Any of a large group of diseases that affect the glomerulus of the kidneys. They may be classified by clinical severity, by histological changes in the kidney, or by etiology. Etiological factors include primary glomerular disease; disease secondary to systemic disease, such as lupus erythematosus or polyarteritis; infectious disease such as streptococcal infection, malaria, syphilis, or schistosomiasis; metabolic disease such as diabetes or amyloidosis; toxins such as mercury, gold, or snake venom; serum sickness; and drug hypersensitivity.