Hippocampal involvement in identical twins with neurofibromatosis type 1

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Abstract
Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder due to a defect on the long arm of chromosome 17. Since 1986, when Cohen et al 1 first drew attention to changes on MRI in NF1, it has increasingly been recognised that up to 75% of children with NF1 have lesions, seen most often in the brain stem, cerebellum, optic tracts, and basal ganglia.2 They are asymptomatic, usually less prominent with age, and the limited available postmortem data suggest that they involve areas of spongiotic or vacuolar change.3It is unclear how often temporal lobe structures are involved and figures range from 0% to 16%.4 5 We report on a pair of identical twins with NF1, with prominent bilateral changes in hippocampal MRI, one of whom presented with a major amnesic syndrome. The twins, aged 15, were the only children of non-consanguineous unaffected parents with no known family history. Twin 1 had been considered bright throughout his schooling, until in summer 1999 he was involved in a …