TGFb1 was suspected as a factor for renal fibrogenesis in BEN since the interstitial fibrosis is the major feature of disease [9]. In the present study we assessed whether the polymorphism Thr263Ile in TGFb1 was associated with BEN. The established allele frequencies differed signifi­cantly (p = 0.047) between groups. We found a higher prevalence of the wild type allele 263Thr in BEN patients compared to the controls (0.98 versus 0.93), while the variant allele 263Ile had a lower frequency (0.02 versus 0.07).

Allele 263Ile was prevalent in the studied individuals of Bulgarian origin as compared to the data on Cauca­sians, but the differences were not significant in a view of the total number of studied individuals (p = 0.27, c2 = 1.192) [6].

The lower frequency of the variant allele in BEN cases could not be explained, due to the lack of data on the effect of this polymorphism to gene product activity. It was supposed that allele 263Ile inhibits protein activity by influence on the cleavage of the active protein from the latent protein [6]. If such genotype-phenotype association exists, the established lower frequency of the variant allele 263Ile in BEN may serve as an indicator that active TGFb1 protein is more frequent in BEN patients than in the Bulgarian population.

A similar association between the active TGFb1 pro­tein and patients with lung fibrosis was found, where the wild type allele 25Arg was significantly more frequent in patients than in controls [4,5]. The variant allele 25Pro was significantly less frequent.

The results of the present study warrants further inves­tigation and full allelic assignment for polymorphism at codons 25 and 10 of the TGFb1 gene. Another four poly­morphisms, at positions –988, –800, –509 and 72, could also have effect in BEN. Their location is not in the con­sensus sequences as Thr263Ile, but this does not exclude the possibility for their modulation effect on TGFb1 ex­pression [6]. The remaining TGFb1 polymorphisms, re­lated to modulation of gene expression, may contribute to the development of fibroses in BEN kidneys. A further aspect for evaluating the role of TGFb1 for BEN is inves­tigation of the TGFb1 local production in renal cells of BEN kidneys.