There have been many discussions about the most appropriate criteria for evaluating the validity of potential endophenotypic markers; some of these criteria are widely accepted, whereas others are more controversial.17, 85, 86 Other terms such as ‘intermediate phenotype' or ‘biological marker' are sometimes used interchangeably, whereas they differ in their meanings; endophenotypes include the idea that a heritable quantitative phenotype is closer in the chain of causality to the genes underlying the disease, but the latter terms do not necessarily reflect genetic underpinnings, and a minority of biological markers meet more than one or two endophenotype criteria.68, 87 Such criteria are important as they protect against the too casual use of non-valid endophenotypes, which would lead to invalid genetic studies and disappointments in psychiatric research.87
