin” to me. I think much more should be possible.  

I think the term catatonia is much too vague and you need to know why these changes have occurred, then you can figure out a therapy.

PANS can trigger the symptoms of catatonia. In many counties PANS is still not recognized as a diagnosis. PANS (Pediatric Acute-onset Neuropsychiatric Syndrome) would not respond to a benzodiazepine drug like Lorazepam, but would instead require immunotherapy, which is completely different.

As usual we come back to getting an observational like catatonia, autism or trendy new ones like ARFID (picky eating) is just the first step in the process. Then you need to find out why? What biological or behavioral factors are driving these symptoms. Then you can figure out how to treat them, or indeed choose not to treat them, if you are so inclined.

  

Could it be OCD rather than catatonia?

One reason catatonia can be difficult to recognize in autism is that several of its symptoms overlap with severe obsessive-compulsive disorder (OCD). In fact, some studies have found that obsessive-compulsive symptoms are very common in autistic individuals who later develop catatonia.

Parents often report that their child begins:

• Writing the same words repeatedly
• Talking about the same topics over and over
• Performing increasingly rigid rituals
• Becoming distressed when routines are interrupted
• Withdrawing socially

These symptoms may point to OCD, catatonia, or a combination of both.

The key distinction is that OCD is driven by obsessions and compulsions, whereas catatonia is characterized by a loss of initiative and a decline in function. An autistic teenager with OCD may be extremely active in performing rituals, while a teenager with catatonia may become progressively slower, less spontaneous, and increasingly "stuck."

Questions that may help distinguish the two include:

• Does the person become anxious if prevented from performing the behavior?
• Are they physically slower than before?
• Do they need prompting to start everyday activities?
• Have they lost skills they previously mastered?
• Are they spending long periods inactive or frozen?

The two conditions can coexist. In some cases, severe OCD may precede the development of catatonia.

Investigations

When a child, teenager, or adult with autism experiences a significant regression after years of relative stability, it is worth looking beyond the autism diagnosis itself.

One investigation I would seriously consider is an EEG (electroencephalogram). Epilepsy or "just" abnormal electrical activity in the brain can sometimes present as:

• Regression
• Social withdrawal
• Changes in communication
• Cognitive decline
• Repetitive behaviors
• Episodes of staring or unresponsiveness

Several studies have reported higher rates of epilepsy among autistic individuals who develop catatonic symptoms.

An EEG may not identify the cause of the regression, but it is a relatively straightforward way to investigate an important and potentially treatable neurological contributor.

Other investigations may include:

• Sleep assessment
• Review of medications
• Assessment for OCD and anxiety disorders
• Evaluation for depression
• Screening for autoimmune or inflammatory conditions where clinically indicated

The important point is that autism itself is not usually a progressive condition. When someone loses skills after years of stability, it is worth asking what has changed and whether there is a treatable condition contributing to the decline.

 

High dose L-Serine to treat children under 7 with severe autism + ID ? It works in Korea

 

Source: Joon Kyu Park, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons

 

Today’s post is a follow up to the recent one that showed Memantine was beneficial to people with level 1 autism, normal IQ, with ADHD and anxiety/depression.

Our reader Hoang, highlighted a recent trial in Korea that used the OTC supplement L-serine, which has a biological effect that is the opposite of Memantine. The trial is part of series looking at treating those with severe autism with ID (intellectual disability). 

High-dose L-serine has been tested in children with severe autism and intellectual disability, and the main benefits were seen in those under 7 years old. While it may work by boosting NMDA receptor activity through conversion to D-serine, other brain-supporting roles of L-serine—like helping neuron membranes and reducing stress on brain cells—could also contribute. Older children may not respond as well, possibly because their brains are less plastic or they convert less L-serine to D-serine. Researchers should now explore whether direct D-serine dosing might help older kids, but safety must be considered.

 

The Trials and Target Group

The trials of AST-001, a syrup formulation of L-serine, focused on children with severe autism and intellectual disability (ID). The phase 2 study included children aged 2–11, but the most pronounced improvements were in those under 7 years old. The benefit did not entirely disappear after age 7, but it was smaller and harder to measure.

Dosing was weight-tiered:

Weight (kg)	Dose (g, twice a day)
10–13	2
14–20	4
21–34	6
35–49	10
>50	14

The outcomes measured were adaptive behavior (Vineland Adaptive Behavior Scales II) and clinical global impressions, with high-dose L-serine showing a statistically significant improvement over placebo.

