Kidney Week

Abstract: SA-PO628

Biallelic Variant in ENPP6 Alters Choline Metabolism in Humans and Conveys Loss of Enzymatic Function In Vitro

Session Information

• Genetic Kidney Diseases: Models, Mechanisms, and Therapies
  October 26, 2024 | Location: Exhibit Hall, Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: Genetic Diseases of the Kidneys

• 1202 Genetic Diseases of the Kidneys: Non-Cystic

Authors

• Mertens, Nils David, Boston Children's Hospital, Boston, Massachusetts, United States

Nils David Mertens, MD

• Kano, Kuniyuki, Tokyo Daigaku Daigakuin Yakugakukei Kenkyuka Yakugakubu, Bunkyo-ku, Tokyo, Japan

Kuniyuki Kano, PhD

• Franken, Gijs AC, Boston Children's Hospital, Boston, Massachusetts, United States

Gijs AC Franken, MS, MSc, PhD

• El Desoky, Sherif Mohamed, King Abdulaziz University Hospital, Jeddah, Saudi Arabia

Sherif Mohamed El Desoky, MD

• Kari, Jameela Abdulaziz, King Abdulaziz University Hospital, Jeddah, Saudi Arabia

Jameela Abdulaziz Kari, MD, PhD

• Shril, Shirlee, Boston Children's Hospital, Boston, Massachusetts, United States

Shirlee Shril

• Hildebrandt, Friedhelm, Boston Children's Hospital, Boston, Massachusetts, United States

Friedhelm Hildebrandt, MD

Background

Congenital Anomalies of the Kidneys and Urinary Tract (CAKUT) are the leading cause of chronic kidney disease before 25 years of age. In previous studies, we have proposed ENPP6, encoding a membrane-bound choline-specific phosphodiesterase, as a potential novel candidate gene for monogenic CAKUT.

Methods

Segregation analysis of a potentially pathogenic ENPP6 variant (c.727A>G; p.M243V) was performed via exome sequencing in a family with CAKUT and correlated with choline metabolites in urine samples measured via mass spectrometry. A fluorescent probe cell assay was established to quantify the enzymatic activity of full-length human wildtype and mutant ENPP6.

Results

In parents and four brothers, we detected a potentially pathogenic homozygous ENPP6 variant (c.727A>G; p.M243V) in a boy with posterior urethral valves and neurogenic bladder. Both parents and two brothers are unaffected heterozygous carriers. One brother is biallelic wildtype. We collected urine samples from the whole family and detected the phosphocholine metabolite beta-GPC exclusively in the urine of the affected boy. These findings are consistent with urine analysis on published Enpp6 knockout mice. Next, we demonstrated that wildtype full-length human ENPP6 transiently overexpressed in HEK293 cells catalyzes the release of strongly fluorescent 2-Me-4OMe TG from a non-fluorescent synthetic probe (TG-mPC) consisting of the ENPP6 substrate phosphocholine linked to the fluorophore Tokyo green in a time and concentration-depended manner. Mutated ENPP6^M243V had reduced release of fluorescent 2-Me-4OMe TG compared to wildtype ENPP6.

Conclusion

This study provides functional evidence that biallelic variants in ENPP6 can cause human CAKUT.

Funding

• NIDDK Support