Clues revealed to cause of deadly kidney disease in newborns

(Press-News.org) Washington, DC -- Babies born with autosomal recessive polycystic kidney disease (ARPKD) often develop kidney failure because they have very large kidneys filled with tiny cysts. Even with excellent medical care, about 30% die shortly after birth. New research now provides clues into how gene defects may cause this condition, which occurs in 1 out of 20,000 newborns. The findings appear in an upcoming issue of the Journal of the American Society Nephrology (JASN), a publication of the American Society of Nephrology.

Mutations in a gene named PKHD1 cause ARPKD, but it's not clear how. Jason Bakeberg and Christopher Ward, ChB, PhD (Mayo Clinic) led a team that bred mice to have a small tag inserted into this gene. This tag allowed the researchers to follow the activities of the protein made by the gene, called fibrocystin.

"We found that small vesicles, termed exosome-like vesicles (ELVs), present in urine and other bodily fluids have abundant fibrocystin on their surface. This has allowed us to follow ELVs as they interact with primary cilia, or small hair-like structures that project into the urine from cells within the kidney's tubules," said Dr. Ward. "We believe that ELVs are involved in transporting a range of signals through urine and that ELV interactions with cilia are central to this signaling."

The findings may help investigators to understand how PKHD1 gene mutations cause ARPKD and to develop tests for the disease. "For example we are working on urine-based tests for polycystic kidney disease based on the use of ELVs," said Dr. Ward.

### Study co-authors include John Woollard, Marie Hogan, MD, PhD, Han-Fang Tuan, Ming Li, Jan van Deursen, PhD, Yanhong Wu, PhD, Bing Huang, PhD, Vicente Torres, MD, PhD, Peter Harris, PhD (Mayo Clinic); and Rachaneekorn Tammachote, PhD( Chulalongkorn University, in Thailand).

Disclosures: The authors reported no financial disclosures.

The article, entitled "Epitope-tagged Pkhd1 Tracks the Processing, Secretion, and Localization of Fibrocystin," will appear online at http://jasn.asnjournals.org/ on Monday, October 24, 2011, doi:10.1681/ASN.2010111173.

The content of this article does not reflect the views or opinions of The American Society of Nephrology (ASN). Responsibility for the information and views expressed therein lies entirely with the author(s). ASN does not offer medical advice. All content in ASN publications is for informational purposes only, and is not intended to cover all possible uses, directions, precautions, drug interactions, or adverse effects. This content should not be used during a medical emergency or for the diagnosis or treatment of any medical condition. Please consult your doctor or other qualified health care provider if you have any questions about a medical condition, or before taking any drug, changing your diet or commencing or discontinuing any course of treatment. Do not ignore or delay obtaining professional medical advice because of information accessed through ASN. Call 911 or your doctor for all medical emergencies.

Founded in 1966, and with more than 12,000 members, the American Society of Nephrology (ASN) leads the fight against kidney disease by educating health professionals, sharing new knowledge, advancing research, and advocating the highest quality care for patients.