In the renal sinus, there are 7 to 8 funnel-shaped calyces that encircle the renal papillae, 2 to 3 calyces that form a large calyx, and 2 to 3 large calyces that converge 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. Blunted renal calyces are one of the clinical manifestations of nail-patellar syndrome, as well as one of the complications of nail-patellar syndrome. The syndrome is autosomal dominant and the locus is linked to the loci for adenylate cyclase and ABO blood group located on chromosome 9. Pathogenesis: Little is known about the pathogenesis of this syndrome, which has been suggested to be a collagen disease with abnormalities in the synthesis, assembly or degradation of collagen. The cytologic mechanisms of this disease have not been investigated. The lack of non-glomerular basement membrane damage in pathological changes suggests that the various damages in this syndrome may originate from different mechanisms and that not all damages are 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 of kidney biopsies from 2/3 of patients do not bind to this monoclonal antibody, suggesting some degree of heterogeneity in the basement membrane fraction of this syndrome 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 in this syndrome.