Inclusion Criteria:  Patients (>18 years and <65 years), men and women, presenting a clinically and biologically authenticated PXE (genotype + phenotype) according to the international diagnostic criteria (25).  Efficient contraceptive method in woman of childbearing age at inclusion and during the overall study Patient affiliated to a social security insurance Signed informed consent Patient without acute complication linked or not to the pathology at the time of the study  NON-INCLUSION CRITERIA  Renal insufficiency (i.e. defined by a renal clearance <30ml / min / 1.73 m²) Known abnormality of the esophagus that would interfere with the passage of the drug, (e.g. esophagus stenosis). Patients with osteomalacia Patients with chronic diarrhea (> 1 month) Known sensitivity to Etidronate or its derivatives Pregnancy, lactating or fertile women who may wish to become pregnant within three years. Any other medical condition that may be considered in the opinion of the Principal Investigator. Use of bisphosphonate during last 5 years. Hypocalcemia (calcium <2.20 mmol/L and ionized calcium <1.15 mmol/L) *. Vitamin D deficiency <35 nmol/L *  Enrollment in another inteventional clinical trial which could interfere with the present study  After correcting the hypocalcemia and/or vitamin D deficiency, a participant is again suitable for participation in the trial, as long as the participant meets the inclusion criteria.