 

How L-Serine Might Work

1. NMDA Receptor Modulation

L-serine can be converted in the brain to D-serine, a co-agonist of NMDA receptors, which are critical for learning, memory, and social behavior. This mechanism aligns with the idea that boosting NMDA signaling could help in some autism. This is the exact opposite of what Memantine does.

2. Other Neuroprotective Roles

However, L-serine also supports:

• Phospholipid and myelin synthesis, crucial for neuron structure
• One-carbon metabolism and methylation, which help maintain healthy brain chemistry
• Reducing cellular stress, oxidative damage, and excitotoxicity
• L-serine is the precursor to glycine. This matters because glycine is also an NMDA co-agonist (alongside D-serine). In some brain regions glycine—not D-serine—is the primary co-agonist.

So, the clinical effect might not be solely through NMDA receptor modulation.

 

Why Benefits Are Seen Mainly in Children Under 7

Several factors may explain the age effect:

1.     Brain Plasticity – Younger brains are more adaptable, so interventions may show stronger effects.

2.     Conversion to D-serine – L-serine is converted to D-serine by serine racemase, and this may be less efficient in older children.

3.     Ceiling Effects – In older children with long-standing autism and ID, neural circuits may have already stabilized in ways that make observable behavioral improvements harder.

It is unclear whether older children truly cannot benefit, or if the benefit is harder to measure with standard adaptive behavior scales.

 

Could D-Serine Directly Help Older Children?

A hypothesis is that older children might need higher levels of D-serine than their bodies can produce from L-serine. In theory:

• Direct D-serine supplementation might overcome this bottleneck.
• Safety is the main concern, as excessive D-serine can stress kidneys or neurotransmitter systems.

No large trials have tested this yet in older children with autism.

About the Researcher

Dr Yoo-Sook Joung led the AST-001 trials. She is a psychiatrist with an interest in autism interventions and has explored approaches like animal-assisted therapy. While not a basic science researcher, her clinical insights have helped design practical trials in children with severe autism and ID.

Takeaways

• High-dose L-serine shows promising results in children under 7 with severe autism and ID. The low dose was not effective.
• Benefits may involve NMDA receptor modulation, but other neuroprotective effects are likely relevant.
• Older children may require alternative approaches (e.g., D-serine), but evidence is lacking.
• Safety and careful dosing are essential; trials so far show good tolerability, with diarrhea being the most common side effect.

 

Here is the associated research leading up the recent trial

Population Pharmacokinetic Model of AST-001, L-Isomer of Serine, Combining Endogenous Production and Exogenous Administration in Healthy Subjects

AST-001 is an L-isomer of serine that has protective effects on neurological disorders. This study aimed to establish a population pharmacokinetic (PK) model of AST-001 in healthy Korean to further propose a fixed-dose regimen in pediatrics. The model was constructed using 648 plasma concentrations from 24 healthy subjects, including baseline endogenous levels during 24 h and concentrations after a single dose of 10, 20, and 30 g of AST-001. For the simulation, an empirical allometric power model was applied to the apparent clearance and volume of distribution with body weight. The PK characteristics of AST-001 after oral administration were well described by a two-compartment model with zero-order absorption and linear elimination. The endogenous production of AST-001 was well explained by continuous zero-order production at a rate of 0.287 g/h. The simulation results suggested that 2 g, 4 g, 7 g, 10 g, and 14 g twice-daily regimens for the respective groups of 10–14 kg, 15–24 kg, 25–37 kg, 38–51 kg, 52–60 kg were adequate to achieve sufficient exposure to AST-001. The current population PK model well described both observed endogenous production and exogenous administration of AST-001 in healthy subjects. Using the allometric scaling approach, we suggested an optimal fixed-dose regimen with five weight ranges in pediatrics for the upcoming phase 2 trial.

