| References | Targeted Gene | Consequences | Advantages | Disadvantages | Ethics and the use of CRISPR/Cas9 in gene therapy |
| Park et al., 2019 [27] | BACE1 | Cas9-Bace1 nanocomplex treatment of these App knock-in mice decreased the number of Bace1+ cells, reduced Aβ42 secretion, and improved cognitive deficits compared to controls. Taken together, the data indicate that targeting Bace1 by the Cas9 nanocomplex ameliorates Aβ-associated pathologies and cognitive deficits in 5XFAD and App knock-in mouse models of Alzheimer’s disease. | Both Cas9 protein and sgRNA are carried on the same vector; ensures that both are expressed in the same cell. This system offers improved stability, especially during handling and manufacturing, compared to the other two strategies. | However, despite these positive results, challenges remain in translating such an approach to a clinical setting. Cas9 delivery cannot target widespread dysfunction in neural circuits; thus, is not likely to prevent disease progression in Alzheimer’s disease patients. I | Genome editing techniques used in gene therapy can sometimes be imprecise and uncontrollable, which can lead to unexpected and unpredictable effects. These genetic errors, including “on-target” and “off-target” effects, can lead to unanticipated results during genome editing [42] .
CRISPR can also induce double-stranded breaks (DSBs) in the target DNA and by genetic breaks, it can trigger apoptosis rather than the planned genetic modification [42] .
In the application of gene therapy using viral vectors, we must apply not only the principle of ethical precaution but also the fundamental bioethical principles of beneficence and non-maleficence. |
| Offen et al., 2018 [37] | APOE ε4 | Application of the apoE4 targeted system led to a significant decrease of ApoE4 protein levels (−56%) without any significant changes in ApoE3 levels. | Specific elimination of the ApoE4 allele using a CRISPR Cas9 variant without harming ApoE3. | There are no clinical trials on humans yet Potential for the random insertion of plasmid fragments into the gene. | |
| Sun et al., 2019 [23] | APP | Attenuating β-cleavage and Aβ production | CRISPR/Cas9 editing of APP C-terminus attenuates β-cleavage and promotes α-cleavage | Although the strategy of Sun et al., 2019 have reciprocal effects on β/α-cleavage in various cells, they did not test the tools in an AD mouse model. Furthermore, their current off-target analyses cannot detect very small DSBs. No deleterious effects were seen in neurophysiologic parameters, though our experiments were in cultured neurons and in vivo effects are unknown. | |
| Moreno et al., 2018 [43] | PSEN2 | Chronic insulin administration reduces the Aβ42/40 ratio in the conditioned media of BFCNs harboring FAD mutations Unbiased exploratory analyses revealed that some subtle memory benefits resulted and that the memory changes were associated with changes in Aβ42 | The discovery of insulin’s ability to correct calcium flux and lower the Aβ42/40 ratio suggests that insulin acts to oppose the pathophysiology of AD. | Potential for the random insertion of plasmid fragments into the gene. One of the advantages of CRISPR/Cas9 gene editing is that it is somatic rather than germline. Thus, the gene editing results will manifest only in the treated individual and will not be passed to future generations Instability of RNA |