Free urinary glycosylated hydroxylysine as an indicator of altered collagen degradation in the mucopolysaccharidoses.

Extracellular matrix (ECM) disruption is known to be an early pathological feature of the Mucopolysaccharidoses (MPS). Collagen is the main component of the ECM and its metabolism could act as a useful indicator of ECM disruption. We have measured the specific collagen breakdown products; urinary free hydroxylated (Lys-OH) and glycosylated hydroxylysines (Lys-O-Gal and Lys-O-GalGlc) in MPS patients using a tandem liquid chromatography tandem mass spectrometry assay. A pilot study cohort analysis indicated that concentrations of lysine and Lys-OH were raised significantly in MPS I (Hurler) disease patients. Lys-O-GalGlc was raised in MPS II and MPS VI patients and demonstrated a significant difference between MPS I Hurler and an MPS I Hurler-Scheie group. Further analysis determined an age association for glycosylated hydroxylysine in control samples similar to that observed for the glycosaminoglycans. Using defined age ranges and treatment naïve patient samples we confirmed an increase in glycosylated hydroxylysines in MPS I and in adult MPS IVA. We also looked at the ratio of Lys-O-Gal to Lys-O-GalGlc, an indicator of the source of collagen degradation, and noticed a significant change in the ratio for all pediatric MPS I, II, and IV patients, and a small significant increase in adult MPS IV. This indicated that the collagen degradation products were coming from a source other than bone such as cartilage or connective tissue. To see how specific the changes in glycosylated hydroxylysine were to MPS patients we also looked at levels in patients with other inherited metabolic disorders. MPS patients showed a trend towards increased glycosylated hydroxylysines and an elevated ratio compared to other metabolic disorders that included Battens disease, Fabry disease, Pyridoxine-dependent epilepsy (due to mutations in ALDH7A1), and Niemann Pick C disease.

Biochemical markers of bone collagen type I metabolism.

This review focuses on the analysis of diagnostic value of the major bone remodeling markers, in particular synthesis and degradation markers of collagen type I. These include carboxy- and aminoterminal telopeptide, carboxy- and aminoterminal propeptide of procollagen type I, hydroxyproline, hydroxylysine, pyridinoline and deoxypyridinoline. Their measurement allows evaluating the structural and functional conditions and also the rate of metabolic processes in the bone tissue. The advantages and disadvantages of determination of these markers in the condition of different bone diseases were examined. It is shown that determination of bone collagen type I metabolism markers is the most informative for assessment of bone resorption, formation and turnover.

The relationship between body composition and the urinary excretion of deoxypyridinoline and galactosyl-hydroxylysine in children and adolescents.

The study intends to investigate the relationship of body composition (%fat, percent body fat; FM, fat mass; FFM, fat free mass; FA and MA cross-sectional fat and muscle area) to the urinary excretion of deoxypyridinoline (DPD) and galactosyl-hydroxylysine (Gal-Hyl). 231 healthy children and adolescents (age 5-19 years; 112 males) of the DONALD study were analyzed for FM and FFM by measuring 4 skinfold thicknesses, for DPD and Gal-Hyl in urine samples and for bone parameters, FA and MA at the forearm by peripheral quantitative computed tomography. In contrast to adrenarchal females, adrenarchal males with low %fat had low levels of DPD and Gal-Hyl. %fat was correlated with DPD in pre-adrenarchal males (r = 0.290) and females (r = 0.298). Cortical bone mineral density (BMDcort) was correlated with DPD (r = -0.351) in adrenarchal males. Controlled for BMDcort, FM was correlated with DPD in pre-adrenarchal males (r = 0.348), and FA was correlated with DPD in pre-adrenarchal females (r = 0.294). FFM was negatively correlated with Gal-Hyl in adrenarchal males (r = -0.436) and females (r = -0.338). Less than 40% of variance of excreted DPD and Gal-Hyl was explained by regression models based on parameters of body composition. The effect of body composition explains the minor part of variance of the urinary excretion of DPD and Gal-Hyl. The association of body composition to excreted DPD and Gal-Hyl was not explained by the effect of adipose tissue on bone formation and bone resorption.

Markers of bone turnover: biochemical and clinical perspectives.

