Hypophosphatasia (HPP) is a rare genetic disease characterized by a decrease in the activity of tissue non-specific alkaline phosphatase (TNSALP). TNSALP is encoded by the ALPL gene, which is abundantly expressed in the skeleton, liver, kidney, and developing teeth. HPP exhibits high clinical variability largely due to the high allelic heterogeneity of the ALPL gene. HPP is characterized by multisystemic complications, although the most common clinical manifestations are those that occur in the skeleton, muscles, and teeth. These complications are mainly due to the accumulation of inorganic pyrophosphate (PPi) and pyridoxal-5′-phosphate (PLP). It has been observed that the prevalence of mild forms of the disease is more than 40 times the prevalence of severe forms. Patients with HPP present at least one mutation in the ALPL gene. However, it is known that there are other causes that lead to decreased alkaline phosphatase (ALP) levels without mutations in the ALPL gene. Although the phenotype can be correlated with the genotype in HPP, the prediction of the phenotype from the genotype cannot be made with complete certainty. The availability of a specific enzyme replacement therapy for HPP undoubtedly represents an advance in therapeutic strategy, especially in severe forms of the disease in pediatric patients.

• The results were analyzed by analysis of variance and Pearson's correlation coefficient. RESULTS• Patients with relapsed calcium renal lithiasis present a greater BMD loss than those in the O or A groups.• Densitometry: T-score femur − 0.2 group O, − 0.5 group A, − 1.2 group B ( P = 0.001); T-score column − 0.6 group O, − 0.6 group A, − 1.3 group B ( P = 0.05).• A statistically significant negative correlation exists between values of β -crosslaps and T-score femur ( R = − 0.251; P = 0.009) and T-score column ( R = − 0.324; P = 0.001); thus, a higher concentration of β -crosslaps was accompanied by a lower value of the T-score and a greater loss of BMD.• A positive relationship is observed between β -crosslaps and osteocalcin ( R = 0.611; P < 0.001) and between calciuria and cocient β -crosslaps/osteocalcin ( R = 0.303; P = 0.001). CONCLUSIONS• A statistically significant relationship is shown between the loss of BMD and relapsed calcium renal lithiasis.• Determination of bone remodelling markers (i.e. osteocalcin and β -crosslaps) facilitates the diagnosis of osteopaenia/ osteoporosis in these patients. KEYWORDScalcium lithiasis, bone density, bone remodelling markers, bone densitometry What's known on the subject? and What does the study add? Hypercalciuria is related with bone mineral density loss.This study demonstrates the relationship between recurrent calcium nephrolithiasis and bone mineral density loss and their correlation with bone markers.Study Type -Aetiology (case control) Level of Evidence 3b OBJECTIVES• To show that a relationship exists between the loss of bone mineral density (BMD) and calcium renal lithiasis and that bone remodelling markers correlate with changes in BMD.• It is possible that many cases hypercalciuria are related to the increase of bone turnover and the predominance of bone resorption phenomena. PATIENTS AND METHODS• The present study comprised a transversal investigation in three groups: group O, without lithiasis; group A, with a single episode of lithiasis; and group B, with relapsed calcium renal lithiasis.• An analysis was made of body mass index; abdominal X-ray and/or urography and renal ultrasonography; osteocalcin and β -crosslaps bone markers; calcium and citrate concentrations in the urine; and femur and spinal column bone densitometry.

Calcium stone-forming patients have lower mean levels of vitamin D and a higher percentage of hypovitaminosis D than in non-stone-forming patients. This was only related to increased iPTH levels, with urine calcium and other lithogenic parameters having no obvious effect.

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