A variation in Bone Alkaline Phosphatase levels that correlates positively with bone loss and normal levels of aminoterminal propeptide of collagen I in girls with anorexia nervosa
Introduction
The new assays for parameters of bone and collagen metabolism have generated much interest among researchers in the field of adult metabolic bone disease [1] and now are increasingly used by paediatricians. However, bone metabolism differs considerably between children and adults. Thus there is a specific paediatric perspective of bone metabolism and of the biochemical parameters used in its evaluation that must be taken into account together with the type of pathology under study [2].
With respect to biochemical markers of bone formation, in a recent report by our group [3] we found that among the available biochemical markers of osteoblast activity – total and bone alkaline phospatase (TAP and bAP, respectively), osteocalcin (BGP), procollagen I aminoterminal propeptide (PINP) and procollagen I carboxyterminal propeptide (PICP) – serum bAP and PINP showed the highest diagnostic accuracy for detecting the alterations in bone remodelling that take place in postmenopausal osteoporosis. In the field of biochemical markers of bone resorption, the new marker C-telopeptide of type I Collagen (CTX) has also demonstrated a high specificity and sensitivity in the study of bone turnover in this pathology [4]. In a recent work [5] we found that the urinary β-isomerized form of CTX is an adequate parameter to study bone resorption in anorexic adolescents.
Anorexia nervosa (AN) is a chronic eating disorder, characterised by self-imposed semistarvation, that affects 1% of adolescent females. Osteoporosis is one of the important medical complications associated with AN [6]. In spite of this fact, there are few and contradictory data available concerning bone turnover in this population [7]. The aim of this study was to compare the usefulness of bAP and PINP in the study of bone remodelling in AN and their possible correlation with the degree of osteopenia in this pathology. In order to help in the interpretation of the results, levels of urinary CTX of these patients have also been included.
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Materials and methods
We studied 41 women with established AN, as defined by criteria of the American Psychiatric Association [8], with a mean age±standard deviation of 18.5±2.2 years (range 16–24 years) and 31 healthy control women, aged 19±2.3 years (range 16–24 years). The study was approved by the ethics committee of our hospital.
The AN group included women with amenorrhea (n=25), as well as those without amenorrhea who were on oral contraceptive treatment (n=16). The evolution time of AN was 3.9±1.8 years. Ten
Results
Table 1 shows the levels of serum bAP, PINP and urinary β-CTX in control girls and patients with AN. The degree of osteopenia expressed as the z-score of BMD in the anorexic group is also shown. All the patients showed BMD values under the mean value corresponding to their age (negative z-score). A high degree of osteopenia (mean value of z-score=−3.2) was observed in the anorexic group. With the exception of two patients whose values of z-score were −0.9 and −1.4, all the anorexic girls
Discussion
As can be expected, girls with AN presented a high degree of osteopenia compared with age-matched healthy girls. When we analysed the possible correlation between this observed osteopenia and the biochemical markers of bone formation bAP and PINP, we found a significant correlation with bAP, i.e. a greater bone loss corresponds to higher levels of bAP. However, there is no correlation between osteopenia and PINP levels. This correlation between bAP and BMD z-score could seem to be in
Acknowledgements
We wish to thank Dr. G. Morandé, Department of Psychiatry of the Niño Jesús Hospital, for providing us with the anorexic patients and the students of Ntra. Sra. de las Maravillas School and Nursing School of the Fundación Jiménez Dı́az (Madrid) for their kind collaboration.
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