HIPPOCAMPAL SCLEROSIS STUDIED IN IDENTICAL-TWINS

Objective: To test both the genetic and acquired hypotheses for the et iology of hippocampal sclerosis (HS) by studying with optimized and qu antitative MRI three monozygous (MZ) twin pairs in which the index twi n had temporal lobe epilepsy and HS. Background: There is conflicting evidence in the literature regarding whether PIS is genetic or acquire d prenatally, perinatally, or as a consequence of prolonged childhood seizures, Methods: We compared three MZ pairs with 30 age-matched cont rol subjects who had no history of a neurologic disorder; we also used the twins as matched samples to assess subtle differences between the affected and the unaffected twins. Results: All of the affected twins had prolonged seizures with fever in early childhood, which stood out as the unique factor common to all affected twins and was absent in a ll the unaffected twins. HS was present in all affected twins but was absent in the unaffected twin on visual, volumetric, and T2 relaxometr y criteria. Comparison of the affected twin with the co-twin revealed that intracranial volume ipsilateral to the HS was relatively small in two of three affected twins. Conclusions: The absence of HS in the un affected twin is strong evidence against a genetic hypothesis for PIS. Neither perinatal problems nor birth order were factors in determinin g the presence of HS. This twin study supports the notion of WS as an acquired lesion secondary to prolonged seizures in early childhood and suggests that regional abnormalities of intracranial volume are assoc iated with HS.