Bone remodelling is a process by which bone grows and turns over. This process involves a series of highly regulated steps that depend on the interaction of two cell lineages, the osteoclasts and the osteoblasts. Information on metabolic activity of bone tissue are achieved with the determination, in blood and in urine, of biochemical products derived from the activity of this cells. The ability to determine bone turnover with biochemical markers has been enhanced considerably in recent years with the development of new assays for more sensitive and specific markers. These new markers can now replace the outdated and non-specific markers of bone remodeling such as serum total alkaline phosphatase (ALP) and urinary hydroxyproline (Hyp) determination. Biochemical markers of bone turnover can be classified according to the process that underlie in markers of bone formation, products of the osteoblast activity [bone ALP, osteocalcin (OC), procollagene I C- and N-terminal propeptides] and markers of bone resorption, products of the osteocalst activity [pyridinuim crosslinks, collagen I C- and N-terminal telopeptides (CTX-I and NTX-I), tartrate resistent acid phosphatase (TRACP) isoform 5b]. The interpretation of laboratory results should always include the consideration of potential sources of variability. Variation in the results of biochemical markers of bone metabolism can compromise their ability to characterize disorders of bone metabolism. Variation can be categorized into pre-analytical, analytical and biological sources. However, the determination of biochemical markers of bone turnover offers many advantages in clinical practice, since they are non-invasive, can be repeated often, and major changes occur in a short time.

Urine products of bone breakdown as markers of bone resorption and clinical usefulness of urinary hydroxyproline: an overview.

PURPOSE: The purpose of this study is to review the urine products of bone breakdown as markers of bone resorption and usefulness of urinary hydroxyproline. DATA: Related researches published in 1985 - 2000 were systematically reviewed. RESULTS: Bone markers could be used for early diagnosis of bone metabolic diseases. Biochemical markers of bone resorption that reflect osteoclast activity and/or collagen degradation provide a new and potentially important clinical tool for the assessment and monitoring of bone metabolism. Assessment of bone resorption can be achieved with measurement of urinary hydroxylysine glycosides, urinary excretion of the collagen pyridinium cross-links, urinary excretion of type I collagen telopeptide breakdown products (cross-linked telopeptides) and urinary hydroxyproline. CONCLUSION: Urinary hydroxyproline has been in use as a marker of bone resorption, but it lacks sensitivity and specificity. It is a modified amino acid that is a metabolic product of collagen breakdown. Hydroxyproline may be released either free or with fragments of the collagen molecule attached during bone resorption, and it is also liberated by the breakdown of complement and nonskeletal collagen.

Collagen markers deoxypyridinoline and hydroxylysine glycosides: pediatric reference data and use for growth prediction in growth hormone-deficient children.

BACKGROUND: In children and adolescents, markers of bone and collagen metabolism reflect the dynamics of skeletal growth and development. The aim of this study was to assess the relationship of the urinary collagen markers deoxypyridinoline (DPD) and hydroxylysine (Hyl) and its glycosides [galactosyl-Hyl (Gal-Hyl) and glucosyl-Gal-Hyl] with growth. METHODS: Urine samples from 240 apparently healthy children and adolescents (6-19 years; 124 girls) and from 51 prepubertal children with growth hormone (GH) deficiency (3-14 years; 14 girls) were analyzed. Urinary Hyl and its glycosides were quantified by HPLC, and DPD was assessed by chemiluminescence assay. Urinary concentrations of all markers were related to urinary creatinine. RESULTS: Multiple regression analysis revealed that only age and height velocity were independently associated with these markers in healthy children. In GH-deficient patients, the urinary excretion of both analytes after 4 weeks of GH therapy correlated significantly with the height increase during the first treatment year (r = 0.79 for Gal-Hyl; r = 0.70 for DPD; P <0.001 each). In a multivariate linear regression model using Gal-Hyl concentrations at 4 weeks, baseline concentrations of insulin-like growth factor 1 and height velocity after 3 months accounted for 80% of the variability in height gain during the first treatment year. A model using DPD concentrations at 4 weeks, in place of Gal-Hyl concentrations, as well as baseline concentrations of insulin-like growth factor 1 and height velocity after 3 months accounted for 83% of the variability. CONCLUSIONS: These urinary bone and collagen markers give some early indication of growth response, but the prediction of an individual marker is too imprecise to serve as a basis for clinical decisions. Markers of bone and collagen metabolism might be more useful as components of multivariate growth prediction models.

