In their study of monozygotic twin pairs in the Add Health sample, the associations of sleep duration with several outcomes including suicidal ideation, delinquency, and drug use were reduced to non-significance when genetic and shared environmental factors were accounted for in the model. (link.springer.com)
It examines a large sample of monozygotic twins in Denmark to see if their cultural activity was related to their teacher - given GPA, exam - based GPA, and rate of completing secondary school. (educationnext.org)
Of course, the approach won't work with monozygotic twins, whose genes are identical. (discovermagazine.com)