However, parents noticed significant deterioration in his speech, behavior, and cognition since the age of 2½ years. He became socially withdrawn.
[annalsofian.org]
They have retinal degeneration, abnormal involuntary movements (myoclonic and dystonic), rapid speech and motor deterioration, and less prominent seizures.
[omicsonline.org]
It is characterized by rapid deterioration with psychomotor retardation, loss of speech, seizures, ataxia, blindness, hypotonia, microcephaly, and occasional convulsions.
[icd10data.com]