Second, the challenge of generalizability persists, and may, in fact, be more acute in the setting of monozygotic twin studies. Generalizability is especially challenged in studies that consider the etiology of psychopathology, as it is plausible that this population may face stressors and protective factors particular to monozygotic twins—these include, for example, differences in neonatal brain structure between twins and singletons.[64]
