Atacicept in Multiple Glomerular Diseases

Inclusion Criteria: * Weight of at least 40 kg * On a stable prescribed standard of care (SoC) treatment regimen according to local guidelines and the specific requirements for each disease * Systolic blood pressure ≤160 mmHg and diastolic blood pressure ≤90 mmHg at Screening. Diagnosis of IgAN, IgAVN, pMN, MCD, FSGS, or primary nephrotic syndrome For patients enrolling in IgAN cohorts (eligibility varies by cohort): * Age ≥ 18 years * Biopsy proven IgAN, IgAVN, or recurrent IgAN in kidney transplant * UPCR ≥ 0.5 g/g or UPE ≥ 0.5 g/day on 24h urine * eGFR≥ 20 mL/min/1.73m2 For patients enrolling in pediatric IgAN Cohorts (eligibility varies by cohort): * Age ≥ 2 years and \< 18 years * Biopsy proven IgAN or IgAVN * On stable prescribed regimen of RAASi (or SoC) for at least 8 weeks * UPCR ≥ 1.0 g/g or UPE ≥ 1.0 g/d on 24h urine * eGFR≥ 30 mL/min/1.73m2 For patients enrolling in pMN cohorts (eligibility varies by cohort): * Age ≥ 18 years * Biopsy-proven pMN * Anti PLA2R antibodies ≥ 25 RU/mL * UPCR ≥ 1.5 g/g or UPE ≥ 1.5 g/d on 24h urine * At low risk for spontaneous remission (based on severity or duration of disease) For patients enrolling in Nephrotic Syndrome cohorts (MCD, FSGS, or pediatric idiopathic nephrotic syndrome): * Age ≥ 10 years * eGFR ≥30 mL/min/1.73m2 * Adults with biopsy diagnosis of primary MCD or FSGS (adults) or children with challenging clinical course with steroids (frequenlty relapsing, steroid-dependent, or steroid-resistant) * UPCR ≥ 1.0 g/g or UPE ≥ 1.0 g/d on 24h urine * Evidence of anti-nephrin antibodies Key Exclusion Criteria: * Evidence of rapidly progressive glomerulonephritis (loss of ≥50% of eGFR) within 12 weeks prior to and at Screening) * Active viral or bacterial infections * Existing conditions or clinically significant laboratory abnormalities that may interfere with participation in this study * Administration of live and live-attenuated vaccinations within 30 days prior to enrollment * Immunosuppressant medications within 4 weeks prior to dosing with atacicept (except transplant maintenance immunosuppression). * Known hypersensitivity to atacicept or any component of the formulated atacicept * Additional criteria apply to each cohort/disease.