In the renal sinus, 7-8 funnel-shaped calyces encircle the renal papillae, and 2-3 calyces form a large calyx. 2-3 calyces merge to form a flattened, funnel-shaped renal pelvis. Blunting of the calyces refers to the blunting of the anterior and posterior flattened, funnel-shaped shape of the calyces as a result of some organic condition. The pathogenesis of blunted calyces is poorly understood and is thought to be a collagen disease with abnormalities in the synthesis, assembly, or degradation of collagen. The cytologic mechanism of this disease has not been investigated. The lack of non-glomerular basement membrane damage in the pathological changes suggests that the damage may originate from different mechanisms and that not all damage is associated with basement membrane abnormalities. The development of anti-glomerular basement membrane nephritis in a small number of patients supports the hypothesis that the glomerular basement membrane component is abnormal. Studies using monoclonal antibodies against the Goodpasture epitope have found that glomerular basement membranes from kidney biopsies from 2/3 of patients do not bind to the monoclonal antibody, suggesting some degree of heterogeneity in the basement membrane fraction, and also suggesting the presence of Goodpasture antigen deficiency or alteration. It is worth pointing out that it is not clear whether this is a primary or secondary alteration. The main clinical manifestations of renal damage are proteinuria, microscopic hematuria edema and hypertension, occasionally nephrotic syndrome, with a relatively benign course, with only 10% of patients entering renal failure at an advanced stage. Extra-renal manifestations include dystrophy of the nails, patellar agenesis on one or both sides, elbow deformities, angular pelvis and other skeletal abnormalities. Nail-patellar syndrome is most often noted for difficulty walking due to patellar agenesis and can be diagnosed on the basis of typical skeletal changes, with the presence of renal impairment being more likely to confirm the diagnosis.