Frasier syndrome (FS) is a rare disease characterized by male pseudohermaphroditism and slowly progressing nephropathy. FS originates from heterozygous mutation in the intron 9 splicing donor site of Wilms' tumor suppressor gene (WT1). Focal segmental glomerular sclerosis is common in FS, but there have not been so many detailed pathologic investigations. The authors examined the kidneys of 3 patients with FS. The results showed that nephropathy started as mesangial proliferative glomerulonephritis, and later a concomitant focal segmental lesion developed. In all cases, electron microscopy results showed widespread thinning, splitting, and lamellation of the glomerular basement membrane, which mimicked hereditary nephritis. Throughout adulthood, WT1 protein expresses on glomerular podocytes. Recent reports described that podocytes expressing WT1 play an important role in maintaining the glomerular basement membrane. Hereditary nephritis-like glomerular basement membrane findings in FS suggest that one of the important functions of podocytes is to form and maintain the glomerular basement membrane.
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