Tay-Sachs disease
Infants with the Tay-Sachs gene from both parents usually die of pneumonia or other infections during their first four years of life. Some symptoms include: lack of energy, loss of vision and motor skills (paralyzation), and seizures.  Tay–Sachs disease is usually first noticed in infants around six months old. They show an abnormally strong response to sudden noises or other stimulus. This is called the "startle response". The child may also be listlessness or have muscle stiffness (hypertonia). The disease is classified into several forms, which are based on the age when the neurological symptoms began. There is no known treatment for this disease.