Seizures can also take a mixed form, with staring spells and momentary lapses of attention. Seizures can be controlled with standard anti-convulsant medication. The most common involvements of the nervous system in Down syndrome are hypotonia, atlantoaxial dislocation and seizures. The reduced muscle tone of hypotonia affects most infants with Down syndrome and ranges from mild to severe. Atlantoaxial dislocation refers to a weakness of neck muscles that affects approximately 10 to 20 percent of children with Down syndrome.
Most cases are asymptomatic.
Preventive measures against neck injuries call for lateral cervical x-rays for all children with Down syndrome after age two. If atlantoaxial dislocation is present, high-risk activities such as jumping, diving, etc., should be limited. In cases of atlantoaxial dislocation where symptoms are present, the atlantoaxial joint can be surgically fused. Seizures are equally common in the child with Down syndrome as compared to the general same-age population. After age 20, the incidence of seizures in the Down syndrome population increases substantially as compared to the general population.