PubMed · 11028437
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E Orwoll. 2000. Assessing bone density in men.. https://doi.org/10.1359/jbmr.2000.15.10.1867
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The unifying view that molybdenum is the essential component in nitrogenase has changed over the past few years with the discovery of a vanadium-containing nitrogenase and an iron-only nitrogenase. The principal question that has arisen for the alternative nitrogenases concerns the structures of their corresponding cofactors and their metal-ion valence assignments and whether there are significant differences with that of the more widely known molybdenum-iron cofactor (FeMoco). Spin-polarized broken-symmetry (BS) density functional theory (DFT) calculations are used to assess which of the two possible metal-ion valence assignments (4Fe(2+)4Fe(3+) or 6Fe(2+)2Fe(3+)) for the iron-only cofactor (FeFeco) best represents the resting state. For the 6Fe(2+)2Fe(3+) oxidation state, the spin coupling pattern for several spin state alignments compatible with S = 0 were generated and assessed by energy criteria. The most likely BS spin state is composed of a 4Fe cluster with spin S(a) = (7)/(2) antiferromagnetically coupled to a 4Fe' cluster with spin S(b) = (7)/(2). This state has the lowest DFT energy for the isolated FeFeco cluster and displays calculated Mössbauer isomer shifts consistent with experiment. Although the S = 0 resting state of FeFeco has recently been proposed to have metal-ion valencies of 4Fe(2+)4Fe(3+) (derived from experimental Mössbauer isomer shifts), our isomer shift calculations for the 4Fe(2+)4Fe(3+) oxidation state are in poorer agreement with experiment. Using the Mo(4+)6Fe(2+)Fe(3+) oxidation level of the cofactor as a starting point, the structural consequences of replacement of molybdenum (Mo(4+)) with vanadium (V(3+)) or iron (Fe(3+)) in the cofactor have been investigated. The size of the cofactor cluster shows a dependency on the nature of the heterometal and increases in the order FeMoco < FeVco < FeFeco.
HISTORY AND CLINICAL FINDINGS: A 27-year-old woman presented with chronic diffuse bone pain and skeletal deformities. Since the age of 3 years she had occipital hyperostosis. Since aged 13 years she had symptoms indicating spinal root involvement due to hyperkyphosis. For the last 6 years there was evidence of destructive and hyperplastic changes in the region of the middle ribs. Alkaline phosphatase (APL) had been elevated (> 250 U/l) for several years. Three years before the present admission the patient had been hospitalized elsewhere because of bone pain and had received intermittent infusions of pamindronate to a total of 600 mg. INVESTIGATIONS: Laboratory tests showed moderate rise in bone-specific APL and osteocalcin. Conventional x-ray examinations and computed tomography showed lesions in the occipital bone, sella turcica and ethmoid air cells. Several thoracic vertebral fractures were demonstrated. Skeletal scintigraphy indicated enrichment in the occipital and supraorbital regions, as well as in vertebrae and ribs. Dual energy x-ray absorptiometry (DEXA) showed osteopenia. Bone biopsy from the occipital lesion revealed fibrous dysplasia. TREATMENT AND COURSE: The diagnosis of fibrous dysplasia having been confirmed, cyclical treatment with i.v. pamidronate was given for 6 months. It was well tolerated and lessened the pain without changing the objective findings. CONCLUSION: In case of uncertain radiological and scintigraphic findings in the differential diagnosis of fibrous dysplasia, Paget's disease or bone tumor, it is essential to obtain a biopsy and, if available, perform gene analysis.
CONTEXT: Osteoporosis causes substantial morbidity and costs $13.8 billion annually in the United States. Measurement of bone mass by densitometry is a primary part of diagnosing osteoporosis and deciding a preventive treatment course. Bone mineral densitometry has become more widely available and commonly used in practice. OBJECTIVE: To review evidence about the value of various clinical applications of bone densitometry. DATA SOURCES: A MEDLINE search was performed to update previous meta-analyses of the relationship between various measurements of bone density and risk of vertebral and hip fracture. We used data from the prospective Study of Osteoporotic Fractures to estimate risk of fracture from bone density and age in postmenopausal women. STUDY SELECTION AND DATA EXTRACTION: When available, meta-analyses and systematic reviews are emphasized in the review. DATA SYNTHESIS: Bone mineral density (BMD) predicts fracture and can be used in combination with age to estimate absolute risk of fractures in postmenopausal white women. Hip BMD predicts hip fracture more strongly than other measurements of BMD. There are insufficient data to translate BMD results into risk of fracture for men and nonwhite women. The benefits of treatments to prevent fractures depend on BMD: women with osteoporosis have a greater risk of fractures and greater benefit from treatments than women without osteoporosis. CONCLUSIONS: Guidelines based on systematic reviews and a cost-effectiveness analysis have suggested that it is worthwhile to measure BMD in white women older than 65 years and perhaps to use risk factors to select younger postmenopausal women for densitometry. Other potential clinical applications of BMD that have not yet been adequately studied include screening men or nonwhite women, monitoring BMD in patients receiving treatment, and using BMD to identify patients who should be evaluated for secondary causes of osteoporosis.