Some cases of Alzheimer's disease are inherited as an autosomal dominant trait. Genetic linkage studies have mapped a locus (AD3) associated with susceptibility to a very aggressive form of Alzheimer's disease to chromosome 14q24.3. We have defined a minimal cosegregating region containing the AD3 gene, and isolated at least 19 different transcripts encoded within this region. One of these transcripts (S182) corresponds to a novel gene whose product is predicted to contain multiple transmembrane domains and resembles an integral membrane protein. Five different missense mutations have been found that cosegregate with early-onset familial Alzheimer's disease. Because these changes occurred in conserved domains of this gene, and are not present in normal controls, they are likely to be causative of AD3.

Alzheimer's disease is a leading cause of morbidity and mortality among the elderly. Several families have been described in which Alzheimer's disease is caused by an autosomal dominant gene defect. The chromosomal location of this defective gene has been discovered by using genetic linkage to DNA markers on chromosome 21. The localization on chromosome 21 provides an explanation for the occurrence of Alzheimer's disease-like pathology in Down syndrome. Isolation and characterization of the gene at this locus may yield new insights into the nature of the defect causing familial Alzheimer's disease and possibly, into the etiology of all forms of Alzheimer's disease.

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SUMMARY For circulating norepinephrine (NE) to reflect sympathetic activity validly, plasma NE should show an intensity-dependent increase during sympathetic stimulation and decrease during sympathetic inhibition, and circulating NE should correlate with more directly obtained measures of sympathetic activity. Review of published evidence indicates that NE in peripheral plasma satisfies these criteria. However, models used to explain the relationship between circulating NE and sympathetic activity must take into account processes intervening between the synaptic cleft and free NE in the circulation and, since sympathetic outflow is regionalized, the contributions of specific vascular beds to circulating NE. In this report a model is presented where removal processes for NE are viewed as acting in series to produce a gradient in NE concentrations from synapse to plasma, and where the relative contributions of specific vascular beds are calculated from the arteriovenous difference in plasma NE across those beds and the percentage of cardiac output distributed to them. In general, venous plasma NE provides a useful estimation of average sympathetic outflow. (Hypertension 5: 552-559, 1983) KEY WORDS • norepinephrine • epinephrine • catecholamines • sympathetic nervous system • hypertension • spontaneously hypertensive rat M ANY recent studies have used venous plasma norepinephrine (NE) concentrations as an index of sympathetic neural activity in humans, and several of these studies have reported plasma NE to be increased in some patients -in particular, young patients -with essential hypertension.1 -2 In general, these studies have not critically evaluated the relationship between sympathetic outflow and circulating NE. An understanding of the factors determining that relationship is crucial for interpreting NE levels in terms of sympathetic neural activity in disease states such as essential hypertension. In this report we discuss the validity of antecubital venous plasma NE for clinical evaluation of sympathetic function, taking into account the factors known to intervene between sympathetically mediated NE release and levels of NE in venous plasma.For circulating NE to be a valid reflection of sympathetic activity, several criteria must be met: 1) during stimulation of sympathetic outflow, plasma NE should From the National Heart, Lung, and Blood Institute (Dr. Goldstein); the Laboratory of Clinical Science, National Institute of Mental Health (Drs. Polinsky and Kopin), National Institutes of Health, Bethesda, Maryland; and the Department of Psychology, University of Virginia, Charlottesville, Virginia (Dr. McCarty).Address for reprints: National Heart, Lung, and Blood Institute, NIH, Building 10 8C116, Bethesda, Maryland 20205. Received November 17, 1982; revision accepted January 25, 1983. increase in proportion to the intensity of stimulation; 2) during inhibition of sympathetic outflow, plasma NE should decrease, with the extent of decrease similarly related to the extent of inhibition; and 3) plasma ...