  

Population pharmacokinetic and pharmacodynamic model guided weight-tiered dose of AST-001 in pediatric patients with autism spectrum disorder

AST-001, a novel syrup formulation of L-serine, was developed for the treatment of autism spectrum disorders (ASD) in pediatric patients. This study aimed to establish a pharmacokinetic (PK)-pharmacodynamic (PD) model to elucidate the effect of AST-001 on adaptive behavior in children with ASD. Due to the absence of PK samples in pediatric patients, a previously published population PK model was used to link the PD model by applying an allometric scale to body weight. The time courses of Korean-Vineland Adaptive Behavior Scale-II Adaptive Behavior Composite (K-VABS-II-ABC) scores were best described by an effect compartment model with linear drug effects (Deff, 0.0022 L/μg) and linear progression, where an equilibration half-life to the effect compartment was approximately 15 weeks. Our findings indicated a positive correlation between the baseline K-VABS-II-ABC score (E0, 48.51) and the rate of natural progression (Kprog, 0.015 day⁻¹), suggesting enhanced natural behavioral improvements in patients with better baseline adaptive behavior. Moreover, age was identified as a significant covariate for E0 and was incorporated into the model using a power function. Based on our model, the recommended dosing regimens for phase III trials are 2, 4, 6, 10, and 14 g, administered twice daily for weight ranges of 10–13, 14–20, 21–34, 35–49, and >50 kg, respectively. These doses are expected to significantly improve ASD symptoms. This study not only proposes an optimized dosing strategy for AST-001 but also provides valuable insights into the PK-PD relationship in pediatric ASD treatment.

 

AST‐001 versus placebo for social communication in children with autism spectrum disorder: A randomized clinical trial

Aim

This study examined the efficacy of AST‐001 for the core symptoms of autism spectrum disorder (ASD) in children.

Methods

This phase 2 clinical trial consisted of a 12‐week placebo‐controlled main study, a 12‐week extension, and a 12‐week follow‐up in children aged 2 to 11 years with ASD. The participants were randomized in a 1:1:1 ratio to a high‐dose, low‐dose, or placebo‐to‐high‐dose control group during the main study. The placebo‐to‐high‐dose control group received placebo during the main study and high‐dose AST‐001 during the extension. The a priori primary outcome was the mean change in the Adaptive Behavior Composite (ABC) score of the Korean Vineland Adaptive Behavior Scales II (K‐VABS‐II) from baseline to week 12.

Results

Among 151 enrolled participants, 144 completed the main study, 140 completed the extension, and 135 completed the follow‐up. The mean K‐VABS‐II ABC score at the 12th week compared with baseline was significantly increased in the high‐dose group (P = 0.042) compared with the placebo‐to‐high‐dose control group. The mean CGI‐S scores were significantly decreased at the 12th week in the high‐dose (P = 0.046) and low‐dose (P = 0.017) groups compared with the placebo‐to‐high‐dose control group. During the extension, the K‐VABS‐II ABC and CGI‐S scores of the placebo‐to‐high‐dose control group changed rapidly after administration of high‐dose AST‐001 and caught up with those of the high‐dose group at the 24th week. AST‐001 was well tolerated with no safety concern. The most common adverse drug reaction was diarrhea.

Conclusions

Our results provide preliminary evidence for the efficacy of AST‐001 for the core symptoms of ASD.

 

The what, when and where of treating autism

The human brain is a work in progress up until your mid 20s.

It is near adult-sized at the age of 5, but many key developmental processes remain.

As brain development goes through it various steps, it requires certain genes to be activated to produce specific proteins. This is why in some single gene autisms babies are born appearing entirely typical, because at that point they are typical. Shortly thereafter when the gene cannot produce enough of its protein (haploinsufficiency) things start developing off-track. The human body is highly adaptable and the brain keeps on changing, but now on a different track.

Many dysfunctions in autism are localized to just one part of the brain and indeed you can have the opposite dysfunction in different parts of the brain at the same time. Some dysfunctions can be just transitory, or indeed just extreme in one particular developmental window.     

When it comes to NMDA activity we know that very often in autism and schizophrenia it is disturbed. But, it can be too much or too little (hyper/hypo) and very likely this changes over time and varies in different parts of the brain.

Viewed in this broader context, it is not odd to see an intervention that is most effective up to the age of seven.

  

Conclusion

If you know a child with severe autism and intellectual disability, who is under 7 years old, maybe suggest to the parents to investigate following our proactive reader Hoang and make a trial of the OTC supplement L-Serine. You can buy it inexpensively on-line, just search “L serine bulk powder.” In the US 1kg costs about $50. Just follow the dosage in the trials.

L-serine is very safe.

Using D-serine is more problematic. In clinical studies for schizophrenia and cognitive disorders, doses ranged from 30 mg/kg/day to 120 mg/kg/day in divided doses. D-serine is mostly safe at moderate doses, but very high doses carry risks of kidney stress and excitotoxicity.

