"For years, many children who have multiple congenital problems, such as developmental delays, heart defects and facial abnormalities, have gone undiagnosed because they may not have an easily recognizable syndrome," said study leader Tamin H. Shaikh, Ph.D., a molecular geneticist at The Children's Hospital of Philadelphia.
"Until recently, our laboratory technology was not sufficiently refined to detect many of these small rearrangements in chromosomes," added Dr. Shaikh. "Now we have a better tool for finding the abnormal gene or genes that give rise to a disorder." The research is published in the May 2006 issue of Human Mutation.
For many of these rare disorders caused by small errors in chromosomes, improved diagnosis does not mean that physicians can provide more effective treatments, at least not immediately. In the long run, adds Dr. Shaikh, better knowledge of the underlying genetic cause of a disease may provide targets for designing future therapies.
Conventional genetic tests have limited resolving power in detecting many chromosomal arrangements. In karyotyping, chromosomes are stained and examined under microscopes, but only larger rearrangements are visible, such as extensive deletions, or the presence of an extra chromosome, as occurs in Down syndrome. Another technique, subtelomere analysis, finds smaller, submicroscopic abnormalities, but only in the regions directly below the telomeres, at the end of each chromosome.
Recent advances in diagnostic gene chips, used by Dr. Shaikh's team, allow more precise analysis of very small
Contact: John Ascenzi
Children's Hospital of Philadelphia