Urinary collagen metabolite excretion in amyotrophic lateral sclerosis.

Collagen abnormalities of the spinal cord and the skin have been reported in patients with amyotrophic lateral sclerosis (ALS). The urinary concentrations of the hydroxylysine glycosides, i.e., glucosylgalactosyl hydroxylysine (glu-gal Hyl) and galactosyl hydroxylysine (gal Hyl), indicate the tissue origin of the collagen metabolites and the rate of the degradation of collagen. We measured the urinary levels of glu-gal Hyl and gal Hyl in 12 ALS patients, 10 diseased control subjects with other neurologic or muscular diseases (Control Group A), and 10 healthy control subjects (Control Group B). The urinary level of glu-gal Hyl in ALS patients was significantly lower than in the two control groups. In addition, a significant negative relationship between glu-gal Hyl urinary level and duration of illness was found in ALS patients. There was no marked difference in the urinary level of gal Hyl between ALS patients and the control groups. Our data suggest that the decreased urinary level of glu-gal Hyl may be useful in assessing the alteration in collagen metabolism in ALS and may have a relationship with the progression of ALS.

[Bone complication in diabetes subjects with good metabolic control and without longterm complications: certain problems. Part II. Basal parameters of bone turnover]. / Powiklania kostne u chorych z dobrze wyrównana i nie powiklana cukrzyca typu 1 i 2--wybrane zagadnienia. Czesc II: Podstawowe wskazniki obrotu kostnego.

The resorption and osteogenesis equilibrium is commonly known basal condition of bone tissue homeostasis. For the purpose of bone turnover analysis in the group of good controlled diabetic patients without any diabetic complications basal biochemical parameters of osteogenesis and resorption were estimated. During low-calcium diet conditions both serum concentration and urine excretion of creatinine, hydroxyproline, hydroxylysine and uric acid were investigated. Serum alkaline phosphatase activity and oxalic acid urine excretion were also measured. As the result of the study the higher serum alkaline phosphatase activity and hydroksyproline urine excretion in type 1 diabetic patients as well as higher hydroxyproline and hydroxylysine urine excretion in type 2 diabetic patients were found.

A rapid and simple method for quantitation of urinary hydroxylysyl glycosides, indicators of collagen turnover, using liquid chromatography/tandem mass spectrometry.

Some glycosides of hydroxylysine, viz., alpha-1, 2-glucosylgalactosyl-O-hydroxylysine and beta-1-galactosyl-O-hydroxylysine, appear to be good indicators of collagen turnover. A simple liquid chromatography/tandem mass spectrometry (LC/MS/MS) method is proposed for measuring these analytes in urine, with no sample preparation except for a dilution step. Quantitation is performed using external calibration with no internal standard. A preliminary survey indicates good intra- and inter-day reproducibility (better than 5 and 8%, respectively). With the present method, the estimated limits of detection (S/N > 3) in urine are 0.8 and 0.5 microM/L for beta-1-galactosyl-O-hydroxylysine and alpha-1,2-glucosylgalactosyl-O-hydroxylysine, respectively. The method is proposed as a robust tool for a large-scale research investigation on collagen turnover.

Urinary galactosyl-hydroxylysine in postmenopausal osteoporotic women: A potential marker of bone fragility.

Alterations of the collagen matrix, e.g., increased hydroxylation and glycosylation of lysyl residues in collagen I, were found in human osteoporotic bone, and it was suggested that they could alter the mechanical properties of skeleton. To test this hypothesis, we evaluated the content of galactosyl-hydroxylysine (GHYL) in bone collagen, as assessed by its urinary excretion, and related it to the occurrence of fracture. Two hundred and fifteen unselected postmenopausal women with osteoporosis were divided in two subgroups (comparable for age, age of menopause, bone mineral density, and biochemical parameters of bone turnover) on the basis of the history of fragility fracture; 115 patients had suffered no fracture and 100 patients had suffered one or more fractures 3 or more years before. Four urinary markers of bone turnover (hydroxyproline, cross-linked N-telopeptide, free deoxypyridoline, and GHYL) were evaluated in all patients. There was no difference between the two groups with regard to all the parameters studied except for GHYL, which was significantly higher in the group with a history of fracture (1.35 +/- 0.82 mmol/mol of creatinine [Cr] versus 1.03 +/- <0.48 mmol/mol Cr, p < 0.001); this marker did not correlate with other markers of bone remodeling in the fracture group, indicating a possible defect in bone collagen. In conclusion, provided that increased levels of urinary GHYL do reflect overglycosylation of hydroxylysine in bone collagen, the GHYL may be considered a marker of bone collagen quality. Our results, showing higher urinary GHYL in osteoporosis patients with fracture, seem to confirm this suggestion.

