Understanding how and why regression occurs in young children with either polygenic or single gene autism

 

Just ask Peter

I see that in the US, RFK Jr has told the President that he will figure out the cause of the autism epidemic by September 2025. Well, some people are saying that will be impossible. The facts are actually already there in the research, if you care to look for them. It might have been better to give the task to Elon Musk and give him 6 days, rather than RFK 6 months.

Today, I thought it would be interesting to address the issue of how apparently typically developing young toddlers can regress into autism. This post was written at Musk++ speed.

 

What is autism?

Autism is a complex neurodevelopmental condition that can manifest in diverse ways. One particularly perplexing phenomenon is regression—the loss of previously acquired skills such as speech, social interaction, or motor abilities. Regression typically occurs between 18 months and 5 years of age and can be observed in both polygenic (several genes affected) and monogenic (single gene) forms of autism. Understanding why and how this occurs requires examining the interplay between genetic, metabolic, and environmental factors during critical periods of early brain development.

 

Key Processes in Early Brain Development

Synaptic Pruning and Plasticity

During early childhood, the brain refines its neural connections through a process known as synaptic pruning, where unused or weaker synapses are eliminated, and stronger ones are reinforced. This process is essential for optimizing neural circuits but is highly vulnerable to dysregulation. In conditions like Rett syndrome, caused by mutations in the MECP2 gene, or in polygenic autism, excessive or insufficient pruning can disrupt circuits necessary for maintaining skills. 

Myelination

Myelination—the coating of axons with myelin to improve signal transmission—occurs rapidly during this period. Disruptions in myelination due to metabolic dysfunctions or mitochondrial impairments can impair communication between brain regions, potentially contributing to skill regression. 

Critical Periods of Neuroplasticity

Early childhood represents a window of heightened neuroplasticity, where the brain’s capacity to adapt and rewire is greatest. This sensitivity allows for rapid learning but also renders the brain more susceptible to adverse influences, such as inflammation, energy deficits, or genetic mutations. Dysregulation of plasticity mechanisms can lead to maladaptive changes, erasing previously acquired skills. 

Mitochondrial Dysfunction: A Key Factor

Mitochondrial dysfunction has been increasingly implicated in autism regression. The brain’s energy demands are extraordinarily high during early childhood, consuming up to 50% of the body’s total energy to support growth and neural connectivity. Mitochondrial deficits, whether due to genetic mutations or environmental stressors, can cause energy crises that disrupt critical developmental processes. Dr. Richard Kelley from Johns Hopkins has highlighted mitochondrial dysfunction as a near-universal factor in cases of regression.

Kelley proposed the diagnosis AMD, autism secondary to mitochondrial disease.

Evaluation and Treatment of Patients with Autism and Mitochondrial Disease 

Unfortunately, there are many factors other than mitochondrial dysfunction that cause regression into autism. This point has been highlighted by many readers of this blog, based on their own experiences.

 

Age-Specific Vulnerability

 

Why Regression Occurs Between 18 Months and 5 Years

This period is marked by rapid acquisition of key developmental milestones, including speech, language, and social skills. These abilities rely on the integrity of neural circuits that are still maturing. Regression is more apparent when these nascent circuits are disrupted, as the skills they support are not yet deeply embedded.

• Before 18 Months: Skills like speech or social interaction are not fully developed, making regression less visible.
• After 5 Years: Neural circuits and skills stabilize, and the brain becomes less susceptible to environmental and metabolic disruptions.

 

The Role of Synaptic and Circuit Stability

Regression is less likely in older children or adults because the brain has completed most of its synaptic pruning and has established more stable circuits. By this time, skills are less reliant on vulnerable developmental processes.

 

Environmental and Epigenetic Triggers

During early childhood, environmental factors such as infections, stress, or dietary deficiencies can significantly influence gene expression and neurodevelopment. In genetically predisposed children, these triggers can lead to neuroinflammation or exacerbate mitochondrial dysfunction, further increasing the risk of regression.

 

Polygenic vs. Monogenic Autism Regression

• Monogenic Autism: In single-gene disorders like Rett syndrome or Fragile X syndrome, genetic mutations directly impair brain development and function. Regression in these cases is often linked to disruptions in genes crucial for synaptic maintenance and neuroplasticity.

• Polygenic Autism: Regression in polygenic autism likely results from a combination of genetic predispositions interacting with environmental and metabolic stressors. The cumulative effect of multiple risk genes can dysregulate processes like synaptic pruning, energy metabolism, or immune responses.

 

Regression up the age of 10 is rare, but possible

Childhood Disintegrative Disorder (CDD), also known as Heller's syndrome, is a rare condition characterized by significant regression in developmental skills after at least two years of apparently typical development. It is classified as a part of the autism spectrum disorders,  but is distinct due to its dramatic loss of previously acquired skills, typically between the ages of 3 and 10 years.

