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Researchers in Australia and the US have found further evidence that
some types of epilepsy may be inherited. Their work, reported last month
at a meeting of the American Academy of Neurology in Boston, is based on
studies of young twins and adults with the disease.

Samuel Berkovic, from the University of Melbourne and the city’s Austin
Hospital, says pairs of identical twins are more likely to suffer from seizures
than fraternal, or nonidentical, twins. He and his colleagues studied 219
pairs of Australian twins, in whom one or both suffered from seizures. They
sorted the twins into categories by the type of seizure they suffered.

The term ‘epilepsy’ covers a wide range of conditions affecting the
brain. In some people, the abnormal electrical activity that characterises
the disease is confined to one area of the brain, while in others it is
generalised to the whole brain. Seizures can be as mild as a short loss
of responsiveness, known as petit mal, or as severe as grand mal fits. Sometimes
brain damage results in epilepsy, especially in the localised form of the
disease.

Of the 219 pairs of twins, Berkovic and his colleagues found 51 pairs
who suffered generalised epilepsy; 26 of them were identical twins, the
remainder fraternal. Of the identical twins, 17 pairs, or 65 per cent, both
suffered seizures. By contrast, the researchers found that only 5 of the
25 pairs of nonidentical twins were both affected.

The team studied the 51 pairs of twins further. Thirty-four pairs had
no known brain damage or other noninherited factors that could explain their
epilepsy. Of this subgroup, 17 pairs were identical twins. Most of the identical
twins had the same kind of seizures as each other, and were both affected.
The researchers found the same specific abnormalities in the electrical
trace of the brain’s activity in three other pairs of the 17 where one had
fits and the other did not. By contrast, both twins suffered seizures in
only 4 of the 17 pairs of fraternal twins, and only one pair suffered the
same type of seizure.

The fact that most of these identical twins suffer the same type of
seizure suggests that they may have a distinct, genetically determined syndrome,
says Berkovic. But he doubts that a single gene is involved, suggesting
instead that two or more may interact to cause the condition. He believes
the types of epilepsy that may be inherited are largely benign, and disappear
when an individual reaches adulthood.

In a second project, David Treiman from the University of California,
Los Angeles, studied the family histories of adults treated for localised
epilepsy. He found the disease was clustered into families. Treiman believes
that genetic factors may increase susceptibility to the disease, making
some people more vulnerable than others to developing epilepsy following
injury.