Serum galactosyl hydroxylysine as a biochemical marker of bone resorption.

BACKGROUND: Serum-based biochemical markers of bone resorption may provide better clinical information than urinary markers because direct comparison with serum markers of bone formation is possible and because the within-subject variability of serum markers may be lower. We describe a method for the measurement of free beta-1-galactosyl-O-hydroxylysine (Gal-Hyl) in serum. METHODS: The assay used preliminary ultrafiltration of serum, dansylation, and separation by reversed-phase HPLC with fluorescence detection. Healthy subjects were recruited from population-based studies of bone turnover. RESULTS: The within-run (n = 15) and between-run (n = 15) CVs were 7% and 14%, respectively, at a mean value of 48 nmol/L. In women and pubertal girls, serum free Gal-Hyl correlated with urine free Gal-Hyl (r = 0.84; P <0.001). Serum Gal-Hyl was higher during puberty and increased after menopause. The fractional renal clearance of free Gal-Hyl relative to that of creatinine was 0.90 (95% confidence interval, 0.82-0.98). Serum free Gal-Hyl decreased by 36% (SE = 4%) in 14 patients with mild Paget disease treated with an oral bisphosphonate, and this decrease was significantly (P <0. 001) greater than that seen for either serum tartrate-resistant acid phosphatase (9%; SE = 4%) or serum C-terminal telopeptide of collagen I (19%; SE = 8%). CONCLUSION: Serum free Gal-Hyl may be useful as a serum marker of bone resorption.

Assay for 5-hydroxylysine and L-lysine in human and rat urine and in bone by gas chromatography.

An accurate method for the determination of collagen to study its distribution and turn-over in different tissues is described. 5-Hydroxylysine (5Hylys) is an amino acid that is apparently present in no other protein except collagen and, as it is metabolised only to a minor degree compared with 4-hydroxyproline (4Hypro), it has been suggested as a better marker of the collagen metabolism. Interest in this amino acid has increased recently because the levels of 5Hylys in urine and in different tissues may offer a new basis for detecting pathologies of the collagen molecule. This paper describes a method for the quantitative determination of 5Hylys and lysine (Lys) by gas chromatography (GC) in human and rat urine and in rat bone. The limit of detection was 350 pmol ml-1 for 5Hylys and 200 pmol ml-1 for Lys for all the biological samples. This method therefore provides a complete view of the metabolism of this amino acid and of the tissue it comes from.

Development of an immunoassay for urinary galactosylhydroxylysine.

Galactosylhydroxylysine (GHL) is released during bone resorption and has been shown to be elevated in subjects with metabolic bone loss. GHL is relatively specific for bone, it is not recycled or significantly metabolized during collagen turnover, and the levels are not influenced by diet. Previous measurements of GHL levels in urine have been performed using reverse-phase high performance liquid chromatography following pre-column derivatization. We produced polyclonal antibodies to GHL using GHL purified from sea sponges and developed an immunoassay that can recognize GHL in urine. The antibodies have minimal cross-reactivity with a physiological mixture of amino acids (< 1%), galactose (< 0.2%), lactose (< 0.3%), and glucosylgalactosylhydroxylysine (< 1%). This competitive immunoassay requires no dilution or pretreatment of the samples and provides a rapid and easy method for the evaluation of GHL in urine. Analysis of clinical samples from normal individuals, post-menopausal women, osteoporotic patients and individuals with Paget's disease show that the assay can discriminate between groups with differing levels of bone resorption as well as deoxypyridinoline (Dpd).

A proposal for standardizing urine collections for bone resorption markers measurement.

