It develops into a progressive neurodegenerative disorder effecting babies although when new born they may develop quite normally for the first few months. Loss of head movement occurs at 6 to 8 months together with an exaggerated startle reaction. Other symptoms consist of sickness excessive drooling inability to roll over or sit up and a general rigidity. By the age of two the head has become enlarged and the child is blind. Life expectancy is not beyond 5 years.