*4.11. Statistical Analysis*

All statistical analyses were performed by using EXCEL 2019 (Microsoft, Redmond, WA, USA) with Statcel4 add-in software (OMS publishing, Saitama, Japan). The number of biological replicates (*n*) is described in the figure legends. In single pairs of quantitative data, after comparing the variances of a data set (using the *F*-test), an unpaired Student's *t*-test was performed. Statistical significance was defined in terms of *P* values less than 0.05 or 0.01.

**Author Contributions:** Conceptualization, Y.T., T.T., and B.S.; validation, Y.T., Y.K., and B.S.; formal analysis, Y.T.; investigation, Y.T., K.P., J.B., P.J., and Y.K. (i.e., Y.T. performed the experimental work using mammalian cells and analyzed the data; Y.K. supported the experimental work; K.P. and J.B. conducted sequencing analyses for clinical samples; P.J. was responsible for clinical observations; Y.T. performed statistical analyses); data curation, Y.T., T.T., and B.S.; writing—original draft preparation, Y.T., and B.S.; writing—review and editing, Y.T., T.T., and B.S.; supervision, H.S. and B.S.; project administration, B.S.; funding acquisition, Y.T., T.T., and B.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** The study was supported by the JSPS KAKENHI Grant, numbers 19K16441 (to Y.T.); 16H01808, 18KK0247, and 20H00568 (to T.T.). The study was also supported by grants from the Czech Republic Ministry of Health RVO 00023728 (Institute of Rheumatology), RVO VFN64165, and BBMRI-CZ LM2018125 (to B.S.); T.T. received research grants from "Gout and uric acid foundation of Japan"; "Takeda Science Foundation"; "Suzuken Memorial Foundation"; "Mochida Memorial Foundation for Medical and Pharmaceutical Research"; "The Pharmacological Research Foundation, Tokyo."

**Institutional Review Board Statement:** The studied proband and her family members were Czechs of Roma ethnicity diagnosed with familial (early-onset) hyperuricemia/gout. Written informed consent was obtained from each subject before enrollment in the study. All tests were performed in accordance with standards set by the institutional ethics committees, which approved the project (no. 6181/2015). All the procedures were performed in accordance with the Declaration of Helsinki.

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** Data supporting the findings of this study are included in this published article or are available from the corresponding author on reasonable request.

**Acknowledgments:** We would like to express our appreciation to all who took part in this study.

**Conflicts of Interest:** The authors declare no conflict of interest.
