Onset of symptoms: usually from 4 to 6 months of age
Clinical findings:
(1) marked irritability with insomnia
(2) psychomotor retardation, neurodevelopmental regression
(3) cerebellar ataxia
(4) ascending pyramidal tract signs affecting the legs
(5) decelerating head growth
(6) choreoathetosis, ballismus and other dyskinesias
(7) hypotonia
(8) seizures (variable)
(9) response to oral folinic acid therapy
Complications that develop during childhood:
(1) optic atrophy with blindness
(2) hearing loss
Laboratory findings:
(1) normal folate levels in serum
(2) normal folate levels within erythrocytes
(3) low levels of 5-methyltetrahydrofolate (5MTHF) in the cerebrospinal fluid
(4) presence of serum autoantibodies against the folate receptor
