Etidronate for Arterial Calcifications Due to Deficiency in CD73 (ACDC)

An Open-label, Non-Randomized, Single-Arm Pilot Study to Evaluate the Effectiveness of Etidronate Treatment for Arterial Calcifications Due to Deficiency in CD73 (ACDC)

Background: Arterial Calcifications due to Deficiency in CD73 (ACDC) is a rare genetic disease. People with ACDC develop calcification in the arteries of the lower extremities as well as calcium deposit in the joints of the fingers, wrists, ankles and feet. The lower extremities calcification causes claudication because of severe ischemia requiring at time revascularization procedures. the calcium deposits in the joints causes severe debilitating pain in the hands and feet. Currently, there are no standard treatments for ACDC. Etidronate is a bisphosphonate that interferes with bone metabolism. It is approved to treat Paget's disease, a condition in which the bones are soft and weak and may be deformed, painful, or easily broken. It is also used to treat high blood calcium levels. Researchers want to see if it can be used to treat the calcifications of ACDC and improve pain and blood flow in the lower extremities and arthritic pain of the hands and feet. Objectives: - To see if etidronate is a safe and effective treatment for ACDC. Eligibility: - People between 18 and 80 years of age who have been diagnosed with ACDC. Design: Participants will be screened with a physical exam and medical history. They will also have imaging studies, including CT scan of the lower extremities, x-rays and DEXA bone scans, before starting treatment. Blood and urine samples will be collected. An exercise tolerance test will also be given and ABI (ankle brachial index will be measured. Participants will take etidronate by mouth once a day for 14 days every 3 months. They will be assigned an individualized 6- month drug schedule to follow. Participants will have regular study visits throughout the treatment period. These visits will involve imaging studies, full dental exams, and blood and urine tests. Participants will also have exercise tolerance tests and ABIs measured. Participants may also provide tissue samples for further study. Treatment will continue for up to 3 years as long as the side effects are not severe and the condition does not become worse. Participants will have a final follow-up visit after stopping treatment.

We have recently identified a novel genetic disease affecting nine known adults in whom de novo vascular calcifications develop in the lower extremity arteries and juxta-articular joint capsules of the fingers, wrists, ankles and feet. This rare disease results from bi-allelic mutations in the gene ecto-5-prime-nucleotidase (NT5E), encoding the CD73 protein. CD73, an enzyme involved in the extracellular ATP metabolic pathway, converts extracellular AMP to adenosine and inorganic phosphate. The clinical symptoms of this rare disease, termed ACDC (Arterial Calcifications due to Deficiency in CD73), include claudication of the calves, thighs, and buttocks, chronic ischemic pain of the feet at rest with threat of potential limb loss, and debilitating rheumatoid pain in the wrists and hands. Radiological and histological evaluations do not resemble classic atherosclerotic vascular calcification, since the calcification and dysplasia in ACDC occur in the medial portion of the arterial blood vessel wall. Data from patient-specific cell lines indicate increased activity of tissue non-specific alkaline phosphatase (TNAP), a key mediator of pathological ectopic tissue calcification, and thus reveals a potential therapeutic target. To date, no effective therapy exists for ACDC patients. However, since bisphosphonates are potent competitive inhibitors of TNAP activity and are widely used to modulate bone metabolism, they may beneficially alter vascular calcification. In addition, our preliminary in vitro studies demonstrate the effectiveness of etidronate, a nitrogen-containing bisphosphonate, in lowering TNAP activity in cells isolated from ACDC patients. Etidronate, and bisphosphonates in general, have proven safe and are well tolerated by most patients. This protocol provides for the administration of etidronate to ACDC patients, for whom no alternative treatment is available. Patients will be examined at the NIH Clinical Center bi-annually for 3 years. The primary objective of this clinical study is to test the effectiveness of etidronate in attenuating the progression of lower extremity arterial calcification and vascular blood flow based on CT calcium score and Ankle Brachial Index (ABI).

Participants diagnosed with Arterial Calcifications due to Deficiency in CD73 (ACDC) will receive Etidronate. Etidronate will be administered orally at total dose of 20mg/kg daily x 14 days, followed by 10 weeks off study drug (12 weeks = one cycle). Participants may receive up to 12 cycles of etidronate.

Didronel (etidronate disodium)- Didronel tablets contain either 200 mg or 400 mg of etidronate disodium, the disodium salt of (1-hydroxyethylidene) diphosphonic acid, for oral administration. This compound, also known as EHDP. regulates bone metabolism. It is a white powder, highly soluble in water. The 400 mg tablets are white capsule-shaped tablets with ED 400 on one side and G on the other side.

Visit on day 0 and visit at 36 month - Exploratory MRI studies may be employed to evaluate the lumen of the artery and degree of collateral vessels, given that the high degree of calcification is precluding that evaluation by CT.

