This means that two copies of the misspelled HSS gene, one from each parent, are necessary in order for the disease to occur. Males and females are equally likely to be affected. In some families, the condition can be diagnosed early in pregnancy. The main feature of HSS is iron deposits in the brain. Symptoms may include night blindness, muscle spasms, difficulty speaking, seizures, uncontrolled writhing movements and tremors.
Most victims eventually lose all muscle control and are left unable to walk, talk, or chew food.
The tragedy is compounded because HSS often strikes in childhood. The presenting signs or symptoms may include difficulty with walking or balance or problems with speech. Some children have delays in their general development from infancy. Others acquire the disease as toddlers, or even later. Regardless of when the first signs of HSS occur, the condition is always progressive.