accurately model the environment that human neurons reside in? 2) iPS cell technology is expensive and time consuming and for this reason some studies are limited to testing a single concentration of drug because of the increasing financial strain assaying many different concentrations would bring. 3) The effects of a drug or molecule may require additional factor(s) in order to fully produce a phenotype. Therefore, when interpreting iPS cell data from drug studies it is important to keep in mind that neural cultures produced from iPS cells may lack endogenous factors required to achieve an effect from a substance or molecule. 4) As with any in vitro study, patient-derived neural cells are not in their native environment. 5) Variations in in vitro culture conditions or even well-to-well variability may influence cellular phenotypes (i.e. gene expression patterns). Finally, 6) although the genetic sequence variations in neural cells made from alcohol dependent subjects are most likely preserved in the iPS cells, the somatic cells have a characteristic epigenetic profile that gives specific cell types a certain identity, i.e. heterogeneous. For example, skin fibroblasts collected from different parts of the body actually have different epigenetic landscapes represented by variations in transcriptomes.
