Chronic granulomatous disease occurs when a specific gene from both parents passes to the child. This gene causes phagocytic cells to develop abnormally in the immune system. Phagocytic cells normally kill bacteria. With this disease, these cells cannot work properly. As a result, the body can not fight some types of bacteria. It also makes infections likely to return.

CGD is a rare condition.

The disease is caused by one of four genes. Three of the genetic defects are recessive. This means two of these defective genes have to be present for the disease to develop—one from each parent. The other gene is located on the X chromosome. It is transmitted from mother to son.