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well-recognised syndrome of epilepsy, hippocampal sclerosis and febrile convulsions is
associated with common genetic variation around the SCN1A gene32.

Prenatal factors
Maternal ill-health, parental sub-fertility19, prenatal maternal cigarette smoking26 and alcohol
intake have been associated with the occurrence of febrile convulsions in the offspring.
However, population-based studies do not find much evidence that social and maternal
factors are significant7,13,26.

Perinatal factors
A hospital-based series suggested that an abnormal pregnancy or birth history predisposes to
febrile convulsions in general and complicated initial febrile convulsions in particular19. In
contrast the population-based American NCPP26 found that pregnancy and birth factors
contributed little to the risk of febrile convulsions.

Precipitating factors
The height or duration of the fever may be important but there are problems in evaluating the
temperature recordings because febrile convulsions usually occur randomly at home. Viral
infections commonly cause the fever that is associated with febrile convulsions. Synthesis of
immunoglobulin in the CSF of children with febrile convulsions has been demonstrated,
suggesting that encephalitis may sometimes occur and not be recognised19. There is evidence
that human herpes virus-6 (HHV-6) is linked with exanthem subitum, a condition that is
frequently complicated by febrile convulsions33. More recent work suggests that acute HHV-
6 infection is a frequent cause of febrile convulsions in young children that do not have the
signs of exanthem subitum34. HHV-6B infection has been shown to be commonly associated
with febrile status epilepticus, HHV-7 less frequently so. Together they accounted for one-
third of the cases in a study of febrile status epilepticus, a condition associated with an
increased risk of both hippocampal injury and subsequent temporal lobe epilepsy35.

Bacterial infections may be associated with febrile convulsions  urinary tract infections,
shigella and pneumococcal bacteraemia, for instance. Children with bacterial meningitis
sometimes have convulsions and it is important to remember this when deciding whether or
not to perform a lumbar puncture.

It has been shown that there are increased risks of febrile seizures on the day of receipt of
DPT vaccine and 814 days after MMR vaccine, apparently not associated with long-term
adverse consequences36. A study in the UK found that 6–11 days after MMR vaccine there
was an increased risk of complex febrile convulsions lasting more than 30 minutes37.
However, a Danish study found that the increased risk of febrile convulsions after MMR
vaccination was small and transient. Also the long-term rate of epilepsy was not increased in
children who had febrile convulsions following MMR vaccination compared with children
who had febrile convulsions of a different aetiology38.

Outcome after febrile convulsions

In 1971 Taylor and Ounsted39 wrote: ‘We think that the convulsive hypoxia sustained during
prolonged febrile convulsions causes the death of vulnerable neurones in the cerebellum, the
thalamus, and in mesial temporal structures’.