CDD is often considered a more severe form of regressive autism because of the profound and widespread nature of the regression:

• Loss of language, social skills, motor skills, and adaptive behaviors (e.g., toileting).
• Behavioral changes often include anxiety, irritability, and stereotypic behaviors resembling autism.

However, its exact cause remains poorly understood, with current hypotheses focusing on both polygenic inheritance and mitochondrial dysfunction.

CDD is a spectrum with a wide range of outcomes. While it is often associated with severe and permanent disability, some children can regain partial skills with appropriate interventions. Recovery varies greatly, and prognosis depends on factors such as the timing and extent of regression, the underlying cause, and the availability of tailored therapeutic approaches.

Simple conclusion

Regression in autism is a multifaceted phenomenon that occurs during a critical window of early childhood when the brain is rapidly developing and highly sensitive to disruption. Key processes such as synaptic pruning, myelination, and neuroplasticity are particularly vulnerable to genetic, metabolic, and environmental influences. Mitochondrial dysfunction emerges as a central factor in many cases, highlighting the need for a deeper understanding of energy metabolism in neurodevelopmental disorders. While the mechanisms differ between polygenic and monogenic autism, both forms underscore the importance of this critical developmental window and the need for timely interventions to support skill retention and neurodevelopment.

 

How Mitochondrial Dysfunction Causes Regression

1. Energy Crisis in the Brain
• The brain is highly energy-dependent, consuming a significant portion of the body’s ATP (adenosine triphosphate), produced by mitochondria.
• Skills like speech and motor function rely on the continuous and efficient operation of neural networks. If mitochondria cannot meet the energy demands, these networks may fail to maintain function, leading to regression.
2. Critical Periods of High Energy Demand
• Developmental regression often occurs during phases of rapid brain growth and synaptic pruning (e.g., 18 months to 3 years in children with autism).
• During these periods, mitochondrial dysfunction can result in:
• Depletion of neural energy reserves
• Impaired synaptic plasticity and signaling
• Loss of functional neural networks
3. Vulnerability to Stressors
• Children with mitochondrial dysfunction are more susceptible to stressors such as infections, fevers, or environmental toxins, which can further impair mitochondrial function and precipitate regression.
4. Oxidative Stress and Neuroinflammation
• Dysfunctional mitochondria generate excessive reactive oxygen species (ROS), leading to oxidative stress and damage to cellular components, including neurons.
• This can exacerbate inflammation in the brain and contribute to neural circuit disruptions.

 

Example of single gene autisms featuring regression 

Rett Syndrome Overview

• Rett syndrome is caused by mutations in the MECP2 gene, which encodes the methyl-CpG-binding protein 2. This protein is critical for regulating gene expression, particularly in neurons.
• MECP2 acts as a transcriptional regulator, ensuring that certain genes are activated or repressed as needed during development.

Why Development Seems Normal Initially

1. Early Brain Development
• During early development, processes like neuronal proliferation (growth in the number of neurons) and initial migration of neurons to their proper locations occur.
• These stages of brain development are not as heavily dependent on MECP2 function, which primarily regulates post-mitotic (non-dividing) neurons.
• Other compensatory mechanisms in early life might temporarily mask the effects of MECP2 dysfunction.
2. Low Demand for Synaptic Plasticity
• In the first year of life, the brain focuses on basic structural growth rather than complex synaptic connections.
• The regulatory role of MECP2 in maintaining synaptic plasticity becomes more critical as the child begins to acquire higher cognitive and motor functions.

 

Why Regression Occurs

1. Synaptic Maturation and Plasticity
• Around 18 months, the brain enters a critical phase of synaptic pruning and circuit refinement, where unnecessary connections are removed, and essential ones are strengthened.
• MECP2 dysfunction leads to impaired synaptic maturation, resulting in disrupted communication between neurons.
• This manifests as the loss of previously acquired skills, such as speech, purposeful hand use, and motor coordination.
2. Epigenetic Dysregulation
• MECP2 is a key player in epigenetic regulation, meaning it modifies how genes are expressed without changing the DNA sequence.
• During this developmental window, MECP2 is critical for the fine-tuning of neural circuits through epigenetic mechanisms. A defective MECP2 protein disrupts these processes, leading to neurodevelopmental regression.
3. Imbalance in Excitation and Inhibition
• MECP2 mutations often result in an imbalance between excitatory and inhibitory signaling in the brain, leading to abnormal neural activity patterns.
• This imbalance might not become evident until the neural network demands increase during the toddler years.

