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Monozygotic(MZ)twin pairs concordant for dementia of the Alzheimer type (DAT)or for proven Alzheimer's disease(AD)have a significantly higher frequency of a positive family history(DAT or AD in at least one first- degree relative,p<0.002)than do discordant MZ twin pairs,consistent with a lesser predicted distribution of proportions of surviving first-degree relatives without DAT(or AD)(p<0.001).The results suggest that concordant MZ twin pairs with DAT(or AD)have a heritable form of disease.AD in discordant twins may result from environmental influences or from a somatic chromosomal change following zygotic division. |
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