The first strides have been made in trying to better understand Down syndrome, along with the hopes of finding ways to help those born with it.
Down syndrome, also referred to as trisomy 21, is caused by a genetic abnormality that results in a person being born with three copies of chromosome 21 or an extra piece of this chromosome, instead of the usual two. However, it was never known how this extra chromosome works in the body to cause the symptoms of the syndrome. Now, researchers have determined what seems to be one impact that this extra chromosome has on the body.
Much research on Down syndrome has focused on chromosome 21 as a whole, but Dr. Ahmad Salehi and colleagues from the department of neurology and neurological sciences at Stanford Medical School, looked at the particular impact of having extra copies of one gene that is found on this chromosome.
"In this sense, instead of targeting Down syndrome as a whole, we can start with the most disabling features of Down," said Salehi, who cited the slow mental decline that is characteristic of the disease.
Down syndrome occurs in one in every 733 live births in the United States and the risk of having a child with the disorder increases with the mother's age. Down syndrome causes several distinct physical abnormalities as well mild-to-moderate mental retardation, which can make socialization and education a bit of a challenge, but still manageable. Over the course of time, however, many people with Down syndrome go on to develop dementia, which closely resembles early-onset Alzheimer's disease.
It is this symptom of Down syndrome that was the focus of Salehi's study.
In the study, published in Neuron, researchers looked at mice with Down syndrome and found that each had three copies of a particular gene, called App. These mice also had a neurological problem that caused a decrease in their ability to transport a particular protein needed for the survival of some neurons important in learning and memory. It is believed that this neurological problem is caused by the extra App gene and, ultimately, causes some neurons to shrink, leading to the dementia that affects people with Down syndrome.
In fact, previous research has linked a mutation in the App gene to early-onset Alzheimer's disease as well. "Mutations in the App gene generally lead to a form of early onset Alzheimer's disease," said Salehi.
With this new information about how the App gene affects the cells, Salehi suggests that it may be possible to find the mechanism by which App causes neurological damage. Then, a treatment may be developed to target this process and either slow down or stop this cognitive decline in people with Down syndrome.