Diurnal variations in the excretion of bone resorption markers were assessed in order to identify the type of urine collection which provides the most information on bone resorption rate and its relation to measuring bone dynamics in a postmenopausal population. Sixty women, ages 43-67 and without disease or treatment known to affect bone mineral density, were divided into two groups on the basis of femoral mineral density T-score: <1.5 (Group I), >1.5 (Group II). Bone formation was assessed by measuring bone alkaline phosphatase activity and osteocalcin concentration, bone resorption by urinary hydroxyproline, pyridinoline and deoxypiridinoline, N-telopeptide, galactosyl hydroxylysine, and CrossLaps. To identify the more appropriate collection times, urine samples were collected from 7 am to 3 pm; from 3 pm to 11 pm; from 11 pm to 7 am. Twenty-four hour urine collection and first morning void urine samples were also measured. The findings suggest that nocturnal collection and first morning void samples provide the most reliable data on the rate of bone degradation, possibly showing bone loss not only in osteopenic patients but also in women with a low T-score. Nocturnal and first morning samples should therefore be recommended in order to standardize sample collection, as they enable an accurate assessment of bone resorption markers and improved comparability to results from different studies, as well as a less cumbersome collection modality.

Effects of 1- and 6-month spaceflight on bone mass and biochemistry in two humans.

The bone mineral density and the biochemical parameters exploring bone cell activities were analyzed in two cosmonauts who spent 1 and 6 months, respectively, in the Russian MIR station. Measurements were performed before the flight, after the flight, and after a recovery period. At the end of the first month, peripheral QCT measurements indicated a slight decrease of trabecular bone mass in the distal tibial metaphysis. However, after 6 months of spaceflight, a more marked loss of trabecular and cortical bones was observed in the tibia, and was still significant after 6 month recovery in the trabecular compartment, whereas a decrease was no longer observed in the cortical envelope. No change was observed in either compartment of the distal radius at any time. Ultrasound BUA of the calcaneus was greatly reduced by the first month, followed by a more dramatic decrease after month 6. Ultrasound SOS detected no change. Parameters reflecting bone formation activity appeared to be depressed after both missions. In contrast, no dramatic change in resorption parameters was observed, except for a trend toward an increase in pyridinoline. In conclusion, the lower weight-bearing bones appeared more sensitive than the upper ones in terms of spaceflight-induced bone loss. This probably explained the absence of marked systemic biochemical data changes. This study further suggests that recovery in the tibial trabecular compartment 6 months after landing was not completed after a 6 month mission.

Ovariectomy in the rat induces a rapid increase in the urinary excretion of hydroxylysine glycosides and non-reducible crosslink residues.

The ovariectomized rat is the most commonly used animal model of human postmenopausal osteoporosis, exhibiting a high rate of bone turnover with resorption exceeding formation. At present, bone turnover is quantified directly by dynamic histomorphometry. The aim of the present study was to determine whether the measurement of the urinary output of some specific bone collagen catabolites--pyridinolines and hydroxylysine glycosides--could be used to indirectly monitor the initial phase of bone turnover increase in ovariectomized 90-day-old rats. Ninety-day-old female rats were randomly divided into three groups (n = 6): ovariectomized, sham-operated and non-treated controls. Urine samples (24 h) were collected 6 days before surgery and twice weekly for the 4 weeks following ovariectomy. Urinary excretion of pyridinoline (PYD), deoxypyridinoline (DPD), glucosyl-galactosyl-hydroxylysine (GGHYL) and galactosyl-hydroxylysine (GHYL) were measured. As expected, ovariectomy was associated with a significant decrease in bone mineral density in both the proximal tibial and distal femoral metaphysis. Compared with both sham-operated and control animals, ovariectomized rats showed significant increases in PYD, GGHYL, and GHYL urinary output 8 days after surgery and in DPD output after 15 days. These changes were maintained throughout the study. The results confirm that measurement of the urinary excretion of pyridinolines and hydroxylysine glycosides represents a powerful tool for detecting the onset of bone turnover in ovariectomized 90-day-old rats.

A comparative study on biochemical markers of bone collagen breakdown in post-menopausal women.