Modest amounts of L-serine can be found in eggs, chicken, milk etc. The body then converts this to D-serine using an enzyme called serine racemase and vitamin B6. Once these are used up, no more D-serine can be produced “naturally.” This is why schizophrenia researchers use D-serine itself. D-serine is also sold as a bulk OTC supplement.

If the child was actually an undiagnosed Memantine-responder, you would expect to see the following if they took high dose L-serine:

·        ↑ irritability

·        ↑ sensory overload

·        ↑ hyperactivity

·        ↑ emotional volatility

·        ↑ stereotypy

·        ↑ anxiety

Because a memantine responder is a child whose biology is defined by NMDA receptor overactivity, where excessive glutamate signalling drives irritability, sensory overload, anxiety, and cognitive stress and memantine works precisely because it reduces this hyper-NMDA state.

L-serine does the opposite, it increases D-serine and so enhances NMDA activity and so in an L-serine responder it improves:

·        learning and cognitive processing

·        social attention and engagement

·        adaptive behaviour

·        overall developmental trajectory

 

In this group, the core bottleneck is not excessive glutamatergic activity but insufficient NMDA co-agonism, especially in early development when social circuits and sensory-integration networks are still forming.

 

What does “insufficient NMDA co-agonism” mean?

NMDA receptors do not work like simple on/off switches.

They need two keys to open:

·        Glutamate – the main excitatory neurotransmitter

·        A co-agonist – either D-serine or glycine

If glutamate is present but the co-agonist is missing or too low, the NMDA receptor cannot fully activate, even though the neuron is trying to fire normally.

This situation is called NMDA hypofunction caused by insufficient co-agonism

In plain terms, the glutamate system is not actually weak. The receptor is not working properly because the “second key” is missing.

 

Neural circuits needed for learning, plasticity, and social behaviour do not work properly, because the key is missing. Go find it!

   

Why does this matter in autism with ID?

Several studies (postmortem, CSF, MR spectroscopy) show that in many children with severe autism + language delay + ID, D-serine levels are reduced in key brain areas (prefrontal cortex, temporal cortex, hippocampus).

Possible reasons:

·        Low activity of serine racemase (the enzyme converting L-serine → D-serine)

·        Higher breakdown of D-serine by DAO (D-amino acid oxidase)

·        Developmentally immature astrocytes (which supply D-serine early in life)

·        Genetic factors affecting NMDA co-agonist pathways

When D-serine is low, NMDA receptors cannot activate normally even if glutamate levels are normal or high.

 

The result:

Cognitive delay, poor adaptive behaviour, weak learning reinforcement, sensory disturbances, and poor social reciprocity.

How does L-serine help?

·        L-serine is the precursor to D-serine.

 

By giving large doses of L-serine

·        The brain produces more D-serine

 

D-serine binds the NMDA co-agonist site

·        NMDA receptors can finally reach normal activation

·        Neural circuits can strengthen and rewire more effectively

·        Behaviour improves, especially in younger children where plasticity is high

 

This is why L-serine produces the opposite clinical effect of memantine:

 

• Memantine helps when NMDA activity is too high

• L-serine helps when NMDA activity is too low because of a missing co-agonist

ARBs and ACE inhibitors for Autism, an old Peter idea finally explored in a research model

 

 A home run? Certainly worth further consideration. 

When I was doing my review of unexplored potential autism therapies several years ago, I did look at two closely related classes of drugs. ARBs and ACE inhibitors.

I wrote about it in blog posts and set out why I thought the ARB telmisartan was the best one to trial first.

 

           Targeting Angiotensin in Schizophrenia and Some Autism          

Just when you thought we had run out hormones to connect to autism and schizophrenia, today we have Angiotensin.

Angiotensin is a hormone that causes vasoconstriction and a subsequent increase in blood pressure. It is part of the renin-angiotensin system, which is a major target for drugs (ACE inhibitors) that lower blood pressure. Angiotensin also stimulates the release of aldosterone, a hormone that promotes sodium retention which also drives blood pressure up.

Angiotensin I has no biological activity and exists solely as a precursor to angiotensin II.

Angiotensin I is converted to angiotensin II  by the enzyme angiotensin-converting enzyme (ACE).  ACE is a target for inactivation by ACE inhibitor drugs, which decrease the rate of Angiotensin II production.  

It turns out that Angiotensin has some other properties very relevant to schizophrenia, some autism and quite likely many other inflammatory conditions. 

