By Dr. Charles A. Williams, Professor of Pediatrics and Genetics, Division of  Genetics and Metabolism, Department of  Pediatrics, University of Florida, Gainesville, FL In the last edition, I reviewed the four genetic mechanisms that can disrupt the Angelman syndrome (AS) gene: chromosome deletion, imprinting defect, mutation in UBE3A and paternal uniparental disomy. When an individual with AS has one of these defects, it is typically present in every cell of the body, since the defect existed at the time of conception when the sperm and egg fused to form the first cell of the embryo. All of the subsequent cells are thus derived from this original cell. It is possible…