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Why does epilepsy start at a certain age?

QWhy does primary epilepsy often present in teenagers or young adults and not before?

AMost primary brain diseases have an age-specific onset. Learning difficulties usually become evident in primary school; schizophrenia, on the other hand, presents in the late teens or early adult life, and in common with primary epilepsy has a genetic cause with environmental triggers.

The reason is the brain matures before the combined effects of genes and environment lead to obvious symptoms.

Some forms of primary epilepsy begin in childhood, such as childhood absence epilepsy (petit mal). The common form of epilepsy presenting in teens or early adult life is juvenile myoclonic epilepsy (JME). It is important to recognise this condition because lifelong treatment is usually required. Treatment is highly effective if the right drugs are used ­ lamotrigine, topiramate, sodium valproate and probably levetiracetam, but not carbamazepine or phenytoin.

JME typically begins shortly after puberty with myoclonic jerks and sometimes absence attacks, which are typically overlooked until the first tonic-clonic convulsion. Attacks often occur shortly after waking and can be triggered by alcohol and sleep deprivation. In 80 per cent of cases onset is between 12 and 18 years.

Primary epilepsy arises in deep brain structures (the diencephalon) and may relate to failure of inhibition, enhanced excitation or hypersynchronisation.

Many adults are disabled by intractable JME after inappropriate treatment because the syndrome has not been recognised.

Dr Giles Elrington, consultant neurologist, Bart's and The London NHS Trust, London

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