| Main clinical features
|
in neonatal phenotype, presenting in the first few days of life with lethargy, hypotonia, and myoclonic jerks, and progressing to apnea, and often to death; patients who regain spontaneous respiration develop intractable seizures and profound mental retardation
in the infantile form, patients present with seizures and have various degrees of mental retardation after a symptom-free interval and seemingly normal development for up to 6 months
in the mild-episodic form, patients present in childhood with mild mental retardation and episodes of delirium, chorea, and vertical gaze palsy during febrile illness
in the late-onset form, patients present in childhood with progressive spastic diplegia and optic atrophy, but intellectual function is preserved and no seizures |