 

Why the Timing?

• Critical Periods: Brain development occurs in stages with "critical periods" where specific genes and proteins are essential. MECP2 dysfunction becomes evident when the brain transitions from basic growth to complex functional organization.
• Developmental Threshold: The early compensatory mechanisms or residual MECP2 activity may be sufficient for initial growth but fail as demands on the neural system intensify.

 

Implications for Treatment

• Early Interventions: Therapies like MECP2 gene therapy, neuroplasticity-enhancing interventions, and symptom management strategies aim to prevent or reduce the impact of regression.
• Critical Timing: Intervening before or during the regression window may maximize the potential for preserving neural function.

This pattern of normal early development followed by regression highlights the dynamic and stage-specific roles that single-gene mutations can play in neurodevelopment.

  

Contrast Pitt-Hopkins syndrome vs Rett syndrome

Pitt-Hopkins syndrome and Rett syndrome are both monogenic disorders associated with autism-like features, but they differ significantly in their developmental trajectories and underlying mechanisms.

Newborns with Pitt-Hopkins syndrome often appear physically normal, with no distinct features at birth to suggest a genetic syndrome. Birth weight and head circumference may fall within normal ranges. Developmental delays, especially in motor skills, usually become noticeable during the first year of life. Hypotonia (low muscle tone) may be evident early, affecting feeding and physical development. Pitt-Hopkins syndrome typically does not feature a dramatic loss of previously acquired skills (regression) as seen in conditions like Rett syndrome. Instead, Pitt-Hopkins is more characterized by delayed acquisition of developmental milestones rather than a significant loss of skills once they are gained.

 

Pitt-Hopkins Syndrome (TCF4 Mutation)

• Developmental Course: Children with Pitt-Hopkins syndrome typically show early developmental delays, particularly in motor and cognitive domains. While there may be some regression, it is less abrupt and pronounced compared to Rett syndrome.
• Mechanism: Mutations in the TCF4 gene disrupt transcriptional regulation critical for neuronal differentiation and synaptic formation. This leads to global developmental delays from early infancy, with limitations in skill acquisition rather than significant loss of previously acquired abilities.
• Features: Severe intellectual disability, absent or minimal speech, and distinctive facial features are characteristic. Respiratory irregularities and motor impairments are common.

Rett Syndrome (MECP2 Mutation)

• Developmental Course: Girls with Rett syndrome often develop typically for the first 6 to 18 months before experiencing a dramatic regression. Skills such as speech, purposeful hand use, and social engagement are lost, often accompanied by the onset of stereotypic hand movements.
• Mechanism: MECP2 mutations impair the regulation of gene expression involved in synaptic maintenance and neuroplasticity. This results in the progressive loss of neuronal function and connectivity, particularly during the sensitive period of early childhood.
• Features: Rett syndrome includes severe intellectual disability, motor impairments, seizures, and breathing abnormalities, along with hallmark hand-wringing behaviors.

 

Polygenic regressive autism

In polygenic regressive autism, the regression is believed to result from a complex interplay of multiple genetic, environmental, and metabolic factors. Unlike monogenic autism, where a single gene mutation explains most of the phenotype (e.g., Rett syndrome), polygenic regressive autism arises from the combined effects of multiple genetic variants, each contributing a small risk, along with external triggers

 

1. Key Features of Regression in Polygenic Autism

• Loss of previously acquired skills (e.g., speech, social interaction, motor abilities) after a period of typical development.
• Often occurs between 18 and 36 months, a critical period for brain development.
• Associated with a subset of autism cases, possibly more linked to environmental sensitivity or metabolic vulnerabilities.

 

2. Contributing Factors

 

Genetic Susceptibility

• Multiple Genes Involved: Variants in genes related to synaptic function, neural plasticity, and energy metabolism (e.g., SHANK3, SLC6A4, SCN2A) may predispose the brain to functional impairments.
• Epistasis: Interactions between these genes amplify the risk of neural circuit disruptions.

Epistasis is a Greek word for stoppage and in science when you want to sound clever, you often pick a Greek word, so only Greeks will understand it.

Our Greek reader Konstantinos is currently dealing with the implications of epistasis.

Epistasis is a precise term used in genetics. It refers to specific interactions between genes where one gene modifies, suppresses, or enhances the effect of another gene. This is a technical concept that has well-defined implications in studies of inheritance and molecular biology. For example:

• Gene A masks the effect of Gene B.

• Gene C enhances the effect of Gene D.

Mitochondrial Dysfunction

• Energy Deficits: The developing brain has high energy demands, especially during synaptic pruning and circuit refinement. If mitochondria are inefficient, neural circuits may fail.
• Triggered by Stress: Stressors like fever, infections, or environmental toxins may overwhelm already fragile mitochondrial function, causing regression.

