Nephrotic syndrome is a kidney disorder characterized by excessive protein loss in the urine, leading to low protein levels in the blood. This condition often results in swelling, particularly in the legs and around the eyes, due to fluid retention. The syndrome can be caused by various underlying conditions, such as diabetes or lupus, and may affect people of all ages. Diagnosis typically involves urine tests, blood tests, and sometimes a kidney biopsy to determine the cause and guide treatment options.