Protocol code and version: FIM-PXE-2016-01 Version 1.4

Trial title: "Response to oral lansoprazole of inorganic pyrophosphate levels in patients with Grönblad- Stranberg disease (Pseudoxanthoma Elasticum)"

Trial design: Double-blind, placebo-controlled, randomised, two-stage crossover clinical trial, with each patient serving as their own control and reducing the number of patients to confirm our hypothesis.

Principal Investigator: Dr. Pedro Valdivielso Felices Participating centres Virgen de la Victoria's Universitary Hospital in Malaga and Virgen de la Macarena's Universitary Hospital in Seville.

Duration of the trial: 12 months Expected start date: December 2019 Objectives: Principal:To verify the changes in plasma PPi, and the main molecules that regulate it (NPP1-3, TNAP) after oral administration of lansoprazole in patients diagnosed with PXE.

Description of treatment:

Selection:20 patients who meet all the criteria for inclusion and none for exclusion.

Randomisation and 1st stage: Patients will receive lansoprazole 30mg/day or their placebo for 8 weeks.

Wash-out: After 8 weeks, all treatment will be suspended for 15 days. 2nd stage (crossed): Treatment is crossed, each patient serves as his or her own control.

Evaluation variables:

1. Date of Birth
2. Sex.
3. Physical examination (anthropometry and vital signs)
4. Date of first symptom.
5. Date of final diagnosis
6. Ocular affectation (orange peel skin, complete striae angioides, lucentis, corrected visual acuity, cataracts, intraocular pressure, fundus (vascular flow, optic nerve drusen, retinal atrophy, neovascular membranes, macular thickness, colloid thickness).
7. Skin affectation (yellowish papules or plaques on the side of the neck or other areas of flexure and lax skin).
8. Vascular affectation (intermittent claudication clinic, angina and/or episode of acute myocardial infarction and/or non-embolic ischemic stroke, surgical or percutaneous revascularisation, cardiac murmur,10.)
9. History of renal lithiasis, arterial hypertension, diabetes mellitus, treatments, smoking and dyslipidemia.
10. Specific biochemical variables:

Inorganic pyrophosphate (IPP) NPP1 and NPP2.3: activity and mass concentration of the enzyme Non-specific tissue alkaline phosphatase (NTAP) and PHA. Osteocalcin: To check possible side effects on bone metabolism. 5'-Nucleotidas General analytical parameters (haemoglobin, haematocrit, MVC, MHC, platelets, neutrophils, prothrombin activity, TPTA, thrombin time, ferritin, PCR, glycaemia, urea, creatinine, cholesterol, triglycerides, HDL cholesterol, LDL cholesterol, uric acid, calcium, phosphorus, alkaline phosphatase, PTH). By means of routine clinical laboratory techniques. Number of patients: TOTAL : 20 patients(Competitive recruitment)

Inclusion Criteria:

1. Patients ≥18 years old

2. Patients diagnosed with PXE according to 2010 criteria by PLOMP et al.

3. At least, patients meet two of the following criteria:

   1. Retinal lesions such as Orange peel and/or Angioid streaks
   2. Skin lesions such as papules or yellowish plaques on the lateral face of the neck and / or flexures of the body (armpits, elbows, knees) or alterations in the skin biopsy with fragmentation and / or conglomerates of and / or calcification of the elastic fibers.
   3. A pathogenic mutation of the two alleles of the ABCC6 gene.

Exclusion Criteria:

1. Refusal of informed consent.
2. Vegetarian diet or extreme diets.
3. Pregnancy or its intention during the months of the study.
4. Age <18 years old
5. Known hypersensitivity to "prazoles" or proton pump inhibitors.
6. Intake of medications that may interfere with Lansoprazole and that cannot be withdrawn or modified in its form of administration to avoid such interference.
7. Prior taking of proton pump inhibitors, except for a wash out period of 15 days if the clinical situation of the patient allows it.

The masking of the drug to produce the cecum will be carried out by the Pharmacy on University Hospital Virgen de la Macarena accredited by the AEMPS. The medication for this clinical trial will be prepared by the Pharmacy on University Hospital Virgen de la Macarena in Seville ; the lansoprazole capsules and their placebo will be re-encapsulated in larger ones to maintain the cecum. The proposed doses used are those used in mild/moderate gastro-oesophageal diseases