**8. Conclusions**

Various mutations and polymorphisms in the *ABCG2* gene diversely affect the structure, stability, trafficking, and function of this multifunctional transporter protein. Gaining insight into the cellular fate of different ABCG2 variants promotes establishing specific interventions to overcome the medical condition caused by either the wild type or the mutated forms of ABCG2. The classification of ABCG2 mutations proposed here is based on the cellular features of various defects; thus, the variants categorized into the same class require similar kinds of efforts to rescue the phenotype. A broad and well-established knowledge base is a prerequisite for prudent therapies; thus, our better understanding of the genetics, biochemistry, and cell biology of ABCG2 variants bearing various mutations could help to establish effective personalized treatments that consider the patients' genetic background.

**Funding:** This work has been supported by National Research, Development and Innovation Office, Hungary (grant numbers: OTKA\_K 128123 and FIEK\_16-1-2016-0005).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The author is grateful to Ágnes Enyedi, Balázs Sarkadi, and Tamás Heged ˝us for their advices and help in revising the manuscript. The author also thanks Rita Dóra Homolya for her contribution to the graphical design.

**Conflicts of Interest:** The author declares no conflict of interest.
