HomeTechBrain size could have a major impact on autism severity

Brain size could have a major impact on autism severity

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Autism can range from mild to severe (Picture: Getty/iStockphoto)

Autistic children generally fall into one of two groups – those with profound, lifelong social struggles and developmental delay, and others with milder symptoms, which often improve with time.

Now, scientists believe they have discovered what causes this significant difference.

Brain size.

A study led by the University of California San Diego has discovered that toddlers with a larger cortex – the outer layer of the brain, often called grey matter – had more severe symptoms.

Grey matter holds tens of billions of nerve cells. It is responsible for essential everyday functions including thinking, reasoning, learning, emotions and sensory functions.

Typical thinking might suggest the larger the brain, the more effective it is, but MRIs of ten toddlers between the ages of one and four revealed that the larger their brain structure, the more severe their social and language symptoms in later life.

Children with autism can display problems with learning, emotions and reasoning (Picture: Getty/Tetra)

Alongside measuring the children’s brains, the team also used stem cells to grow brain cortical organoids (BCOs) – lab-grown models of their brain in the womb. 

Hundreds of organoids were grown for each patient, and revealed that abnormal BCO growth correlated with each toddler’s disease, meaning the bigger the BCO, the more severe their symptoms.

The BCOs were also compared with those from neurotypical controls, and found to be around 40% larger.

‘The bigger the brain, the better isn’t necessarily true,’ said Dr Alysson Muotri, a director at the university’s Sanford Stem Cell Institute. ‘We found that in the brain organoids from toddlers with profound autism, there are more cells and sometimes more neurons – and that’s not always for the best.’

Brain cortical organoids (BCOs) created by Dr Alysson Muotri (Picture: UC San Diego Health Sciences)

As well as being bigger, the researchers also found that the BCOs of autistic children grew around three times faster than those of neurotypical children, in some cases even developing excess neurons.

Dr Eric Courchesne, a professor in the School of Medicine’s Department of Neurosciences, said: ‘The core symptoms of autism are social affective and communication problems. We need to understand the underlying neurobiological causes of those challenges and when they begin. We are the first to design an autism stem cell study of this specific and central question.’

Autism is a complex disorder, with no single cause. However, scientists have long noted two distinct categories, without knowing why some have severe struggles and require lifelong care, while others have a much milder condition, often going on to develop good language skills and social relationships.

The new research has shown that changes to the brain begin in the womb, and the team hopes it will one day help identify the cause, raising the possibility of a therapy to one day ease symptoms.

The study is published in the journal Molecular Autism.


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