INCLUSION CRITERIA

Renal biopsy showing FSGS, including all variants with the exception of HIV-associated FSGS.

Nephrotic range proteinuria, defined as 24 hour urine protein excretion greater than or equal to 3.5 g/d in adults and children weighing greater than or equal to 70 kg and greater than or equal to 50 mg/kg in adults or children weighing less than 70 kg. Proteinuria will be assessed with at least three 24 hour urine collections obtained during the baseline period (for these collections, there is no minimum period, the maximum period is 3 months prior to study entry, and the most recent must be within 1 month of entry). These measurements will be obtained while on angiotensin antagonist therapy (if tolerant of this medication) and will exclude urine collections judged inadequate based on creatinine appearance. For patients in the drug overlap group, baseline proteinuria will be determined from patient's records demonstrating on at least one urine collection, proteinuria greater than 3.5 g/d while off immunosuppressive therapy.

Ability and willingness to provide informed consent (adults greater than or equal to 18.0 years) or assent (children greater than or equal to 13.0 years).

Completion of a therapeutic trial of at least one of the following, without sustained CR:

Steroid therapy for greater than or equal to 8 weeks, either daily or alternate day or intermittent (oral or parenteral)

Cyclosporine or tacrolimus or mycophenolate mofetil for greater than or equal to 3 months

Cyclophosphamide (either oral or intravenous) or chlorambucil for greater than or equal to three months

EXCLUSION CRITERIA

Intolerance to sirolimus or prior use of sirolimus for FSGS.

Estimated GFR less than 30 mL/min/1.73m(2). The rational is that 1) sirolimus therapy is most likely to be beneficial during the early phase of FSGS, before progressive fibrosis in the glomeruli and interstitium has become the dominant abnormality and may be irreversible, and 2) we wish to enroll patients who are unlikely to progress to ESRD within the one year treatment period.

Patients following renal transplant. We wish to rest sirolimus with a minimum of other immunosuppressive therapy.

Children less than 13.0 years.

Uncontrolled hypertension, defined as BP greater than 140/90 on greater than 25% of measurements.

Pregnancy, lactation, or unwillingness or inability to practice effective contraception. The rationale is that the safety of sirolimus in pregnancy has not been determined and excretion via breast milk may alter pharmacokinetics.

Chronic active infections requiring treatment, including untreated reactive PPD, or any infection sufficiently severe require parenteral antibiotics during the preceding 30 days. The rationale is that immunosuppression may exacerbate infection.

HIV-1 infection or hepatitis B infection or hepatitis C infection (defined as detectable RNA off anti-viral therapy). The rationale is that immunosuppression may exacerbate infection.

Chronic liver disease sufficiently severe to impair sirolimus metabolism; this would include prolonged pro-thrombin time.

Basal thrombocytopenia less than 100,000 cells/microliter or absolute neutrophil count less than 2000 cells/microliter or hematocrit less than 30. The rationale is that sirolimus may further lower cell counts.

Cancer diagnosis or cancer recurrence within the preceding 5 years, excluding basal cell carcinoma of the skin. The rationale is that cancer progression may be accelerated by immunosuppression.