Finally, it’s possible that despite efforts to conceal study-group assignments, some patients became alert to their designated intervention, and those who still had pain and learned that they were in the control group may have elected to cross to the vertebroplasty group. Our study had many limitations. First, we allowed crossover at one month because both physicians and sufferers were reluctant to simply accept a longer period.Heat treatment of bovine serum albumin denatures the protein and results in reduced proteolysis24 in the relatively high pH of infants’ stomach in comparison with that of adults .25 Furthermore, the amount of intact bovine serum albumin entering the circulation is probably higher during infancy, before the gastrointestinal tract has matured and its own barrier function has been established.26,27 This amount could be increased during childhood gastroenteritis.28 Both the predominance of a cationic form and the increased amount of absorbed bovine serum albumin probably contribute to the advancement of membranous nephropathy in young children. Membranous nephropathy is characterized by a predominant Th2 immune response with production of IgG4 both in humans and in animals. IgG4 is exclusive among the IgG subclasses since it weakly activates complement and behaves mainly as a monovalent immunoglobulin.31-33 Therefore, IgG4 can develop small, nonprecipitating immune complexes that escape clearance and are hard to detect.