Homozygotes show mild developmental delay in early childhood, delayed walking with unstable gait, tremor, speech delay and strabismus. In the teenage years, main features are cerebellar ataxia, intellectual disability, memory difficulties and affective emotional issues, such as anxiety and mood instability. Comorbid seizures in childhood may lead to a more severe phenotype, including prominent psychiatric symptoms, such as inappropriate laughing, social closure, and hallucinations, and severe intellectual disability. Additional features are dysarthria or scanning speech, nystagmus, postural and intention tremor, dysmetria, dysdiadochokinesia, ataxic gait, poor coordination, mild muscle weakness with hyperreflexia, scapular winging, lumbar hyperlordosis, dorsal hyperkyphosis, and flat feet.
Heterozygotes show a milder phenotype, including normal cognitive function to hallucinations, mood alterations, aggression, psychomotor agitation, insomnia, anxious/depressive disorder and restless legs syndrome.
ADGRB3