Investigation of the relationship between osteoporosis and the collagenase gene by means of polymorphism of the 5'upstream region of this gene

Osteoporosis is a slowly progressing disease resulting from an imbalance between bone accretion and degradation. As interstitial collagenase is a key enzyme in the degradation of bone matrix, we investigated a possible relationship between the collagenase gene and osteoporosis. Analysis of an amplified genomic DNA fragment from -524 to +52 by denaturing gradient gel electrophoresis and sequencing allowed us to detect three dimorphic sites upstream of base -300, one of them leading to a BanI restriction site. None of the sites could be directly associated with osteoporosis. The allele frequencies of the three dimorphic sites were estimated. The interallelic ratios were high, thus providing new useful genetic markers for linkage analysis. When comparing these ratios in osteoporotic and nonosteoporotic subjects, no significant differences could be observed.

Is heritability a risk factor for postmenopausal osteoporosis?

We investigated heritability as a risk factor for the development of osteoporosis in two randomly selected populations of postmenopausal women and their premenopausal daughters. We determined the familial resemblance in bone mass at three sites; the distal forearm, lumbar spine, and proximal femur, premenopausally and with increasing maternal postmenopausal age. We also examined the bone mass of daughters in relation to mothers with and without osteoporotic fractures. Peak bone mass among premenopausal siblings was significantly correlated at all sites (r = 0.30-0.42, p less than 0.001). The same levels of resemblance were found between early postmenopausal mothers and premenopausal daughters. There was no significant difference in bone mass at any skeletal site between daughters of women with either peripheral or spinal fractures and daughters of women without fractures. We also examined familial resemblance with four biochemical markers of bone turnover (fasting urinary calcium and hydroxyproline, both corrected for creatinine, serum alkaline phosphatase, and plasma bone Gla protein). A generally significant resemblance were seen in premenopausal siblings (r = 0.25-0.39, hydroxyproline NS), but not between premenopausal daughters and postmenopausal mothers. We conclude that peak bone mass is hereditary in the distal forearm, lumbar spine, and proximal femur, but the mother-daughter resemblance explains only about 16% of the variability in daughters' bone mass. Furthermore, daughters of women with a moderate state of osteoporotic fractures are not substantially at an increased risk of having a low peak bone mass compared to the daughters of women without fractures.

Genetic variation in two bone-related proteins: is there an association with bone mineral density or skeletal size in postmenopausal women?

In an effort to determine if structural variation in proteins important in bone metabolism might influence bone mineral density (BMD) and thus be a determinant of susceptibility to osteoporosis in older women, the authors typed a group of 258 non-Black women (age 65-90) participating in the Study of Osteoporotic Fractures (SOF) for two polymorphic bone-related proteins, group specific component (Gc), also known as vitamin D-binding protein, and alpha 2HS glycoprotein (AHSG). These two proteins exhibit common structural variation in populations that can be detected by isoelectric focusing/immunoblotting of serum. An important function of Gc is the binding, solubilization, and transport of vitamin D sterols in the bloodstream while AHSG is a glycoprotein constituent of calcified cortical bone matrix. There are six common phenotypes of Gc and four of AHSG. Using Gc or AHSG phenotypes as categorical variables, statistical analyses were done to determine if bone mineral density of the proximal or distal radius or calcaneus differed by phenotype. Neither Gc nor AHSG phenotype demonstrated a statistically significant relationship with BMD at any site. Adjustments for age and degree of obesity did not substantively affect these results. Subsequent analyses to determine if phenotype of either of these proteins was associated with variables related to skeletal size showed an association of AHSG with height (P less than .02). This may indicate that AHSG phenotype is related to postmenopausal loss of height, or it may be a chance statistical finding.

No evidence for an effect of lactase deficiency on bone mass in pre- or postmenopausal women

The potential role for lactase deficiency in the development of low bone mass was examined in 342 adult female twins. Diminished lactase activity, defined as greater than 20 ppm increase in expired hydrogen at 2 or 2.5 h after an oral lactose load, was examined: (1) by comparing bone mass between members of twin pairs discordant for lactase activity; (2) by examining the linear association between bone mass and total expired hydrogen gas; and (3) by comparing all lactase-deficient individuals to those with persistent lactase activity. Among members of discordant (primarily DZ) pairs, the lactase-deficient member had greater bone mass 54% of the time. The correlations between the increase in expired hydrogen and bone mass at various sites were between -0.02 (femoral neck) and 0.11 (midshaft radius), suggesting no association between these variables. Finally, all lactase-deficient subjects were compared with those with normal lactase activity, regardless of twin status, and at each skeletal site the differences in bone mass were 1% or less. Thus, all primary hypotheses were not supported by these data; that is, in this large sample we could find no evidence of a detrimental effect of lactase deficiency on adult bone mass. However, baseline expired hydrogen was consistently and positively associated with bone mass at all sites, independently of age, suggesting the possibility that some aspect of intestinal function related to the activity of bacterial anaerobes may be positively associated with bone mass.

Mutation in a gene for type I procollagen (COL1A2) in a woman with postmenopausal osteoporosis: evidence for phenotypic and genotypic overlap with mild osteogenesis imperfecta

Mutations in the two genes for type I collagen (COL1A1 or COL1A2) cause osteogenesis imperfecta (OI), a heritable disease characterized by moderate to extreme brittleness of bone early in life. Here we show that a 52-year-old postmenopausal woman with severe osteopenia and a compression fracture of a thoracic vertebra had a mutation in the gene for the alpha 2(I) chain of type I collagen (COL1A2) similar to mutations that cause OI. cDNA was prepared from the woman's skin fibroblast RNA and assayed for the presence of a mutation by treating DNA heteroduplexes with carbodiimide. The results indicated a sequence variation in the region encoding amino acid residues 660-667 of the alpha 2(I) chain. Further analysis demonstrated a single-base mutation that caused a serine-for-glycine substitution at position 661 of the alpha 2(I) triple-helical domain. The substitution produced posttranslational overmodification of the collagen triple helix, as is seen with most glycine substitutions that cause OI. The patient had a history of five previous fractures, slightly blue sclerae, and slight hearing loss. Therefore, the results suggest that there may be phenotypic and genotypic overlap between mild osteogenesis imperfecta and postmenopausal osteoporosis, and that a subset of women with postmenopausal osteoporosis may have mutations in the genes for type I procollagen.