Excitatory-Inhibitory Imbalance

• Synaptic Dysregulation: Variants in genes affecting GABAergic (inhibitory) or glutamatergic (excitatory) signaling can lead to circuit over or under-activation, resulting in regression.
• Neuroinflammation: Chronic inflammation may exacerbate synaptic dysfunction, further disrupting brain networks.

Immune and Neuroinflammatory Factors

• Maternal Immune Activation (MIA): In utero exposure to maternal immune challenges may predispose the child to neuroinflammation, which could be triggered later in life.
• Postnatal Immune Dysregulation: Autoimmune or inflammatory responses (e.g., microglial activation) may interfere with neural connectivity.

Epigenetic and Environmental Triggers

• Epigenetic Modifications: Environmental factors, such as nutrition, infections, or toxins, can influence the expression of autism-related genes.
• Gut-Brain Axis: Dysbiosis or gut inflammation may exacerbate systemic inflammation, impacting brain function.

 

3. What Happens Neurologically?

Synaptic Dysfunction

• Dendritic Spine Abnormalities: Regression is often associated with a loss of dendritic spines, impairing synaptic connections.
• Neuronal Circuitry Breakdown: Brain regions critical for speech, social cognition, and motor skills may lose functional connectivity.

Myelination and Axonal Integrity

• While widespread demyelination is not typical, localized impairments in white matter connectivity may slow information processing in key circuits.

Neuronal Stress and Oxidative Damage

• Reactive Oxygen Species (ROS): Mitochondrial inefficiency leads to oxidative stress, damaging neurons and synapses.
• Excitotoxicity: Overactivation of neurons due to excitatory-inhibitory imbalances can lead to synaptic burnout.

Neuroinflammation

• Microglial Activation: Overactive microglia can prune healthy synapses, leading to regression.
• Cytokine Dysregulation: Elevated inflammatory markers (e.g., IL-6, TNF-alpha) are frequently observed in regressive autism.

4.   Why Are Skills Lost?

• Functional Overload: Circuits supporting skills like speech or motor coordination are highly energy-dependent. Mitochondrial dysfunction or inflammation can make these circuits fail under stress.
• Synaptic Pruning: Abnormal or excessive pruning during development can eliminate neural pathways necessary for previously learned skills.
• Metabolic Crisis: Temporary or chronic deficits in energy production impair the maintenance of neural plasticity required for skill retention.

 

5. Potential Triggers for Regression

• Fever or Infections: Increase metabolic demand and inflammatory markers, overwhelming the child's already vulnerable systems.
• Vaccines or Illnesses: Vaccines do not directly cause autism, but in rare cases of mitochondrial dysfunction, the immune activation they trigger may become excessive and act as a major stressor and cause a "power outage." Regressive autism is the consequence.
• Environmental Toxins: Pesticides, heavy metals, and air pollution can exacerbate oxidative stress and mitochondrial inefficiency.
• Nutritional Deficits: Inadequate intake of key nutrients (eg CoQ10, carnitine, B vitamins) may worsen mitochondrial dysfunction.

 

What about early-onset polygenic autism (the main type)?

Well, this post was to explain regressive autism.

Nonetheless, here is the difference between early-onset polygenic autism and regressive polygenic autism.

The specific genetic makeup in polygenic autism likely plays a critical role in determining whether autism manifests as early-onset or regressive autism. The timing and nature of symptoms can depend on the functions of the genes involved, their interactions, and the biological systems they affect.

Early-Onset Autism

• Key Features:

• Symptoms are evident from infancy.
• Includes difficulties with social engagement, communication, and restricted interests or repetitive behaviors from an early age.

• Genetic Contributions:

• Synaptic genes: Mutations or variations in genes like SHANK3, SYNGAP1, and NRXN1 disrupt synaptic formation and function during early brain development. This can lead to abnormalities in the foundational wiring of the brain, manifesting as early-onset autism.
• Genes affecting neurodevelopment: Genes regulating early neuronal proliferation, migration, or differentiation may predispose to early structural or functional deficits.
• Reduced redundancy: Early-onset cases might involve high-impact mutations in critical pathways, such as those regulating synaptic plasticity, which leave little compensatory capacity for normal development.
•  

Regressive Autism

• Key Features:

• Normal or near-normal development during infancy.
• Loss of previously acquired skills, typically occurring between 18 months and 5 years of age.

