Evaluation of Patients With Unresolved Chromosome Abnormalities

Overview

The purpose of this research is to study a new way to test for chromosome abnormalities. Chromosomes are strands of DNA (the genetic material in the cell nucleus) that are made up of genes-the units of heredity. Chromosome abnormalities are usually investigated by staining the chromosomes with a dye (Giemsa stain) and examining them under a microscope. This method can detect many duplications and deletions of pieces of chromosomes and is very accurate in diagnosing certain abnormalities. It is not useful, however, for identifying very small abnormalities. This study will evaluate the accuracy of a test method using 24 different dyes for finding small chromosome abnormalities. Children and adults with various chromosome abnormalities may be eligible for this study, including, for example, people with developmental delay or mental retardation, abnormal growth features or growth retardation, and certain behavioral disorders. Participants will be evaluated in the clinic over a 1- to 3-day period, depending on their symptoms. All participants will be examined by a genetics specialist and will have a physical examination and possibly X-rays, computerized tomography (CT) scans, magnetic resonance imaging (MRI), ultrasound studies and medical photography. Blood will be drawn for chromosome testing-about 3 tablespoons from adults and 1 to 3 teaspoons from children. When the test results are available, participants will return to the clinic for follow-up evaluation and review of the test findings. The genetic and medical evaluations, along with their implications, will be discussed.

There is a range of genomic aberrations from aneuploidy down to single base pair deletions or inserts. Present technology uses microscopic cytogenetics for detection of large rearrangements (greater than 2 Mb) and molecular techniques for small rearrangements (less than 2 Mb). There is a gap in practical diagnostic technology in that microscopic cytogenetics has poor sensitivity for aberrations less than 5 Mb and the molecular techniques are cumbersome for clinical use in the megabase range. In many cases it is possible to determine that an aberration is present by microscopic cytogenetics but cannot be characterized. We propose to use Spectral Karyotyping (SKY) and supplementary FISH and molecular techniques to characterize these aberrations. Subjects will be seen in OP9 for a clinical genetics evaluation and phlebotomy for SKY. Confirmation of SKY results will be performed by standard FISH, genomic content mapping, and other standard techniques.