Down Syndrome (cont.)

Medical Author:

Sietske N. Heyn, PhD

Sietske N. Heyn, PhD

Sietske N. Heyn is a medical writer with a PhD in neuroscience. Dr. Heyn's education includes a BS with honors from the University of Oregon, and a doctoral degree in neuroscience from the University of California at Davis. After completing postdoctoral training at the University of California, San Francisco, and many years of working as a medical writer at the Stanford University Center for Down Syndrome Research, Dr. Heyn now runs her own medical writing business.

View Full Profile

Medical Editor:

David Perlstein, MD, MBA, FAAP

David Perlstein, MD, MBA, FAAP

Dr. Perlstein received his Medical Degree from the University of Cincinnati and then completed his internship and residency in pediatrics at The New York Hospital, Cornell medical Center in New York City. After serving an additional year as Chief Pediatric Resident, he worked as a private practitioner and then was appointed Director of Ambulatory Pediatrics at St. Barnabas Hospital in the Bronx.

View Full Profile

Down Syndrome Symptoms (the Effects of Trisomy 21)

It is now well known that the extra genes on the additional chromosome 21 are the cause of Down syndrome. Scientists are trying to determine which of the genes on chromosome 21 cause different characteristics of the disorder when present in three copies. Some genes may be more active and others less active due to the extra copy, and some of the genes may have a stronger influence on the characteristics of Down syndrome than others. Currently, about 400 genes on chromosome 21 have been identified, but the function of most remains unknown.

Until recently, scientists hypothesized that the most important genes involved in Down syndrome were located in an area on chromosome 21 called the Down syndrome critical region. However, scientists have found that genes outside this region are also important in Down syndrome.