The aim of this study was to compare urinary galactosylhydroxylysine (GHyl) and deoxypyridinoline (d-Pyr) as biochemical markers of bone resorption in post-menopausal women treated and untreated with estrogen and cyclic etidronate. Fasting urinary GHyl, D-Pyr, pyridinoline, serum osteocalcin and total alkaline phosphatase were measured in three subgroups, i.e. post-menopausal women undergoing hormone replacement therapy, untreated post-menopausal women and post-menopausal women with low BMD treated with disodium etidronate. The results indicated that GHyl did not significantly discriminate between untreated post-menopausal women and estrogen replated ones unless an osteoporotic untreated group was selected. d-Pyr and GHyl showed similar performances when their values after bisphosphonate treatment were compared to those found in untreated post-menopausal women, thus suggesting that both markers were equal in their ability to detect the bone response to cyclic etidronate administration. This observation further proves the statement that GHyl is prone to confounding factors under estrogen therapy but it is adequate as is d-Pyr in monitoring the bone response to bisphosphonate treatment.

Effect of an oral calcium load on urinary markers of collagen breakdown.

Aim of this study was to investigate whether osteoclast activity changes as a consequence of even mild physiological perturbation of plasma calcium as such induced by an oral calcium load. Osteoclast activity was determined indirectly by measuring, in spot urines at two and four hours after oral calcium load, the urinary excretion of hydroxylysylpyridinoline (Pyr), deoxylysylpyridinoline (D-Pyr), hydroxyproline (Hyp) and galactosyl-hydroxylysine (GHyl). The occurrence of the metabolic perturbation of plasma calcium homeostasis was assessed by measuring three indexes: i.e. calcemic response, PTH reduction and calciuric response at times following oral calcium loading. A significant fall of urinary D-Pyr and Pyr followed the perturbation of calcium homeostasis induced by the oral calcium load in two groups of healthy young adult and postmenopausal women. The highest mean percent reduction was observed for D-Pyr and was quantitatively similar in the two groups. Since urinary D-Pyr is the most specific bone resorption marker, it may be inferred that the perturbation of plasma calcium homeostasis induced by an oral calcium load is able to acutely inhibit osteoclast activity. This supports the view that osteoclasts are involved in the short-term error correction of plasma calcium.

Longitudinal changes in bone mineral density and bone turnover in postmenopausal women with primary hyperparathyroidism.

The aims of this study were to determine 1) whether primary hyperparathyroidism (PHPT) is associated with accelerated bone loss in postmenopausal women, 2) whether bone mineral density (BMD) and bone turnover change to a similar extent with surgery and hormone replacement therapy (HRT) in these patients, and 3) whether biochemical markers of bone turnover measured at baseline can be used to predict the change in BMD in these patients after different therapies. We studied 33 postmenopausal women with PHPT; their ages at the time of study ranged from 48-80 yr (mean +/- SD, 63 +/- 10). Total body (TB), lumbar spine (LS), and femoral neck (FN) BMD and biochemical markers of bone turnover were measured at baseline and 10-30 months (19 +/- 5) after parathyroid surgery, HRT, or no treatment. BMD was measured in 33 age-matched healthy controls at baseline and at a mean of 24 months. Baseline biochemical markers of bone turnover were measured in controls. In PHPT at baseline, the mean z-score of BMD was -1.25 at TB (95% confidence interval, -1.64 to -0.86), -0.95 at LS (-1.37 to -0.53), and -1.30 at FN (-1.65 to -0.95), whereas the mean z score was 0.45 for serum carboxy-terminal propeptide of human type I procollagen (0.02-0.89), 1.05 for bone alkaline phosphatase (0.38-1.71), 2.38 for 24-h urinary excretion of cross-linked N-terminal telopeptide of type I collagen (NTx; 1.63-3.13), and 2.36 for 24-h urinary excretion of galactosyl hydroxylysine (1.97-2.74). After surgery and HRT, BMD increased and bone turnover decreased during the follow-up. In the untreated group, BMD decreased at TB and FN, and levels of bone alkaline phosphatase, NTx/creatinine, and galactosyl hydroxylysine/creatinine increased. When the rate of change in BMD (percentage per yr) was compared with that in the control group, bone gain was significant at all three skeletal sites after surgery and HRT, and bone loss was significant at TB and FN, but not at LS, in the untreated group. There was a weak, but significant, correlation between baseline urinary NTx and the change in femoral neck BMD in the untreated group (r = -0.36; P = 0.05). We conclude that untreated postmenopausal women with PHPT have low BMD resulting from accelerated bone loss at the TB and FN. Surgery and HRT both restore BMD and bone turnover toward normal in postmenopausal women with PHPT. A single measurement of bone turnover is insufficient to predict BMD changes in individual patients with PHPT.