To consider recent findings from quantitative genetic research
in the context of molecular genetic research, especially genome-
wide association studies. We focus on findings that go beyond
merely estimating heritability. We use learning abilities and
disabilities as examples. Recent twin research in the area of
learning abilities and disabilities was reviewed. Three findings
from quantitative genetic research stand out for their far-
reaching implications for child and adolescent psychiatry.
First, common disorders such as learning difficulties are the
quantitative extreme of the same genetic factors responsible for
genetic influence throughout the normal distribution (the Common
Disorders are Quantitative Traits Hypothesis). Second, the same
set of genes is largely responsible for genetic influence across
diverse learning and cognitive abilities and disabilities (the
Generalist Genes Hypothesis). Third, experiences are just as
influenced genetically as are behaviors and genetic factors
mediate associations be