Maccani and colleagues’ observations, however, were limited by a relatively small set of samples (n=25), as well as a lack of data regarding the duration of cigarette smoking during pregnancy, cigarette per day usage, or more extensive environmental exposure information (such as environmental pollutant exposure or secondhand/passive cigarette smoke exposure). Despite these limitations, their data comprise an important first step in determining associations between maternal cigarette smoking during pregnancy and aberrant miRNA expression in the placenta. Furthermore, more work is needed to investigate associations between maternal cigarette smoking during pregnancy and abnormal miRNA expression in a larger sample set with more complete environmental exposure information, as well as potentially using a hypothesis-generating approach, such as using miRNA microarrays (Maccani, et al., 2010; Maccani & Marsit, 2011). Future work assessing associations between exposure-influenced placental miRNA profiles and downstream neurobehavioral and developmental outcomes is also needed. For instance, longitudinal analyses across the lifespan will be critical for elucidating the impact of miRNA-mediated fetal programming on later health, behavior, and disease.
