It is well established that genetic factors play a major role in the pathogenesis of osteoporosis. Previous reports have suggested that vitamin D receptor (VDR) gene polymorphisms, particularly the BB, tt and AA genotypes, are associated with low bone mineral density (BMD). If these VDR genotypes are indeed an important determinant of BMD, then a population of related osteoporotic individuals (mother-daughter or sister-sister relationship) should have a high prevalence of the BB, tt or AA VDR genotypes. To test this hypothesis we determined the VDR genotypes in 26 osteoporotic persons (age 44.3 +/- 12.7 years, mean +/- SD) belonging to 12 families. Furthermore, for comparison with existing studies, we applied the VDR genotype analysis in a population of 53 unrelated healthy subjects (age 45.2 +/- 9.8 years, mean +/- SD) and 59 unrelated osteoporotic subjects (age 52.1 +/- 9.0 years, mean +/- SD). The menopausal status of the healthy and osteoporotic populations was pre-, peri- and mostly early postmenopausal. The proportions of the three genotypes, BB, tt and AA, within the 12 osteoporotic families were 15%, 12% and 27%, respectively, whereas the proportions of the other three homozygous genotypes (bb, TT, aa) were 50%, 50% and 23%. The distribution of the BB, tt and AA genotypes in the normal population was 21%, 21% and 36%, respectively (vs bb, TT, aa: 36%, 38%, 21%), whereas in the osteoporotic population it was 24%, 20% and 34% (vs bb, TT, aa: 27%, 34%, 14%). Our data indicate that there is not a statistically significant (p>0.05) difference in the VDR genotype frequencies within osteoporotic families as compared with the same genotypes in the population of unrelated normal or osteoporotic subjects. VDR genotype analysis showed no significant relation between VDR polymorphisms and BMD or Z-score values at the lumbar spine. This study demonstrates the lack of a heritability pattern between the BB, tt and AA genotypes and low BMD.

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The effect of oestrogens on oestrogen-receptive organs and cells is mediated via intracellular receptors (ERalpha and ERbeta). Oestrogen receptor gene polymorphisms in the region encoding the N-terminal portion of the protein are reportedly associated with pathological conditions including breast cancer, hypertension, spontaneous abortion and coronary heart disease. A silent mutation in codon 10 of exon 1, detected in ER-negative and ER-positive human breast cancer cell lines, in breast tumors and blood DNA from breast cancer patients, has been recognized as a polymorphic site. In this study we examined, by denaturing gradient-gel electrophoresis and DNA sequence analysis, the possible presence of a codon 10 polymorphic site in normal oestrogen target organs and cells such as the uterus (myometrium and endometrium), in the placenta and peripheral blood mononuclear cells and in a benign uterus tumour (leiomyoma). We have detected ER codon 10 polymorphism in these samples and have compared them to those observed in breast cancer samples. All tissues and cells studied were homozygous for the wild-type gene, and were heterozygous as well as homozygous for the codon-10-variant type. These results indicate that the presence of the codon-10-variant type is not a characteristic of breast cancer. Out current findings suggest that further investigations are warranted to elucidate the possible linkage of ER codon 10 polymorphism to physiological and pathological conditions.

Estrogens are important determinants of bone mineral density (BMD) mediating their effects via estrogen receptor alpha (ERalpha) and beta (ERbeta). The strong genetic predisposition to osteoporosis, and the fact that alterations in the aminoterminal region of ERalpha have been linked to bone disturbances, prompted us to identify genetic alterations in exon 1 and exon 2 of ERalpha in osteoporotic individuals. Sixty-two unrelated normal subjects (age 46.1+/-9.5 years) and 72 unrelated osteoporotic subjects (age 52.3+/-7.9 years) were studied. Their menopausal status was pre- and perimenopausal. We also included 30 related osteoporotic individuals (mother-daughter or sister-sister relationship) (age 46.2+/-12.8 years) belonging to 14 families who where also pre- and perimenopausal. DNA was extracted from peripheral blood, exons 1 and 2 were amplified by polymerase chain reaction (PCR) and were further submitted to denaturing gradient gel electrophoresis (DGGE), single stranded conformational polymorphism (SSCP), restriction fragment length polymorphism (RFLP) and sequence analysis. Bone turnover markers were also determined. Two polymorphisms were identified in exon 1 (codons 10 and 87) in both normal and osteoporotic women. Statistical analysis revealed no difference (P>0.05) in the ERalpha genotype frequencies within osteoporotic families as compared with the same genotypes in the unrelated normal or osteoporotic subjects. Codon 10, codon 87 polymorphisms were not related to BMD or bone turnover markers. No other mutations were found in exons 1 and 2 in all subjects studied. Genetic alterations in exons 1 and 2 of ERalpha are not associated to osteoporosis and familial osteoporosis. Moreover, the codon 10 and codon 87 polymorphisms do not seem to be correlated with BMD and bone turnover markers.