The following information may help to address your question:
Researchers are making great strides in identifying the genes on chromosome 21 that cause the characteristics of Down syndrome. Many believe that this research is the key to improving, correcting, or even preventing many of the problems associated with Down syndrome.
Some of the most promising Down syndrome research involves gaining a better understanding of the genetic, biological, and neurological (involving the nervous system) processes and how they relate to one another to cause intellectual impairment. Researchers are most interested in the part of the brain called the hippocampus. The hippocampus is essential for learning and memory. They think that an abnormality in the hippocampus causes the delay of intellectual development in individuals with Down syndrome.
Researchers believe that the increased activity (expression) of one or more genes on chromosome 21 causes the structure and function of the hippocampus to be abnormal. Individuals with Down syndrome have some overactive genes because they have an extra copy of chromosome 21. They are currently trying to identify the specific genes that cause these abnormalities and how increased activity of these genes affects intellectual ability. The next step will be to identify treatments that can turn down or turn off these genes in the brain with the hope of restoring the brain to normal function.
The Down Syndrome Research and Treatment Foundation has a FAQ addressing current research into Down syndrome.
ClinicalTrials.gov lists trials that are studying or have studied Down syndrome. Click on the link to go to ClinicalTrials.gov to read descriptions of these studies.
The National Down Syndrome Society provides information about research related to Down syndrome.