History of Down Syndrome Cognitive Research

In 1866, John Langdon Down, a British doctor, first described the characteristics of people with Down syndrome.

In 1959, Dr. Jérôme Lejeune discovered the chromosomal abnormality linked to Down syndrome. Persons with Down syndrome exhibited an extra copy of chromosome 21.

The exact mechanism by which the presence of this additional genetic material resulted in the cognitive impairment associated with Down syndrome remained unclear, hindering the development of medical therapies.  Nonetheless, the quality of life for individuals with Down syndrome improved tremendously in subsequent decades, as a result of improved health care, expanded educational and community opportunities, and the support of families and advocacy groups.  The life expectancy of those with Down syndrome more than doubled, highlighting the importance of the need to attain skills essential for independent living.

Yet, over these intervening years, Down syndrome cognitive research had been largely lacking because many in the medical field and those in the agencies that supported them with funding had considered the problem too complex. The thinking was that little could be done to alter the impact on cognition imparted by the extra chromosome 21 in individuals with Down syndrome. Supporting this argument was the assumption that cognitive impairment is permanent, as it develops very early in development.

In recent years, however, through the availability of mouse models, and because of our remarkably increased knowledge of the human genome, and, specifically, the genes coded on chromosome 21, research into Down syndrome and cognitive impairment has been rapid and significant. Evidence using mouse models points to learning and memory defects arising from, in some cases, over- expression of certain genes. Trisomy of such genes on human chromosome 21 may impact multiple learning pathways because of impaired neuronal and synaptic signal transport. Scientists have also uncovered other pathways altered in Down syndrome, including neuronal system development, instructions necessary for neurons to “thrive”, and links between Down syndrome and Alzheimer's disease. Researchers are studying the impact of therapeutic compounds on memory and learning in mouse models of Down syndrome. The identification of neurobiological pathways that are affected by the presence of additional genetic material now provides a rational basis for the development of drug therapies to address the cognitive impairment associated with Down syndrome. These recent breakthroughs will translate into safe and effective, approved therapies to treat the cognitive impairment in individuals of all ages with Down syndrome.