Quantitative trait locus mapping: Fishing strategy or replicable results?

Genomewide scan, as shown by recently published linkage studies on the beha vior of mice or in psychiatry, provides evidence for replicated quantitativ e trait loci (QTL). Several studies of Alzheimer's disease have demonstrate d the promise of moving from clinical diagnoses to biological signs for psy chiatric investigations. Empirical studies also demonstrate that genetic ba ckground, differences in environment, epistatic effects, and definition of the phenotype (including psychiatric diagnosis) all actively contribute to limit the duplication of QTL.