Genotype and secondary hyperparathyroidism after renal transplantation

Polymorphic allelic variants of a great number of genes have been implicated in phenotypic modulation of different clinical conditions. Secondary hyperparathyroidism (SHP), a very common complication in uremic patients, is universally recognized to be caused by typically acquired factors (derangements in vitamin D, calcium and phosphate metabolism secondary to reduced renal function). However, a possible role of some polymorphisms has been suggested as a potentially additional causal factor in modulating the degree of clinical expression of SHP. Though the main causal factors of SHP are completely corrected by renal transplantation (RTx), a consistent proportion of RTx patients continue to have high PTH levels, this finding, too, has been suggested to be in part dependent on some genetic factors. Theoretically, polymorphisms of a great number of candidate genes might be involved at different steps in the phenotypic expression of SHP. However, VDR polymorphisms have been the object of more intense investigation. The results of the data in the literature are quite conflicting. Some studies suggest a role for BsmI polymorphism in affecting the degree of SHP and, to some extent, of bone demineralization, after RTx. At variance, other studies do not confirm these results. These discrepancies may be a result of the relatively low number of patients recruited in many of the above studies, on racial difference, on the degree of renal failure, based on the type of the studied polymorphism and on the presence of many other confounding factors. Furthermore, it cannot be excluded that the effect of the investigated genetic factors might be mediated by factors not directly linked to mineral metabolism. No definite conclusions can be drawn on the role, if any, of genetic factors in the phenotypic expression of SHP in RTx patients. In our opinion, there is no real justification at the present time for suggesting a widespread study of these genetic markers to predict the degree of SHP after renal transplantation.