The genetics of osteoporosis

The effect of vitamin D receptor BsmI genotype on the response to osteoporosis treatment in postmenopausal women: a pilot study

AIM

The purpose of our study was to investigate the possible effect of BsmI vitamin D receptor (VDR's) polymorphism on changes in bone mineral density (BMD) and bone turnover markers in postmenopausal women receiving different treatments.

MATERIAL AND METHODS

This pilot study included 42 postmenopausal women with elevated fracture risk, randomized into 1-year treatment with weekly oral alendronate or daily subcutaneous teriparatide. Both groups received daily supplements of 1000 mg calcium and 800 IU vitamin D. Blood samples were obtained for biochemical evaluation and genotyping. BMD at the lumbar spine and femoral neck were assessed with dual energy X-ray absorptiometry. Baseline, follow-up BMD and markers of bone turnover were assessed according to the BsmI genotype.

RESULTS

BMD at the lumbar spine increased in patients carrying at least one b allele, while it decreased in patients with the BB genotype (P = 0.041). Whereas no gene-treatment interaction was observed in teriparatide-receiving patients, women with the BB genotype receiving alendronate resulted in negative BMD (-0.056 ± 0.032 g/m(2) ) and T-score (-0.295 ± 0.190) gradient, compared to carriers of the b allele (BMD: +0.020 ± 0.017 g/m(2) , P = 0.054; T-score: +0.217 ± 0.100, P = 0.030). No effect of genotype was apparent with respect to gradients of biochemical bone markers.

CONCLUSIONS

These preliminary results indicate that alendronate has a differential effect on BMD, depending on the VDR genotype. Carriers of the b allele may be more responsive to treatment compared to patients with the BB genotype. The interaction of VDR's BsmI polymorphism with the efficacy of the anti-osteoporotic treatment needs further investigation by larger prospective studies.

Hip fracture risk and different gene polymorphisms in the Turkish population

BACKGROUND

We aimed to discuss the risk assessments for both patients with hip fractures due to fall-related, low energy traumas and non-fractured control patients by examining bone mineral density and genetic data, two features associated with femoral strength and hip fracture risk.

METHODS

Twenty-one osteoporotic patients with proximal femur fractures and non-fractured, osteoporotic, age- and gender-matched controls were included in the study. Bone mineral density measurements were performed with a Lunar DXA. The COL1A1, ESR, VDR, IL-6, and OPG genes were amplified, and labeling of specific gene sequences was performed in a multiplex polymerase chain reaction using the osteo/check PCR kit from the whole blood of all subjects.

RESULTS

The bone mineral density (trochanteric and total bone mineral density values) of the fracture group was significantly decreased relative to the control group. We were not able to conduct statistical tests for the polymorphisms of the COL1A1, ESR, and VDR genes because our results were expressed in terms of frequency. Although they were not significant, we did examine differences in the IL-6 and OPG genes polymorphisms between the two groups. We concluded that increasing the number of cases will allow us to evaluate racial differences in femoral hip fracture risk by genotypes.

Association of Otosclerosis With Sp1 Binding Site Polymorphism in COL1A1 Gene: Evidence for a Shared Genetic Etiology With Osteoporosis

HYPOTHESIS

There is an association between otosclerosis and osteoporosis.

BACKGROUND

Both osteoporosis and otosclerosis are common bone diseases to which relatively large portions of the population are genetically predisposed. Recently, a strong association has been described between osteoporosis and an Sp1 binding site of putative functional significance in the first intron of the COL1A1 gene.

METHODS

We applied polymerase chain reaction-based restriction enzyme analysis to determine the polymorphic distribution of the Sp1 site in 100 patients with otosclerosis and 108 control subjects.

RESULTS

This study showed a significant association between otosclerosis and the COL1A1 first intron Sp1 site. The allelic frequency of the Sp1 site is very similar between otosclerosis and osteoporosis.

CONCLUSION

Some cases of otosclerosis and osteoporosis could share a functionally significant polymorphism in the Sp1 transcription factor binding site in the first intron of the COL1A1 gene.

Osteopenia and osteoporosis in women with breast cancer

Osteopenia and osteoporosis are prevalent in women. Epidemiologic studies show that the risk of breast cancer is greater in postmenopausal women with higher bone mineral density (BMD). Standard treatments for breast cancer such as adjuvant chemotherapy or hormonal therapy can increase bone loss, and hence may increase the risk of osteoporosis. Premenopausal women treated with standard adjuvant chemotherapy frequently develop permanent ovarian failure, or early menopause. Ovarian failure is associated with accelerated bone loss, and bisphosphonates may mitigate this bone loss in women treated with adjuvant chemotherapy. Tamoxifen preserves BMD in postmenopausal women; however, in premenopausal women tamoxifen may increase bone loss. Anastrazole, an aromatase inhibitor, is approved for adjuvant treatment of postmenopausal women with early-stage, estrogen receptor-positive breast cancer. With a follow-up duration of less than 5 years, anastrazole-treated women experience increased fractures relative to those treated with tamoxifen. The management of osteopenia and osteoporosis in women with breast cancer generally does not differ from women without breast cancer. Adequate dietary calcium and vitamin D intake, encouraging weight-bearing exercise, and counseling about the relationship between smoking and alcohol and bone loss are all prudent recommendations for overall health and may lessen bone loss and the risk of subsequent osteoporosis. BMD should be measured in women with chemotherapy-induced ovarian failure, and in those on aromatase inhibitors. Bisphosphonates reduce the bone loss associated with chemotherapy-induced ovarian failure, and clinical trials evaluating third-generation bisphosphonates in women with chemotherapy-induced ovarian failure are underway. As many women with breast cancer will be long-term survivors, increasing recognition of maintaining skeletal health is important.

Body composition and hip fracture type in elderly women

Many observations support the view that there are significant differences between patients sustaining trochanteric fractures and those sustaining cervical fractures of the hip. Our aim was to evaluate the association between soft tissue composition (fat and lean compartments) and the type of hip fracture sustained. Of 120 consecutive women affected by their first hip fracture admitted to our rehabilitation hospital 102 were included in this cross-sectional study. Body composition was assessed by DXA. Body fat mass was lower in the women with trochanteric fracture than in those with cervical fracture (difference between groups: 2.86 kg; 95% CI 0.10-5.61 kg; p=0.042). The percentage of fat was 30.75+/-8.77 (mean+/-SD) versus 34.75+/-7.29 (difference between groups: 4.00; 95% CI 0.84-7.16; p=0.014). In contrast, no meaningful differences in body lean mass were shown between the two groups. Logistic multiple regression showed that fat mass was associated with the type of fracture independently of age, height, weight, time between fracture occurrence and DEXA assessment, comorbidity, number of drugs in use, lean mass and bone mineral content. The logistic regression results were similar when fat percentage was substituted for fat mass. The data show that fat but not lean body mass is associated with the type of hip fracture, contributing to the definition of the differences between patients sustaining cervical or trochanteric fractures. We stress the importance of distinguishing the two types of fracture when clinical or epidemiological studies related to body composition, including those regarding nutrition or physical exercise, are performed.