• Hugo Creeth

Hippocampal Shrinkage in Schizophrenic Adolescents

Schizophrenia is a psychiatric disease that causes hallucinations, memory and cognition issues. It affects approximately 0.5% of the general population, recent research has linked the disease to genetic abnormalities of chromosome 22. Specifically at 22q11.2, where a deletion at this point has been linked to six times the likelihood of developing psychotic symptoms. But what triggers the illness?

One study carried out by researchers at the University of Geneva may have provided an answer. The scientists spent years observing and analysing patients with 22q11.2 deletion syndrome, also known as DiGeorge Syndrome. They found that the size of the hippocampus was significantly smaller than normal patients, despite following the normal developmental trajectory of healthy individuals. The hippocampus is a vital part of the brain, named after the ”Sea-horse” due to its appearance, that is responsible for memory and emotions.

The discovery didn’t stop here however, what the researchers noticed was at the age that psychotic symptoms first appear, typically in adolescence, the hippocampus atrophies dramatically.

DiGeorge syndrome is a neurogenetic disorder that due to the high occurrence of psychosis in patients with the condition offers a tangible way to learn more about the causes of schizophrenic symptoms. The Geneva team followed 275 patients between the ages of 6-35 years for 18 years. They this included a control group of 135 individuals and 140 with the deletion syndrome.

They carried out MRI every three years so that they could observe brain development. The data that was produced was inputted into a sophisticated statistical model created through the use of machine learning. This model allowed the researchers to compare the development of the hippocampus in both groups of patients. Valentia Mancini, a lead researcher of the group, says the discovery that the hippocampus was smaller in those people with 22q11 deletion meant they could hypothesise that “the smaller size of the hippocampus originates in utero during its development in the womb”.

Interestingly they also noticed that one region of the hippocampus CA3 was not effected and appears to be more robust to the changes that cause this decrease in size during early life. However it was this area that underwent the greatest atrophy during the teenage years.

Currently the reasons behind this drastic atrophy of such a key brain structure are not known. The scientists have suggested reasons geared at environmental factors, such as stress and neuronal inflammation. Stress is known to increase the volume of the neurotransmitter glutamate in the brain, it is thought that this may have the effect of poisoning the hippocampus. The researchers believe that if they could target the cause of the atrophy before it is too late then there may be a new method of preventing the development of schizophrenic symptoms in these at risk individuals.

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