WINSTON-SALEM, N.C. – Researchers at Wake Forest University Baptist Medical Center and the University of Pittsburgh report in the current Journal of Medical Genetics that they have found defects in the gene that produces a common protein in urine and that these defects are linked to two inherited kidney diseases. For six years, the researchers had studied a family from Western North Carolina that has been plagued with a rare kidney disease, trying to learn more about the genetics of the disease.
Anthony J. Bleyer, M.D., associate professor of internal medicine (nephrology) at Wake Forest, said the gene ordinarily produces a protein called either uromodulin or Tamm-Horsfall protein. Uromodulin is the most common protein released into the urine, but its function is unclear.
Bleyer said that Thomas C. Hart, D.D.S., Ph.D. of the University of Pittsburgh and formerly of Wake Forest, had identified mutations in the gene leading to defects in the protein. Defects in this protein led to a disease called familial juvenile hyperuricemic nephropathy in the North Carolina family and two other families. It also appears responsible for a disease called medullary cystic kidney disease Type 2 in another family.
"There had previously been a report speculating that these two conditions were in fact variations of the same disease," said Bleyer. "Our research has been able to prove that they are."
"Finding the cause of the disease will allow family members to find out if they have the disease," he added. And before donating a kidney to a sibling, parent or child, family members can be tested to be sure they don''t harbor the disease.
The two diseases, which ultimately lead to irreversible kidney failure, are:
* Familial juvenile hyperuricemic nephropathy which produces gout at an early age.
* Medullary cystic kidney disease, which produces cysts in the middle of the kidney.
Bleyer said that doctors had known about the uromodulin protein for many years but they did not know its function. "The current study shows that uromodulin is likely important in reabsorbing water and salt in the kidney. It appears to act as a super-glue to prevent leaking in small tubes of the kidney." But how that leads to kidney failure isn''t clear and will now become a research focus. "Now, not only our group but all the world''s experts in uromodulin will turn their attention to this disease," said Bleyer. "We are hoping that this will lead to improved treatment."
The Wake Forest team made repeated trips to see the family, develop a family tree and obtain genetic samples from a number of family members. From this information, the team found distant family members who knew they suffered from kidney disease, but did not know the cause.
"It was a wonderful experience to get to know this family," said Bleyer. "Though affected by a severe disease, they were always happy and willing to participate in the studies that needed to be done to identify the gene. This was true of all four families with which we worked."
Through contacts with other institutions, Bleyer collected information on three other families, and passed the genetic data on to Hart for analysis. Hart first showed the linkage of the disease to chromosome 16, the affected chromosome, a year ago.
The gene was somewhere in an unexplored area of chromosome 16. "Even the people who have mapped the human genome had not provided a detailed map of this area," Hart said.
When Hart found the gene, he confirmed mutations in the gene first in the North Carolina family and then in the three other families.
"This study shows what we do best at Wake Forest," he said. "We were able to use all our research capabilities to tackle a problem that has plagued a family for more than five generations."
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