Blocking angiotensin-converting enzyme (ACE) induces those potent regulatory T cells that are lacking in autism and modulates Th1 and Th17 mediated autoimmunity.  See my last post on Th1,Th2 and Th17. 

In addition, Angiotensin II affects the function of the NKCC1/2 chloride cotransporters that are dysfunctional in much autism and at least some schizophrenia.

Then I wrote another post and made a trial of Telmisartan.

Angiotensin II in the Brain & Therapeutic Considerations

I was pleased to see that some researchers have recently published a paper on this subject. They chose an ACE inhibitor called Captopril.

 

Captopril restores microglial homeostasis and reverses ASD-like phenotype in a model of ASD induced by exposure in utero to anti-caspr2 IgG

Microglia play a crucial role in brain development, including synaptic pruning and neuronal circuit formation. Prenatal disruptions, such as exposure to maternal autoantibodies, can dysregulate microglial function and contribute to neurodevelopmental disorders like autism spectrum disorder (ASD). Maternal antibodies targeting the brain protein Caspr2, encoded by ASD risk gene Cntnap2, are found in a subset of mothers of children with ASD. In utero exposure to these antibodies in mice leads to an ASD-like phenotype in male but not in female mice, characterized by altered hippocampal microglial reactivity, reduced dendritic spine density, and impaired social behavior. Here, we studied the role of microglia in mediating the effect of in utero exposure to maternal anti-Caspr2 antibodies and whether we can ameliorate this phenotype. In this study we demonstrate that microglial reactivity emerges early in postnatal development and persists into adulthood following exposure in utero to maternal anti-Caspr2 IgG. Captopril, a blood-brain barrier permeable angiotensin-converting enzyme (ACE) inhibitor, but not enalapril (a non-BBB permeable ACE inhibitor) ameliorates these deficits. Captopril treatment reversed microglial activation, restored spine density and dendritic arborization in CA1 hippocampal pyramidal neurons, and improved social interaction. Single-cell RNA sequencing of hippocampal microglia identified a captopril-responsive subcluster exhibiting downregulated translation (eIF2 signaling) and metabolic pathways (mTOR and oxidative phosphorylation) in mice exposed in utero to anti-Caspr2 antibodies treated with saline compared to saline-treated controls. Captopril reversed these transcriptional alterations, restoring microglial homeostasis. Our findings suggest that exposure in utero to maternal anti-Caspr2 antibodies induces sustained neuronal alterations, microglial reactivity, and metabolic dysfunction, contributing to the social deficits in male offspring. BBB-permeable ACE inhibitors, such as captopril, warrant further investigation as a potential therapeutic strategy in a subset of ASD cases associated with microglial reactivity.

 

So here is an update that incorporates all these ideas and the new study.

 ___ 

Targeting the Brain Renin-Angiotensin System: From Schizophrenia to Autism (2025 Update)

By Peter Lloyd-Thomas, Epiphany ASD Blog

In 2017, I wrote about the idea that drugs targeting the renin–angiotensin system (RAS)—ACE inhibitors and ARBs—might have therapeutic effects beyond blood pressure, including in schizophrenia and autism. At that time, the discussion was mostly mechanistic. Today, new evidence strengthens the rationale and provides translational plausibility.

 

Why the Brain RAS Matters

While angiotensin II is best known for regulating blood pressure, the brain has its own RAS, which regulates:

·         AT₁ receptors → oxidative stress, neuroinflammation, microglial activation

·         AT₂ and Mas receptors → neuroprotection, mitochondrial function, anti-inflammatory signaling

·         ACE → converts Angiotensin I → II and degrades bradykinin, affecting cerebral blood flow

Shifting the balance from AT₁-dominated to AT₂/Mas signaling can normalize microglial function, improve neuronal energy metabolism, and support synaptic plasticity.

 

New Autism-Relevant Evidence (2025)

A recent study (Spielman et al., Molecular Psychiatry, 2025) used a mouse model of maternal anti-Caspr2 antibodies, a risk factor for some forms of autism. Male offspring showed:

·         Hyperactive microglia

·         Reduced hippocampal dendritic spines

·         Impaired social behavior

Captopril, a BBB-penetrant ACE inhibitor, reversed these deficits. In contrast, enalapril, which poorly crosses the BBB, was ineffective. Single-cell RNA sequencing revealed captopril restored microglial metabolic homeostasis (mTOR, oxidative phosphorylation, eIF2 signaling), linking microglial function directly to behavioral outcomes.

