So I too went out and googled Landau Kleffner Syndrome:
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What are the main symptoms?
All children with LKS have abnormal electrical activity in one, sometimes both temporal lobes, the area of the brain responsible among other functions for processing language. This epileptiform activity shows up in an EEG test particularly when the child is asleep.
About two-thirds of LKS children have seizures. Seizures during the night are common. Many children have very few seizures and these are readily controlled by anti-epileptic drugs. Some children never have obvious seizures: it is not necessary to have a seizure to have LKS. A few children have many seizures which are harder to control.
The language disorder in most children affects comprehension or understanding. Many LKS children become unable to understand their own name. They are also likely to have difficulty recognising environmental sounds such as the telephone ringing. These children may appear to be deaf.
Expressive language - the ability to speak is often seriously affected; some children lose their speech completely. Rarely, a child may be able to understand language, but have difficulty with speaking.
Behavioural problems are common, especially hyper-activity, poor attention, depression and irritability.
Some children have episodes of very abnormal "autistic type behaviour" with symptoms such as avoidance of contact with family and friends (avoidance of eye contact is common) extreme pickiness over food, very disturbed sleep, attacks of rage and aggression, insensitivity to pain, bizarre and inappropriate and repetitive play.
There may be temporary other neurological problems such as loss of bladder and bowel control, episodes of visual disturbances may occur, the child can see but does not understand what he sees. He may have difficulty recognising family and friends or common objects, such as food and clothes.
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How exactly do the symptoms differ from getting old?