psychological and medical traits [2]–[3]. This heterogeneity implies that distinct GVs may give rise to the same univariate trait score, and that the same GV may have different behavioral manifestations, depending on genetic background and environmental exposure. It also implies that phenotypes (e.g., symptoms, items, subtests) may be affected by different GVs. To appreciate this, consider diagnostic indicators of asthma, like spirometric measures, serum total IgE, and fractional exhaled nitric oxide. These measures are phenotypically correlated and all associated with asthma diagnosis, yet their genetic architecture may differ. When GWAS is subsequently conducted on asthma case-control status, however, both the plausible phenotypic and genetic heterogeneity of the trait is discarded. Likewise, depression symptoms like worrying, insomnia, and feeling lonely or irritable, and metabolic syndrome related measures like waist-to-hip ratio, fasting glucose levels, triglycerides, and high-density lipoprotein, are phenotypically correlated yet need not be subject to the same GVs. That is, while the conceptual multidimensionality of traits is often acknowledged in the phenotypic instruments – e.g. by including measures of multiple symptoms for disease traits, or multiple subtests to cover distinguishable dimensions of complex traits (e.g., spatial and verbal ability, memory, and general knowledge in cognition) - this phenotypic resolution is
