The infantile form generally appears by age two, with features including megalencephaly (large head), developmental delay, persistent vomiting, weight loss, seizures, muscle stiffness and reduced movement. Hydrocephalus (water on the brain) may be present, sometimes picked up by antenatal ultrasound scans.
The juvenile form appears slightly later, around 3-12 years old, with trouble speaking or swallowing, possibly psychiatric problems, but rarely seizures.
The adult form is the most varied and can occur from 13-70 plus. Symptoms may appear gradually, and include difficulty eating or speaking, very early or late puberty, deterioration of cognition (reasoning, memory or attention), changes in walking pattern, palatal myoclonus (spasm of the roof of the mouth), nystagmus (uncontrolled eye movements), sleep apnoea, bowel or bladder problems, and kyphoscoliosis (curving of the spine). Some adults are misdiagnosed with Multiple Sclerosis (MS) or Alzheimer's Disease.