 

ACE Inhibitors vs ARBs: CNS and Immune Effects

Feature	ACE inhibitors (e.g., captopril)	ARBs (BBB-permeable, e.g., telmisartan)
↓ Ang II	Yes	No (blocks AT₁ receptor)
↑ Bradykinin / NO	Yes	No
BBB penetration	Variable — captopril high, enalapril low	Most low; telmisartan high
Microglial activation	↓ via less Ang II & more NO	↓ via AT₁ blockade
NKCC1/2 chloride cotransporters	Normalized via ↓ Ang II	Normalized via AT₁ blockade
Regulatory T cells (Tregs)	Strong ↑	Moderate ↑ (telmisartan strongest among ARBs)
Th1/Th17 autoimmunity	Modulated ↓	Modulated ↓
PPAR‑γ activation	No	Yes (telmisartan)
Evidence in ASD model	Captopril reversed phenotype (2025)	Mechanistically promising; anecdotal human benefit

Both classes modulate neuroinflammation, chloride signaling, and immune function, but ACE inhibitors and ARBs differ in mechanisms and potency.

 

Clinical Evidence in Schizophrenia

Telmisartan has been trialed in adults with schizophrenia (NCT00981526), primarily for metabolic side effects of antipsychotics (clozapine, olanzapine). Secondary observations included:

·         Improvement in negative symptoms

·         Modest cognitive benefits

·         Good tolerability over 12 weeks

This demonstrates CNS activity in humans, beyond metabolic effects, supporting translational plausibility for neuropsychiatric conditions.

 

Personal Observation in Autism

Years ago, I trialed telmisartan in my son. The effect was striking: he began singing spontaneously—something no other therapy had achieved. Singing engages emotion, motivation, and executive coordination, all dependent on healthy microglial and neuronal metabolism. While anecdotal, this observation aligns with mechanistic insights from both the mouse autism model and schizophrenia trials.

 

Safety and Accessibility

ACE inhibitors and ARBs are:

·         Widely prescribed globally for hypertension and heart protection

·         Generic, inexpensive, and safe in adults

·         Typically well-tolerated (ACE-i cough, hypotension, mild electrolyte changes)

This makes them practical candidates for drug repurposing in neurodevelopmental and neuropsychiatric disorders.

 

Mechanistic Summary

1.     Microglial hyperactivation contributes to synaptic and behavioral deficits in some autism subtypes.

2.     Brain RAS modulation (ACE-i or ARB) restores microglial homeostasis, improves energy metabolism, and supports synaptic plasticity.

3.     NKCC1/2 chloride cotransporter regulation: By reducing Ang II (ACE-i) or blocking AT₁ (ARB), these drugs normalize intracellular chloride, restoring proper GABAergic inhibition.

4.     Immune regulation: ACE inhibition induces regulatory T cells (Tregs) and modulates Th1/Th17 autoimmunity. BBB-penetrant ARBs like telmisartan also modulate these pathways, enhanced by PPAR‑γ activation.

5.     Behavioral outcomes: In mice, captopril reverses ASD-like phenotypes; anecdotal human reports suggest telmisartan may improve engagement, motivation, and communication.

 

Next Steps for Research

·         Carefully designed biomarker-driven pilot trials in humans, selecting individuals with evidence of neuroinflammation or maternal autoantibody exposure.

·         CNS-focused outcome measures (microglial imaging, inflammatory markers, synaptic function).

·         Behavioral endpoints relevant to autism (social interaction, expressive communication).

Or skip that and maybe make an n=1 trial?

 

Take-Home Message

Drugs long used for cardiovascular health may have untapped potential in neurodevelopmental and neuropsychiatric disorders. BBB-penetrant ACE inhibitors and ARBs, particularly telmisartan, can modulate:

·         Microglial activity

·         Neuronal chloride gradients

·         Immune regulation

Recent mouse data (Spielman et al., 2025) and human observations in schizophrenia support mechanistic plausibility and safety, making these drugs promising candidates for further study in selected autism subgroups.

 

References and Further Reading:

Spielman et al., Molecular Psychiatry, 2025: Captopril restores microglial homeostasis in anti-Caspr2 ASD model

NCT00981526, Telmisartan in schizophrenia (Fan X, 2018)

Lloyd-Thomas, 2017: Angiotensin II in the Brain

Lloyd-Thomas, 2017: Targeting Angiotensin in Schizophrenia and Some Autism