LKS have what is known as auditory agnosia, whereby they experience a loss of language understanding, and which also severely limits speech. A wide range of additional symptoms are found, including problems with social communication (see entry Autism Spectrum disorders, including Asperger syndrome), a reduction in learning abilities (see entry Learning Disability), and in more than half of cases, difficulties with coordination of walking, feeding and hand function. Many children also have behaviour problems, including impulsivity, hyperactivity, distractibility and behaviour that challenges.
Three quarters of children with LKS also have epileptic seizures (see entry Epilepsy), though a significant minority do not at least initially have obvious seizures. All, however, show epileptic activity on electroencephalogram (EEG) in the central region of the brain (temporal lobe: language reception); this activity is particularly increased during sleep, which is a key symptom of the condition.