Linda - sometimes it can be genetic, but I think that's more breed specific. In most cases, PLN is caused by an underlying disease. In my foster Tucker's case, his PLN was either caused by his Erlichia or his pancreatitis - we can't be sure which
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The key to best prognosis is early diagnosis of PLN and identifying underlying cause and treating it in time.
And from that article - some other causes:
Diseases associated with glomerulonephritis in the dog include infectious diseases (heartworm disease, Ehrlichiosis, Lyme disease, Rocky Mountain Spotted Fever [RMSF], pyometra, chronic bacterial infections, bacterial endocarditis, septicemia, Brucellosis, Leishmaniasis, Trypanosoma, and infectious canine hepatitis), neoplasia, inflammatory diseases (pancreatitis, systemic lupus erythematosus [SLE], polyarthritis, chronic skin disease, and prostatitis), and other conditions (Cushing's disease, diabetes mellitus). In cats, GN can be associated with feline leukemia virus, feline infectious peritonitis, mycoplasmal polyarthritis, neoplasia, pancreatitis, SLE, other immune diseases, and diabetes mellitus. In many cases, an underlying cause cannot be discovered, and these are classified as idiopathic. Amyloidosis can be a familial disorder in Shar Pei dogs and Abbysinian cats, and it can also occur in conjunction with chronic antigenic stimulation (i.e. chronic pyoderma, neoplasia). Breeds with a high incidence of familial glomerulopathy include Soft-coated Wheaton Terriers and English cocker spaniels.
Familial PLN has been reported in many other breeds.