Last week, scientists claim to have come closer than ever before in their effort to understand the cause of schizophrenia. The unprecedented study (undertaken by scientists from Harvard Medical School, Boston Children’s Hospital and the Broad Institute) attempts to delve into the biology behind schizophrenia, often assumed to be a purely psychiatric disorder.
Two million Americans have been diagnosed with schizophrenia, a condition that counts delusional thinking, hearing voices and hallucinations among the symptoms.
Drugs that treat the condition only temper these symptoms but cannot treat the cause of the problem.
“They did a phenomenal job. This paper gives us a foothold, something we can work on, and that’s what we’ve been looking for now, for a long, long time,” said professor of genetics at Columbia University, David B. Goldstein, who had been critical of other prior studies that tried to link genetics with psychiatric problems.
The researchers have isolated the genes that increase the likelihood of getting schizophrenia.
Synaptic pruning is a process where the brain “prunes” away weak and redundant connections between neurons as it ages.
Between adolescence and young adulthood, the part of the brain where thinking and planning skills are processed is where most of this synaptic pruning occurs.
Although it occurs as a natural part of maturation, those with genes that accelerate the pruning are at a greater risk of developing schizophrenia according to the study.
People with schizophrenia have been shown in previous studies to have a decreased quantity of neural connections; this led scientists to believe that pruning was linked to the disorder. This hypothesis is strongly supported by the new study, which also describes the process that causes pruning to go wrong, why it occurs and the genes that cause it.
The gene variant in question acts like an over-ambitious lumberjack, aggressively “tagging” connections for pruning.
Other scientists have warned against prematurely rushing to conclusions.
“This work is extremely persuasive, but any step forward is not only rare and unusual, it’s just one step in a journey of a thousand miles”, said Dr. Samuel Barondes.
The MHC section of the human genome has been shown by previous studies to be the most correlated to the prevalence of schizophrenia. It is here where the research team started their search, the section that is also known to control the body’s immune response.
The body’s immune response acts by tagging invading bacteria for destruction, and this has caused scientists to speculate that schizophrenia was somehow caused by the body harming itself.
The research team found that this was not exactly the case; the MHC section contains four variants of the C-4 gene. The variants produced the C4-A and the C4-B protein in different quantities, with differing lengths of the genes also contributing to the discrepancy.
Schizophrenic individuals were found to be more likely to produce more C4-A than normal test subjects.
“C4-A seemed to be the gene driving risk for schizophrenia,” Dr. Steven McCarroll, leader of the research team, said, “but we had to be sure.”
The team found that mice bred without the C-4- producing genes showed symptoms of synaptic pruning gone awry.
Dr. Beth Stevens who conducted tests on the mice said that “the evidence strongly suggested that too much C4-A leads to inappropriate pruning during this critical phase of development.”
Too much C4-A means too much pruning, and explains the decreased neural connections and prevalence in teenagers or young adults.
“The finding connects all these dots, all these disconnected observations about schizophrenia, and makes them make sense,” Dr. McCarroll said.
Correlation is not causation however; having a gene variant that causes excessive pruning on its own does not cause the occurrence of schizophrenia in all cases- several other factors are at play, and in fact, it only increases one’s risk by 25%… from 1% to 1.25% among the general populace.
Among young people who show early symptoms of developing the disorder, however, it is hoped that genetic biomarkers could be discovered from their genetic profile that would aid in making a more accurate diagnosis of the likelihood of the early symptoms turning into full-blown schizophrenia.
“We’re all very excited and proud of this work,” Dr. Lander, director of the Broad Institute, said. “But I’m not ready to call it a victory until we have something that can help patients.”
Sources: The New York Times, Scientific American
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