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• To evaluate whether probands from a clinical sample diagnosed as having DSM-III schizotypal and/or paranoid personality disorder have a familial relationship to the schizophrenia-related disorders, the morbid risk for schizophrenia-related disorders and other psychiatric disorders were evaluated in the first-degree relatives of patients with schizotypal and/or paranoid personality disorder and compared with the corresponding risk for these disorders in the first-degree relatives of patients with other non-schizophrenia-related personality disorders. The morbid risk for all schizophrenia-related disorders, and specifically for schizophrenia-related personality disorders, was significantly greater among the relatives of the probands with schizotypal and/or paranoid personality disorder than among the relatives of probands with other personality disorder. The morbid risk for other psychiatric disorders did not differ significantly between the first-degree relatives of the schizotypal/paranoid personality disorder and the other personality disorder control proband samples. These results suggest a specific familial association between schizophrenia-related disorders, particularly schizophrenia-related personality disorders, and clinically diagnosed schizotypal patients.

• The morbid risk of Alzheimer's disease was studied in first-degree relatives of 50 patients who met contemporary clinical research diagnostic criteria and 45 matched controls. Relatives of patients showed a 46% cumulative incidence of probable Alzheimer's disease by 86 years of age. The risk, which was four times the control value, is consistent with other recent reports using similar, modern methods. Although not conclusive, the data suggest the operation of a relatively common, dominant autosomal gene for Alzheimer's disease, the expression of which is delayed until late old age but is largely complete by 90 years of age.

IN REPLY.— Dr Heston has raised several interesting points regarding the methods and conclusions in our recent report concerning the morbid risk among first-degree relatives of patients with Alzheimer's disease. First, he suggests that the risk figures for first-degree relatives over 80 years of age are really not much greater than one would observe in the general population. He states that most population estimates run between 20% and 30% but cites no data. We are aware of no prospective studies indicating such high risks. Some studies indicate prevalence of all types of dementia as high as 22% after 80 years of age,1 but none of them suggests annual risks for Alzheimer's disease as high as the approximately 4% observed in first-degree relatives of Alzheimer's disease probands 80 to 86 years of age.Second, Dr Heston suggests that the risk among control relatives should be substracted from the risk among relatives