People with startle disease have an exaggerated startle reflex in response to noise and touch, followed by muscle stiffness, which can cause breathing problems and even sudden infant death syndrome (SIDS).iew full size image. We all jump at an unexpected noise or touch, but in some people, this startle response is exaggerated, and can cause falls and even death. Now, researchers in the United Kingdom have found new genes for this rare disorder, known as startle disease, or more formally as hyperekplexia.