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Jan. 24, 2012

Causes of Biopolar Disorder

by Mariel Emrich

Click to enlarge images

DNA Deletion

By Mariel Emrich, Columbia Grammar and Preparatory School

Bipolar disorder is a condition in which people have mood swings. They have periods of happiness and periods of depression. Doctors are unsure what causes bipolar disorder. However, it is clear that bipolar disorder is carried down genetically, since the disorder runs in families.

New research in 2011 suggests that rare copy number variants (CNVs) where sections of DNA are either duplicated or missing seem to play a major role in the risk for early onset bipolar disorder. This study was conducted by University of California, San Diego (UCSD) School of Medicine and published online in the journal Neuron.

CNVs are a type of mutation or alteration in the genome where cells end up with an abnormal number of copies of sections of DNA code. This may mean too few copies, due to deletion, or too many, due to duplication. CNVs can be inherited, or de novo -- spontaneously occuring either in the sperm or unfertilized egg, or even in the egg after it has been fertilized.

Past studies have shown that rare CNVs add to the risk for some neuropsychiatric disorders, such as schizophrenia and autism. However, it has not been clear if rare CNVs play a role in bipolar disorder. Previous studies have focused on inherited variants as opposed to finding the key genes that cause this disorder.

In this study, researchers performed a genome-wide analysis of de novo CNVs in parents and offspring. 185 of the offspring were diagnosed with bipolar disorder, 177 with schizophrenia, and 426 were healthy controls. The analysis showed that de novo CNVs occurred at a much higher frequency in participants with bipolar disorder than in the control group. There was a significantly higher number of de novo CNVs in patients younger than 18 years old.

The researchers found that de novo CNVs' contributed to significant genetic risk in about 5% of the cases of early onset bipolar disorder.

In an article in Medical News Today, Jonathan Sebat, assistant professor of psychiatry and cellular and molecular medicine at UCSD’s Institute of Genomic Medicine, and Dheeraj Malhotra, an assistant project scientist in Sebat’s lab, explained that this study proves that having a de novo mutation increases the chance of having an earlier onset of the disease. However, this is not enough to point to a specific gene or region of the genome that is related to bipolar disorder. Malhorta pointed out that you would have to sequence whole genomes from a large number of families with bipolar disorder before you could identify all the de novo CNVs that might be involved.

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Mariel is currently a sophomore at Columbia Grammar and Preparatory School in New York City. She loves learning about science and particularly enjoys genetics, cancer research, radiology, and forensics.

About Mariel Emrich

The views expressed are those of the author and are not necessarily those of Science Friday.

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