Literature data indicate that as a result of achievements in medical genetics, the pathogenesis of the development of hormone-resistant isolated and syndromal nephrotic syndrome in pediatric and adult patients has been established. Clinical and genetic features of hereditary isolated or syndromal nephrotic syndrome in pediatric and adult patients are caused by mutations of genes encoding the main components of the glomerular basal membrane, slit diaphragm, structural and functional proteins of the podocyte. Clinical manifestations of hereditary nephrotic syndrome in pediatric and adult patients aged 0 to 70 years, progression to terminal renal failure from 5 months to 75–80 years, depending on genetic and clinical and morphological features, are established. Molecular Genetic testing in steroid-resistant isolated and syndromal nephrotic syndrome conducted before the start of cytostatic therapy and kidney biopsy in pediatric and adult patients is of important clinical significance for making decisions about the feasibility of kidney biopsy and immunosuppressive therapy evaluating the rate of progression to terminal renal failure, and choosing immunosuppressive therapy before kidney transplantation. The problem of early diagnosis of hereditary isolated and syndromal nephrotic syndrome in paediatric and adult patients facing domestic nephrology should be solved by the introduction of molecular genetic testing in nephrological practice.