Second, developmental state: neurons differentiated from iPSCs most closely resemble cells of the fetal brain, a problem for modeling diseases that emerge later in life.97 This topic is the subject of active research aiming at developing techniques to mimic cellular maturation and aging.98 Third, current protocols for generating iPSCs vary in efficiency and produce heterogeneous populations.25 This could be due to the fact that iPSCs accumulate mutations in culture over time.99 Although transdifferentiation techniques skip potentially crucial phases of neuronal development, these techniques offer a potential solution for this problem.100 Fourth, current techniques for differentiating iPSCs yield a heterogeneous population of neuronal subtypes, which may have varying roles in disease pathogenesis.101 Future protocols differentiating iPSC into more precisely defined neural subtypes may reveal phenotypes that are hidden using current protocols. Fifth, the expensive and time-consuming nature of generating iPSCs and differentiating them into neurons often leads to small sample sizes for most reported studies. Currently, scaling up the experiments to include more subjects remains a major obstacle. However, new techniques are being developed to reduce the time and costs required
