The majority of cells in our bodies contain a nucleus, and within each nucleus there are twenty-three pairs of chromosomes. One chromosome from each pair is inherited from our mother and the other from our father.

Chromosomes are highly organised structures that contain our DNA, the genetic code from which we are made. Humans have approximately 30,000 different genes within their DNA (known collectively as the genome) and each gene has two parts called alleles. One allele for a particular gene is found on a chromosome inherited from our mother, and the other is found at the same point on the corresponding chromosome inherited from our father.

Sometimes people have chromosome abnormalities, for example part of a chromosome may be missing (deleted) or defective, or there may be duplication of genetic material; and these abnormalities can lead to a wide range of genetic disorders. A major area of research involves finding the specific genes responsible for medical conditions, so that effective screening methods and treatments can be developed.

A group of scientists at the Duke University Medical Centre, in North Carolina, have recently found evidence that people who are missing a specific section of DNA from chromosome pair 16 (referred to simply as chromosome 16), are significantly more likely than others to develop a seizure disorder during their lifetime.

Previous studies have already shown that deletion of the genes in this region of chromosome 16 can increase the risk of schizophrenia, mental retardation and, more recently, generalised epilepsy; but this research links the deletion to a much broad range of epilepsy disorders.

The team took DNA from 3,812 people with a wide range of epilepsy syndromes and compared it to the DNA of 1,299 healthy volunteers. Using advanced techniques they screened the entire genome of each person, looking for deletions or duplications of particularly long stretches of DNA.

The scientists discovered that 23 of the people with epilepsy had a deletion in the same section of chromosome 16. No significant deletions were seen in any of the healthy controls. In the epilepsy group, the region of chromosome 16 that had been deleted contained seven genes, and the researchers found that in each affected person, at least one of the two alleles from each gene had been shut down.

During the study the team observed that, although the 23 people in the epilepsy group had very similar sized deletions on chromosome 16, they sometimes presented with very different types of epilepsy. Additional analyses were therefore performed in 10 of the 23, to see if the scientists could uncover any mechanisms that explained the development of one type of epilepsy rather than another. However their results were inconclusive.

The finding that 23 out of 3,812 people with epilepsy carried the deletion, although just over half a percent, is important, because there are hundreds of different causes of epilepsy, and so that level of correlation between 23 people (a specific deletion on a specific chromosome) warrants further investigation.

A lot more research in this field is necessary, because although this deletion is now linked to schizophrenia; mental retardation and broad range of epilepsy disorders; the biological pathways that lead to one condition rather than another are unknown. Once the factors that link these disorders are understood, scientists will potentially be able to screen for the deletion and, hopefully, prevent the development of these conditions in the future.

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