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Subacute sclerosing panencephalitis in only one of identical twins. A seven-year follow-up.

We report a seven-year follow-up of identical twins, in one of whom subacute sclerosing panencephalitis (SSPE) developed. Primary measles infection occurred simultaneous in both twins at age 4. The affected twin sustained a grade 1 closed head injury within six months of her primary measles infection. At age 13, SSPE was diagnosed following the onset of personality change and myoclonic seizures. Measles antibody level was elevated in the serum and CSF. After remaining in stage 2 for five years, rapid mental and neurological deterioration occurred. Measles antibody level remained elevated, and oligoclonal IgG was present in both serum and CSF. Results of neurological examination as well as virological and immunological tests were normal in the unaffected twin. Besides the occurrence of head injury, factors known to be associated with SSPE were not obviously different in the twins. We have been unable to determine a difference that would easily explain the occurrence of SSPE in only one of two identical twins.