• Genetic Contributions:

• Mitochondrial dysfunction-related genes: Variants in genes involved in mitochondrial energy metabolism (e.g. NDUFS4, SLC25A12) may impair the brain's ability to meet energy demands during rapid synaptic pruning and development, triggering regression.
• Immune or inflammatory response genes: Variations in genes affecting immune regulation (e.g. HLA genes, cytokine signaling genes) could result in neuroinflammation during critical developmental windows, leading to regression.
• Activity-dependent plasticity genes: Genes like MEF2C or UBE3A are involved in maintaining synaptic connections based on neuronal activity. Disruptions could lead to the loss of skills as synaptic pruning occurs.
• Environmental sensitivity: Some polygenic profiles might predispose individuals to environmental triggers (e.g. infections, stress, or dietary changes), unmasking vulnerabilities during critical developmental phases.

 

Gene combinations and their timing effects

• The interaction of multiple genes likely determines whether autism manifests as early-onset or regressive:

• High-impact mutations in multiple pathways (e.g. synaptic formation and plasticity) might produce early-onset autism.
• Combinations of moderate-risk variants that interact with environmental or biological stressors (e.g., immune challenges or mitochondrial stress) may predispose to regression.
• Timing of gene expression: Genes active during infancy might contribute to early-onset autism, while those playing roles during later synaptic refinement may contribute to regression.

 

Polygenic Disorders that Overlap – Autism(s), Schizophrenia(s), Bipolar(s) and ADHD(s) – Creativity & Intelligence

Blogs are inevitably rather jumbled up and lack a clear structure; today’s post really should be at the beginning.

One clear message from the more sophisticated research into neuropsychiatric disorders is that they are generally associated with variances in the expression of numerous different genes, making them polygenic.

What I find interesting is that there is a substantial overlap in the genes that are miss-expressed across different neuropsychiatric disorders.  This is further proof, if it was needed, that the observational diagnoses used by psychiatrists are rather primitive.

So individual people will have a near unique set of genetic variances that make their symptoms slightly different to everyone else.  However it is highly likely that discrete biological dysfunctions will exist across the diagnoses.  So for example elevated intracellular chloride will be found in some autism and some schizophrenia. A calcium channelopathy affecting Cav1.2 would be found in some autism and some bipolar.

Eventually you would dispose of the old observational diagnoses like bipolar and give the biological diagnoses.  Then you will have the same drugs being used in a person with “bipolar” and another with “autism”.  When all this will happen is no time soon. 

In the meantime people interested in autism can benefit from the research into the other neuropsychiatric disorders.  These other disorders can be much better researched, partly because they usually concern adults who are fully verbal and have typical IQ.  In many cases there are both hypo and hyper cases in these disorders.   

Also of interest is that the same unusual gene expression in schizophrenia/bipolar is linked to creativity and the autism genes to intelligence. This is put forward as an explanation as to why evolution has conserved rather than erased neuropsychiatric disorders.

Height is polygenic 

Let’s start will a simple example.

There is no single gene that determines your height. Some school books suggest 3 or 4 genes, so let’s assume that is correct for now.

Traits are polygenic when there is wide variation. For example, humans can be many different sizes. Height is a polygenic trait, controlled by at least three genes with six alleles. If you are dominant for all of the alleles for height, then you will be very tall. There is also a wide range of skin colour across people. Skin colour is also a polygenic trait, as are hair and eye colour.

Polygenic inheritance often results in a bell shaped curve when you analyze the population. Most people fall in the middle of the phenotypic range, such as average height, while very few people are at the extremes, such as very tall or very short. At one end of the curve will be individuals who are recessive for all the alleles (for example, aabbcc); at the other end will be individuals who are dominant for all the alleles (for example, AABBCC). Through the middle of the curve will be individuals who have a combination of dominant and recessive alleles (for example, AaBbCc or AaBBcc).

There may be 4 or 6 or more alleles involved in the phenotype. At the left extreme, individuals are completely dominant for all alleles, and at the right extreme, individuals are completely recessive for all alleles. Individuals in the middle have various combinations of recessive and dominant alleles.

Unfortunately the real world is a bit more complex than high school biology. 

Defining the role of common variation in the genomic and biological architecture of adult human height

“Our results indicate a genetic architecture for human height that is characterized by a very large but finite number (thousands) of causal variants.”

Genes vs the Environment 

The spectrum of human diseases are caused by a multitude of genetic and environmental factors acting together. In certain conditions such as Down syndrome , genetic factors predominate, while in infections for example, environmental factors predominate. Most chronic non-communicable conditions such as schizophrenia and diabetes as well as congenital malformations are caused by an interaction of both genetic and environmental factors.

Source: http://www.gfmer.ch/SRH-Course-2010/course-files/pdf/Multifactorial-polygenic-inheritance-Hamamy-2010.pdf

The environment and epigenetic change

Some environmental influences, like smoking or pollution, can also become genetic in that heritable epigenetic markers can become tagged to a specific gene.  This impacts whether it is turned on or off.  

