Type 2 MCKD (also known as familial juvenile hyperuricemic nephropathy) reflects mutations in the UMOD gene, located on chromosome 16p12. This gene encodes uromodulin, also known as Tamm-Horsfall mucoprotein, which is produced in the thick ascending limb (TAL). The mutations causing type 2 MCKD interfere with the export of uromodulin from the tubular epithelial cells into the tubular lumen. The accumulation of abnormal uromodulin results in cell death and tubular atrophy. An increase in proximal salt reabsorption is typically enough to offset the salt wasting that would otherwise result from TAL dysfunction. Patients develop progressive renal insufficiency, however, that typically becomes apparent during the second decade. For uncertain reasons, patients also develop hyperuricemia, generally before the onset of renal dysfunction, that leads to recurrent episodes of gout. The combination of renal insufficiency, gout, and a family history of both should raise suspicion of the diagnosis of type 2 MCKD, which is established with genetic testing. Although treatment is mostly supportive, patients benefit from allopurinol, which reduces the incidence of gout attacks and, in some studies, has been shown to slow the progression to ESRD.