Chromosome 9p deletion is a chromosome abnormality that occurs when there is a missing (deleted) copy of genetic material on the short arm (p) of chromosome 9. The severity and the signs and symptoms depend on the size and location of the deletion and which genes are involved. Features may affect many parts of the body and may include developmental delay, low muscle tone (hypotonia), distinctive facial features, heart conditions, scoliosis, and/or genital abnormalities. Chromosome testing of both parents can provide more information on whether the deletion was inherited. In about half of cases, the deletion occurs sporadically and neither parent has a chromosome abnormality. In the other half, one parent is found to have the same deletion (possibly with no features) or a balanced translocation (which usually does not cause any features).