A cough syrup Down syndrome treatment is about to be tested in a clinical trial-- researchers say that a common cough syrup ingredient can improve learning and cognitive abilities of people with the genetic disorder. Down syndrome, the most common genetic cause of learning disabilities in children, is caused by an extra chromosome in DNA called trisomy 21. The World Health Organization estimates that people with Down syndrome account for more than 1 of every 1,000 births- 6 million people- worldwide. Early intervention programs can help meet affected children’s needs, but drug interventions, like the cough syrup Down syndrome treatment being tested, may be more easily applied to underserved populations.