Objectives: The receptor activator of nuclear factor-kappaB ligand (RANKL) is recognized as one of the important regulators of osteoclastogenesis. The expression of the tumour necrosis factor superfamily, member 11 (TNFSF11) gene, which encodes for RANKL protein, is increased relative to the expression of osteoprotegrin in cases of senile osteoporosis with hip bone fracture. Our aim was to find polymorphisms in the TNFSF11 gene promoter and to investigate their possible association with bone mineral density (BMD).
Methods: The TNFSF11 gene promoter region was screened for the presence of new sequence variations by direct sequencing. DNA sequencing revealed the presence of four sequence variations: -290C>T, -643C>T, -693G>C and -1594G>A. Association of the discovered polymorphisms with BMD was investigated in 115 Slovenian postmenopausal women, using restriction fragment length polymorphism analysis. After a year, bone loss in the association with the identified sequence variations was evaluated in 43 postmenopausal women.
Results: Three of the discovered sequence variations (-290C>T, -643C>T, -693G>C) proved to be polymorphic, whereas variation -1594G>A was only found in one patient. The frequencies of genotypes were as follows: CC (27.8%), CT (43.5%), TT (28.7%) for -290C>T polymorphism; CC (23.5%), CT (47.8%), TT (28.7%) for -643C>T polymorphism; and GG (22.6%), GC (51.3%), CC (26.1%) for -693G>C polymorphism. A statistically significant association of genotype with BMD at the femoral neck was observed only in the -290C>T polymorphism. Genotype CC was associated with lower BMD than the TT genotype (P = 0.022). In polymorphism -693G>C, a significant difference in bone loss rate was observed in total hip (P = 0.011) and femoral neck BMD (P = 0.037).
Conclusions: Four sequence variations were identified in the studied region of TNFSF11 gene promoter. Our results of preliminary clinical evaluation suggest that the -290C>T polymorphism in the TNFSF11 gene promoter could contribute to the genetic regulation of BMD.