Down syndrome, also known as trisomy 21, is the most common genetic type of intellectual disability, which is usually mild to moderate in affected individuals. It occurs when a person carries an extra copy or portion of chromosome 21. Down syndrome is estimated to impact about one in 1,000 people. Researchers have now completed a very small clinical study that showed that the cognitive function of Down syndrome patients can be improved by 10 to 30 percent. The findings have been reported in Science.
"The experiment is very satisfactory, even if we remain cautious," noted study co-author Nelly Pitteloud of Lausanne University Hospital.
This work was based on previous research that has indicated that gonadotropin-releasing hormone (GnRH) production in the brain is related to cognitive functions like language, learning, and memory. GnRH helps regulate testosterone and estrogen levels, and puberty can be triggered, in part by increased GnRH levels.
"We wondered if this hormone could play any role in establishing the symptoms of people with Down syndrome," noted study co-author Vincent Prevot of the INSERM institute.
The researchers found that five microRNA molecules that control GnRH production are dysfunctional in a mouse model of Down syndrome. Cognitive defects in this model, including loss of smell or olfaction, a common symptom of Down's, were connected to abnormal GnRH release. When this model was treated with a drug that can lower testosterone and delay human puberty, cognitive function and olfaction were restored.
Next, the investigators began a trial in which seven men aged 20 to 50 with Down syndrome were treated with this drug; every two hours for six months, the drug was delivered to their arms in pulses, to mimic the action of the hormone in people without Down's.
Over the course of the trial, smell, and cognition assessments were made, and MRI scans were taken. In six of seven patients, there was cognitive improvement without significant side effects. Olfaction was not improved in anyone, however. A drawing test, in which patients were asked to draw a basic, three-dimensional bed, also showed signs of improvement after the treatment.
The study authors acknowledged that the small size of the study limits our ability to draw conclusions, and noted that patients were also "pushed by their parents." A lot more research will be needed before we know whether this approach will work as a treatment for people with Down syndrome, they said.
A larger trial that will include women is planned for the coming months.
"We are not going to cure the cognitive disorders of people with Down syndrome, but the improvement seen in our results already seems fundamental enough to hope to improve their quality of life," Pitteloud said.
Sources: MedicalXpress via AFP, Science
