Second, “what about unaccounted heritability (h2)?” Heritability estimated from genome-wide single nucleotide polymorphism data (SNP-h2) depends on technical issues and especially sample size. The comparator is estimated from imprecise twin or family data (twin-h2 or pedigree-h2). “Unaccounted h2” refers to the difference between these estimates, and attempts to reconcile fundamentally different entities. Still, when the genomic study is sufficiently large (as with schizophrenia), SNP-h2 is around half of the pedigree-h2. A point often missed, however, is that explaining h2 is a minor goal. The main goals of the PGC are to gain biological, clinical, and therapeutic insights, which can arise regardless of the magnitude of heritability accounted for.