Multifactorial vs Polygenic Inheritance 

Multifactorial inheritance diseases that show familial clustering but do not conform to any recognized pattern of single gene inheritance are termed multifactorial disorders. They are determined by the additive effects of many genes at different loci together with the effect of environmental factors.

These conditions show a definite familial tendency but the incidence in close relatives of affected individuals is usually around 2-4%, instead of the much higher figures that would be seen if these conditions were caused by mutations in single genes (25-50%).

Examples of disorders of multifactorial inheritance

·        asthma

·        schizophrenia

·        diabetes mellitus

·        hypertension

Polygenic inheritance involves the inheritance and expression of a phenotype being determined by many genes at different loci, with each gene exerting a small additive effect. Additive implies that the effects of the genes are cumulative, i.e. no one gene is dominant or recessive to another.

According to the liability/threshold model, all of the factors which influence the development of a multifactorial disorder, whether genetic or environmental, can be considered as a single entity known as liability.

The liabilities of all individuals in a population form a continuous variable, which can be exemplified by a bell shaped curve.

Individuals on the right side of the threshold line represent those affected by the disorder. 

In autism the threshold keeps being moved, because the definition of the disease keeps being widened.

Liability curves of affected and their relatives

The liability curve is relevant to the question posed by parents who have autism in the family and want to know whether it will occur again and also to grown up siblings of those with autism.

The curve for relatives of affected will be shifted to the right; so the familial incidence is higher than the general population incidence.

So the biggest future autism risk is likely to be a previous occurance. 

There are ways to actively promote protective factors and shift the curve back to the left; but a risk will remain. 

Evidence that Autism is Polygenic 

This is a paper from 2016 that looks at how the genetic risks are additive.

Polygenic transmission disequilibrium confirms that common and rare variation act additively to create risk for autism spectrum disorders 

Autism spectrum disorder (ASD) risk is influenced by both common polygenic and de novo variation. The purpose of this analysis was to clarify the influence of common polygenic risk for ASDs and to identify subgroups of cases, including those with strong acting de novo variants, in which different types of polygenic risk are relevant. To do so, we extend the transmission disequilibrium approach to encompass polygenic risk scores, and introduce with polygenic transmission disequilibrium test. Using data from more than 6,400 children with ASDs and 15,000 of their family members, we show that polygenic risk for ASDs, schizophrenia, and educational attainment is over transmitted to children with ASDs in two independent samples, but not to their unaffected siblings. These findings hold independent of proband IQ. We find that common polygenic variation contributes additively to ASD risk in cases that carry a very strong acting de novo variant. Lastly, we find evidence that elements of polygenic risk are independent and differ in their relationship with proband phenotype. These results confirm that ASDs' genetic influences are highly additive and suggest that they create risk through at least partially distinct etiologic pathways.

  

The Genetics of Autism: Key Issues, Recent Findings and Clinical Implications

Summary and Conclusions

Autism and related conditions are highly heritable disorders. Consequently, gene discovery promises to help elucidate the underlying pathophysiology of these syndromes and, it is hoped, eventually improve diagnosis, treatment, and prognosis. The genetic architecture of autism is not yet known. What can be said from the studies to date is that writ large, autism is not a monogenic disorder with Mendelian inheritance. In many, but clearly not all individual cases, it is likely to be a complex genetic disorder that results from simultaneous genetic variations in multiple genes. The CDCV hypothesis predicts that the risk alleles in Autism and other complex disorders will be common in the population. However, recent evidence both with regard to autism and other complex disorders, raises significant questions regarding the overall applicability of the theory and the extent of its usefulness in explaining individual genetic liability. In addition, considerable evidence points to the importance of rare alleles for the overall population of affected individuals as well as their role in providing a foothold into the molecular mechanisms of disease. Finally, there is debate regarding the clinical implications of autism genetic research to date. Most institutional guidelines recommend genetic testing or referral only for idiopathic autism if intellectual disability and dysmorphic features are present. However, recent advances suggest that the combination of several routine tests combined with a low threshold for referral is well-justified in cases of idiopathic autism.

So What is Autism? 

Most people’s autism is of unknown cause (idiopathic) and this is most likely to be polygenic, but highly likely to have some environmental influences making it multifactorial.

What is interesting and potentially relevant to therapy is that the polygenic footprint of autism overlaps with those causing other neuropsychiatric diseases like bipolar, schizophrenia and even ADHD.

As you broaden the definition of autism and so move the threshold you will eventually diagnose everyone as having autism; because we all have some autism genes.

