Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (552 page)

   Usually asymptomatic, though patients with this condition have increased risk of renal abnormalities such as renal obstruction, infections, stones, and tumors. Laboratory abnormalities are usually due to these renal complications.

MEDULLARY CYSTIC KIDNEY DISEASE

   Medullary cystic kidney disease (MCKD), also known as autosomal dominant interstitial kidney disease (ADIKD), is inherited in an autosomal dominant pattern and characterized by progressive kidney disease and adult-onset renal failure. It is similar to juvenile nephronophthisis but occurs in older patients and is limited to the kidneys with no extrarenal organ involvement. Fluid-filled medullary cysts can be present in some cases.

   Three types of MCKD have been described based on the genetic mutations:

   Mutations in the
UMOD
gene, which encodes uromodulin (Tamm-Horsfall mucoprotein): this condition is also called MCKD type 2 or uromodulin-associated kidney disease (UAKD) and presents in the majority of MCKD cases. It is characterized by hyperuricemia that results from reduced urate excretion.

   Mutation in the
REN
gene, which encodes renin.

   Mutations in the
MUC1
gene, which encodes mucin 1 (also referred to as MCKD type 1).

   Mutations in
REN
and
MUC1
genes have been described in only some families. Additional mutations of other unidentified genes may account for some other cases.

   UAKD patients typically present during their teenage years with gout, hyperuricemia, and mild elevation in serum creatinine. ESRD typically develops between the ages of 20 and 70 years. Urinalysis is typically bland with minimal or no proteinuria.

   Similar to UAKD, patients with
REN
mutations also develop early-onset gout, but their CDK progresses more slowly and ESRD occurs after age 40. Additionally, these patients demonstrate anemia and may have hyperkalemia.

   Patients with
MUC1
mutations present with slowly progressive CKD with no early onset of gout.

   Diagnosis of all types is based on family history and clinical presentation. Definitive diagnosis is achieved by genetic testing.

Suggested Reading

Bleyer A. Autosomal dominant interstitial kidney disease (medullary cystic kidney disease). In: Basow DS (ed).
UpToDate
. Waltham, MA: UpToDate; 2013.

MEDULLARY SPONGE KIDNEY

   Definition