In a nutshell: Brain-mapping studies of a syndrome that increases the risk of developing schizophrenia can help researchers to understand the brain changes leading to the emergence of this psychiatric disorder.

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Normally, we have two copies of each gene in our DNA: one from our mother and one from our father. However, copy number variation – a natural process in which large segments of our DNA is duplicated or deleted – can alter the number of copies of each gene. Although these variations help to make us all different from one another, they can also lead to developmental disorders and disease.

The most common copy number variant in humans is 22q11.2 – a short deletion near the middle of chromosome 22. In addition to being associated with birth defects and learning disabilities, 22q11.2 deletion syndrome (22q11.2DS) is linked to neurodevelopmental brain disorders such as schizophrenia, autism and attention deficit hyperactivity disorder.

In the past decade, advances in electroencephalography (EEG) and magnetic resonance imaging (MRI) have enabled researchers to map the brain in detail, linking changes in the structure or organisation of brain cells to human behaviour. Many research groups have looked specifically at the brains of people with 22q11.2DS.

To understand what this field of research has achieved – and what questions remain – Brain Function CoE researchers Melissa Larsen, Ilvana Dzafic and Marta Garrido from the University of Queensland and their colleague from the University of Copenhagen reviewed studies on changes in the brains of people with 22q11.2DS.

In particular, the researchers focused on studies investigating parts of the brain involved in sensory processing, working memory, response inhibition and social behaviour – all of which can be impaired in people with schizophrenia. Studies show that in most cases, the same impairments appear in people with 22q11.2DS and people with schizophrenia.

The researchers noted that the relatively small number of individuals with 22q11.2DS – which affects fewer than 1 person in 4000 – is a drawback in brain imaging studies and could be one reason why some studies have conflicting results. Studies on human health and behaviour are more robust and reliable if they include a large number of participants – otherwise it can be difficult to tell whether the relationship between two things (such as brain structure and behaviour) is meaningful or has happened by chance.

At the end of their review, the researchers emphasize that more studies looking at a larger number of people are needed to provide a stronger link between the brain changes involved in 22q11.2DS and those linked to schizophrenia. Understanding more about these brain changes could help to explain how brain disorders emerge – and to identify the people at greatest risk of developing them.

Next steps:
The researchers will use the knowledge gained from this review to guide their work on finding ways to identify who has a higher risk of developing a brain disorder.

Larsen, K.M., Dzafic, I., Siebner, H.R., & Garrido, M.I. (2018). Alteration of functional brain architecture in 22q11.2 deletion syndrome – Insights into susceptibility for psychosis. Neuroimage. doi: 10.1016/j.neuroimage.2018.09.001

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