Supplementary Material for: Successful Living Kidney Donation from Heterozygous Carrier Parents to Siblings with Coenzyme Q8B Nephropathy: Two Case Series

Introduction:
Coenzyme Q8B (COQ8B) nephropathy is an autosomal recessive hereditary disorder caused by primary coenzyme Q10 (CoQ10) deficiency. It manifests as a genetic steroid-resistant nephrotic syndrome (SRNS), typically of childhood-onset. CoQ10 supplementation is a treatment option; however, it is not always effective in an entire patient population, leading to end-stage kidney disease. Kidney transplantation (KTx) is an effective treatment option for genetic SRNS; however, living KTx within biologically related members is associated with increased risk of allograft failure in recipients and future kidney dysfunction in donors. Here, we present two successful cases of living kidney donations from heterozygous carrier parents to their siblings with COQ8B nephropathy.

Case presentation:
The family comprised two parents and three siblings. Two of the daughters were diagnosed with proteinuria at 11 and 8 years of age, respectively. COQ8B nephropathy diagnosis was confirmed by next-generation and Sanger sequencing analysis, which revealed a novel compound heterozygous mutation in the COQ8B gene (c.737G>A and c.1468C>T). An older sister missed an opportunity for CoQ10 supplementation due to late diagnosis, whereas a younger sister did not respond to CoQ10 supplementation. Living kidney donation from father to the older sister and from mother to the younger sister was successfully performed without posttransplant recurrence in recipients or kidney dysfunction in donors within 5 and 2 years of follow-up.

Conclusion:
Parent-to-child KTx may be an effective treatment option within family members affected with COQ8B nephropathy.