Abstract
Karyotype analysis on amniotic fluid samples or chorionic villi has limited resolution and there is a delay between sampling and results. Therefore, invasive prenatal diagnosis has been reserved for pregnancies that are at increased risk for a defined genetic disorder, or for common aneuploidies found in liveborns. However, more than 70 disorders are now known to be associated with birth defects or developmental problems that are caused by deletion or duplication of a small chromosomal segment. These conditions and aneuploidies can be detected by array-based comparative genomic hybridization (CGH), which can evaluate the copy number of thousands of genomic regions simultaneously in a single assay. We review current knowledge on benign and pathological genomic copy number variants, principles of array CGH and its use for discovery and diagnosis of genetic diseases. Array CGH has already revolutionized genetic diagnosis in children and adults and is being used increasingly for prenatal diagnosis.