Autism genes are in all of us, new research reveals

This does then start to be ridiculous, but in some ways we are now at the point where quirky but normal has become quirky autistic.

This same questionable position of where to draw the threshold applies to all such disorders (bipolar, ADHD etc.).  At what point does a difference become a disorder?

Where things currently stand more than 10% of the population have an autism-gene-overlapping diagnosis.  That is a lot and suggests that things are getting a little out of control.  Perhaps better to raise the threshold for where difference become disorder?

 Percent of the population affected by various disorders genetically overlapping to strictly define autism (SDA). Estimates of prevalence vary widely by country and study.

If you raise the threshold for how severe autism has to be, you soon lose the quirky autism. A stricter approach to diagnosing ADHD would mean losing the people that will naturally “grow out of it” and leave a much smaller group that might genuinely benefit from medical intervention. We saw in an earlier post that the percentage of kids with ADHD given drugs varies massively among developed countries, with the US at the top and France at the bottom. Here is another article on this subject.

Why French Kids Don't Have ADHD

Autism overlapping with Schizophrenia, Bipolar ADHD etc.

There are now numerous different studies showing how the large number of genes that underlie each observational diagnosis overlap with each other.

Shared molecular neuropathology across major psychiatric disorders parallels polygenic overlap

One Sentence Summary: Autism, schizophrenia, and bipolar disorder share global gene expression patterns, characterized by astrocyte activation and disrupted synaptic processes.

Recent large-scale studies have identified multiple genetic risk factors for mental illness and indicate a complex, polygenic, and pleiotropic genetic architecture for neuropsychiatric disease. However, little is known about how genetic variants yield brain dysfunction or pathology. We use transcriptomic profiling as an unbiased, quantitative readout of molecular phenotypes across 5 major psychiatric disorders, including autism (ASD), schizophrenia (SCZ), bipolar disorder (BD), depression (MDD), and alcoholism (AAD), compared with carefully matched controls. We identify a clear pattern of shared and distinct gene-expression perturbations across these conditions, identifying neuronal gene co-expression modules downregulated across ASD, SCZ, and BD, and astrocyte related modules most prominently upregulated in ASD and SCZ. Remarkably, the degree of sharing of transcriptional dysregulation was strongly related to polygenic (SNP-based) overlap across disorders, indicating a significant genetic component. These findings provide a systems-level view of the neurobiological architecture of major neuropsychiatric illness and demonstrate pathways of molecular convergence and specificity.

We observe a gradient of synaptic gene down-regulation, with ASD > SZ > BD. BD and SCZ appear most similar in terms of synaptic dysfunction and astroglial activation and are most differentiated by subtle downregulation in microglial and endothelial modules. ASD shows the most pronounced upregulation of a microglia signature, which is minimal in SCZ or BD. Based on these data, we hypothesize that a more severe synaptic phenotype, as well as the presence of microglial activation, is responsible for the earlier onset of symptoms in ASD, compared with the other disorders, consistent with an emerging understanding of the critical non-inflammatory role for microglia in regulation of synaptic connectivity during neurodevelopment (39, 66). MDD shows neither the synaptic nor astroglial pathology observed in SCZ, BD. In contrast, in MDD, a striking dysregulation of HPA-axis and hormonal signalling not seen in the other disorders is observed. These results provide the first systematic, transcriptomic framework for understanding the pathophysiology of neuropsychiatric disease, placing disorder-related alterations in gene expression in the context of shared and distinct genetic effects.

  

Common polygenic variation contributes to risk of schizophrenia that overlaps with bipolar disorder

Schizophrenia risk genes tied to immunity, autism

Several of the variants lie in regions important for immune function and associated with autism. This suggests that both disorders stem partly from abnormal activation of the immune system, say some researchers.

Brain tissue study bolsters autism, schizophrenia link

The study builds on previous work, in which Arking’s team characterized gene expression in postmortem brain tissue from 32 individuals with autism and 40 controls². In the new analysis, the researchers made use of that dataset as well as one from the Stanley Medical Research Institute that looked at 31 people with schizophrenia, 25 with bipolar disorder and 26 controls³.

They found 106 genes expressed at lower levels in autism and schizophrenia brains than in controls. These genes are involved in the development of neurons, especially the formation of the long projections that carry nerve signals and the development of the junctions, or synapses, between one cell and the next. The results are consistent with those from previous studies indicating a role for genes involved in brain development in both conditions.

“On the one hand, it’s exciting because it tells us that there’s a lot of overlap,” says Jeremy Willsey, assistant professor of psychiatry at the University of California, San Francisco, who was not involved in the work. “On the other hand, these are fairly general things that are overlapping.”

