Studying broken chromosomes can illuminate neuroscience

It is sad, but true, that much of what is known about how human brains work has been learned by studying brains that are broken. Injuries caused by disease or accident show, from the list of functions thus disabled, the jobs of the part of the brain that has been damaged. Similarly, “injuries” to the genome, resulting in the deletion or duplication of stretches of DNA, sometimes have clear effects which can illuminate the functioning of healthy brains. At the AAAS meeting Karen Berman of America’s National Institute of Mental Health and Carrie Bearden of the University of California, Los Angeles, told participants of the latest finding concerning two of these genetic injuries.

Some segments of the genome are at particular risk of being lost or duplicated during the process of meiosis, when pairs of chromosomes swap genetic material prior to the formation of eggs and sperm. The reason is that they are flanked by stretches of DNA which have matching sequences of genetic letters. These matching flanks can confuse the molecular machinery that does the swapping. Sometimes this confusion causes the pertinent section to be left out. Sometimes the section in question ends up duplicated. Any individual inheriting a chromosome so altered will thus have either a deficiency or a surplus of the genes that are part of the affected section.