Safety and Pharmacokinetic Study of Subcutaneous ALXN1720 in Participants With Proteinuria

Inclusion Criteria: * Documented diagnosis of Lupus Nephritis, IgA Nephropathy, Primary Membranous Nephropathy, Focal Segmental Glomerulosclerosis, Diabetic Nephropathy, Hypertensive Nephrosclerosis, Minimal Change Disease, Thin Basement Membrane Nephropathy or Membranoproliferative Glomerulonephritis (all forms). Other cause of kidney disease may be included per investigator agreement with the Sponsor * Proteinuria \>=1 based on absolute amount in grams per day (g/d) as measured in one complete and valid 24-hour urine collection during Screening * Body weight ≥ 40 kg at Screening Exclusion Criteria: * Kidney transplant * Estimated glomerular filtration rate (eGFR) \< 30 mL/min/1.73 m2 during Screening * Known medical or psychological condition(s) or risk factor that, in the opinion of the Investigator, might interfere with the participant's full participation in the study, pose any additional risk for the participant, or confound the assessment of the participant or outcome of the study. * Treatment with complement inhibitors at any time. * Treatment with rituximab within 6 months before initiation of study drug on Day 1; or, planned treatment with rituximab within 3 months after initiation of study drug on Day 1. * Participation in another investigational drug or investigational device study within 30 days before initiation of study drug on Day 1 in this study or within 5 half-lives of that investigational product, whichever is greater.