Usually normal development until age 1 year followed by regression of language milestones,
with appearance of fine tremor of the hands, ataxic gait, and loss of purposeful movement
of the hands, which may not appear until the girl is 2 to 3 years old. Autistic
behavior becomes evident at this stage. Rupture of head growth becomes evident and is
known as “acquired” microcephalia. The disease is also marked with generalized
tonic-clonic seizures that are well-controlled by antiepileptic drugs, peculiar sighing
respiration, and periods of apnea. There are associated vasomotor disturbances of the
legs. After the initial neurological degradation phase, the disease appears to
plateau (between 6 and 18 months of age) followed by a rapid regression that stays
for a few weeks to a few months. It is followed by stabilization for a few years and,
finally, by a long phase of motor deterioration with loss of ambulation. Clinical features
can also involved heart (prolonged QT interval and T-wave abnormalities), respiratory system (periodic apnea while awake or hyperventilation, breath holding), GI (constipation, gastroesophageal reflux, cachexia), muscles and skeleton
(scoliosis, kyphosis, small feet, vasomotor disturbance with cold feet, muscle
wasting).