Apolipoprotein E genotype and hippocampal asymmetry in Alzheimer's disease: a volumetric MRI study

Asymmetry of brain structures is common to many species and is even present in utero. Some developmental, pathological, and dementing diseases are ass ociated with alterations in normal anatomical asymmetries. Anatomical asymm etries, however, have been only superficially studied in Alzheimer's diseas e. Recent evidence indicates that the allele epsilon 4 of the apolipoprotei n E (ApoE), a well known risk factor for Alzheimer's disease, might play a part in determining some brain morphological changes both in normal carrier s and in patients with Alzheimer's disease. This study evaluated the effect of the ApoE genotype on hippocampal asymmetry in patients with Alzheimer's disease carrying 0, 1, and 2 copies of the allele. Volumetric right-left d ifferences of the hippocampi were computed in 28 right handed patients with Alzheimer's disease (14 -/-, 9 epsilon 4/-, and 5 epsilon 4/4) and 30 cont rols without detectable cognitive deficit. In controls, the right hippocamp us was larger than the left, whereas in patients with Alzheimer's disease t his asymmetry was progressively reduced with increasing gene dose of the ep silon 4 allele, and asymmetry was reversed in the epsilon 4/4 Alzheimer's d isease group. The mean right-left volume differences were: 1.2, 0.7, 0.2, a nd -1.0 in controls, -1-, epsilon 4/-, and epsilon 4/4 patients, respective ly (sex adjusted p for trend=0.017). The data indicate a dose dependent eff ect of the ApoE epsilon 4 allele on hippocampal volume asymmetry in Alzheim er's disease.