Full paper

Transcriptome analysis of cortical tissue reveals shared sets of downregulated genes in autism and schizophrenia

Schizophrenia/Bipolar linked to Creativity? Autism linked to Intelligence?

Since we see that neuropsychiatric disorders are substantially polygenic, the question arises why they have been evolutionarily conserved. Over thousands of years why have these traits not just faded away?

That question was raised, and answered again, in a recent autism study at Yale.  The same wide cluster of genes that may lead trigger autism are again seen to be linked to higher intelligence. You may get autism, higher intelligence, both or indeed neither, but people with those genes have a higher likelihood of autism and/or a higher IQ.

Previous studies have linked bipolar/schizophrenia to creativity, so you would expect artists and stage actors to have a higher incidence of those disorders.

In terms of evolutionary selection, clearly creativity and intelligence have been valued and so the associated disorders did not fade away over thousands of years.
  

Genetic risk of autism spectrum disorder linked to evolutionary brain benefit

“It might be difficult to imagine why the large number of gene variants that together give rise to traits like ASD are retained in human populations — why aren’t they just eliminated by evolution?” said Joel Gelernter, the Foundations Fund Professor of Psychiatry, professor of genetics and of neuroscience, and co-author. “The idea is that during evolution these variants that have positive effects on cognitive function were selected, but at a cost — in this case an increased risk of autism spectrum disorders.” 

Schizophrenia, bipolar disorder may share genetic roots with creativity

Common polygenic risk for autism spectrum disorder (ASD) is associated with cognitive ability in the general population.

Abstract

Cognitive impairment is common among individuals diagnosed with autism spectrum disorder (ASD) and attention-deficit hyperactivity disorder (ADHD). It has been suggested that some aspects of intelligence are preserved or even superior in people with ASD compared with controls, but consistent evidence is lacking. Few studies have examined the genetic overlap between cognitive ability and ASD/ADHD. The aim of this study was to examine the polygenic overlap between ASD/ADHD and cognitive ability in individuals from the general population. Polygenic risk for ADHD and ASD was calculated from genome-wide association studies of ASD and ADHD conducted by the Psychiatric Genetics Consortium. Risk scores were created in three independent cohorts: Generation Scotland Scottish Family Health Study (GS:SFHS) (n=9863), the Lothian Birth Cohorts 1936 and 1921 (n=1522), and the Brisbane Adolescent Twin Sample (BATS) (n=921). We report that polygenic risk for ASD is positively correlated with general cognitive ability (beta=0.07, P=6 × 10(-7), r(2)=0.003), logical memory and verbal intelligence in GS:SFHS. This was replicated in BATS as a positive association with full-scale intelligent quotient (IQ) (beta=0.07, P=0.03, r(2)=0.005). We did not find consistent evidence that polygenic risk for ADHD was associated with cognitive function; however, a negative correlation with IQ at age 11 years (beta=-0.08, Z=-3.3, P=0.001) was observed in the Lothian Birth Cohorts. These findings are in individuals from the general population, suggesting that the relationship between genetic risk for ASD and intelligence is partly independent of clinical state. These data suggest that common genetic variation relevant for ASD influences general cognitive ability.

  

Conclusion

Given the overlap between so many neuropsychiatric disorders it might be helpful if psychiatrists were more aware of the limitations of their observational diagnoses.

There is no singular schizophrenia like there is no single autism. They are all intertwined.  A mood disturbance in Asperger’s may have plenty in common with one in schizophrenia and respond to the same therapy.  Not surprisingly an off-label treatment in autism may work wonders for someone who is bipolar.

Probably the tighter you define autism the more there will be biological overlaps with bipolar/schizophrenia.

While there are overlaps there are other areas where autism is the opposite of bipolar and/or schizophrenia.

From a therapeutic perspective, since schizophrenia therapies have been more deeply researched than those of autism, it is always well work checking schizophrenia research for evidence.

The multifactorial approach does help explain the increasing incidence of more severe autism as environmental insults increase in modern life and we accumulate epigenetic damage.  The studies linked autism/schizophrenia with immunity genes and there is has been a continuing rise in other auto-immune, disease like asthma.

The ever sliding diagnosis threshold substantially explains much of the great increase in mild autism.

You can also use this framework to work out how to reduce the incidence of autism in future generations, but it seems that human nature continues to work in the opposite way.

Partner preferences may contribute to autism prevalence

Environmental factors are simple to modify, reducing risk factors and increasing protective factors.

If you think like Knut Wittkowski you might look at the tail of autism liability curve and try to identify those future people. Those people are likely to have some of the 700 autism risk genes over/under expressed and might benefit from some preventative therapy to minimize the coming developmental damage.  Knut thinks that Mefanemic acid will do the job. There are numerous other ideas.