Ankle-brachial Index at Rest at Pre-treatment, On-treatment and Post-treatment of Etidronate in Participants Diagnosed With ACDC

Ankle-brachial Index (ABI) at rest at pre-treatment, on-treatment and post-treatment of etidronate in participants diagnosed with ACDC. ABI is the ratio of the blood pressure in the lower and upper extremities obtained by dividing the blood pressure in an artery of the ankle by the blood pressure in an artery of the arm. Interpreting ABI values indicate the amount of arterial disease. Interpretation is as follows: > or equal to 1.3 is noncompressible vessel, > or equal to 1.0 is normal, 0.9 to 0.99 is borderline or equivocal, 0.7 to 0.89 is mild arterial disease, 0.5 to 0.69 is moderate arterial disease, and <0.5 is severe arterial disease.

Ankle-brachial Index After Exercise at Pre-treatment, On-treatment and Post-treatment of Etidronate in Participants Diagnosed With ACDC

Ankle-brachial Index (ABI) after exercise at pre-treatment, on-treatment and post-treatment of etidronate in participants diagnosed with ACDC. ABI is the ratio of the blood pressure in the lower and upper extremities obtained by dividing the blood pressure in an artery of the ankle by the blood pressure in an artery of the arm. Interpreting ABI values indicate the amount of arterial disease. Interpretation is as follows: > or equal to 1.3 is noncompressible vessel, > or equal to 1.0 is normal, 0.9 to 0.99 is borderline or equivocal, 0.7 to 0.89 is mild arterial disease, 0.5 to 0.69 is moderate arterial disease, and <0.5 is severe arterial disease.

Computed Tomography Calcium Score of Lower Extremities at Pre-treatment, On-treatment and Post-treatment of Etidronate in Participants Diagnosed With ACDC

Computed tomography (CT) Calcium Score of lower extremities at pre-treatment, on-treatment and post-treatment of etidronate in participants diagnosed with ACDC. According to Cleveland Clinic, a calcium score uses CT to detect calcium deposits in the coronary arteries of the heart. A higher coronary calcium score indicates a higher chance of significant narrowing in the coronary arteries and a higher risk of future heart attack. The Calcium Score range is as follows: zero is no evidence of Coronary Artery Disease (CAD), 1-10 is minimal evidence of CAD, 11-100 is mild evidence of CAD, 101-400 is moderate evidence of CAD and over 400 is extensive evidence of CAD. We applied the same concept to the arteries of the lower extremities. ACDC participants have an overwhelming amount of calcification in the lower extremity vasculature therefore their Calcium Scores are all out of range at baseline and during the study period.

Changes in Hand Joint Calcification Based on Hand X-ray Before and During Etidronate in Participants Diagnosed With ACDC

Changes in hand joint calcification are based on bilateral hand x-ray before and during Etidronate in participants diagnosed with ACDC as a composite score provided by a radiologist measuring calcium deposit volume (mm^3), calcium deposit density and number of calcifications observed in each finger joint. This is a new scoring system created by our team for the research study, so it has never been used before and healthy volunteer data is not available. However, healthy volunteers would be expected to have no joint calcifications in their hands, in sharp contrast with what we observe in ACDC patients. Density is subjectively defined as 0 equals no calcification, 1 equals barely visible, 2 equals visible with faint margins, 3 equals moderately dense and 4 equals fully dense. The range for the hand X-ray calcification score in this cohort was 288 (minimum) to 863 (maximum).

Simple Disease Activity Index Score at Pre-treatment, On-treatment and Post-treatment of Etidronate in Participants Diagnosed With ACDC

Simple Disease Activity Index (SDAI) score at pre-treatment, on-treatment and post-treatment of Etidronate in Participants Diagnosed With ACDC. The SDAI is a standard rheumatoid arthritis scores that provide treatment outcome measures on patient joint swelling and pain as well as participants ability to perform daily activity tasks. The SDAI is the sum of five parameters: tender and swollen joint count (based on a 28-joint assessment), patient and physician global assessment of disease activity and level of C-Reactive Protein (mg/dl, normal <1 mg/dl). Total score is defined as: remission as less than 3, low disease activity is between 3 to 11, moderate disease activity is between 11 to 26 and high disease activity is greater than 26. Maximum score possible score is 86 with high disease activity.

Duke Activity Status Index Score at Pre-treatment, On-treatment and Post-treatment of Etidronate in Participants Diagnosed With ACDC

Duke Activity Status Index (DASI) score at pre-treatment, on-treatment and post-treatment of Etidronate in Participants Diagnosed With ACDC. The DASI is an assessment tool used to evaluate the functional capacity of patients with cardiovascular disease (CVD), such as coronary artery disease, myocardial infarction, and heart failure. Positive responses are summed up to get a total score, which ranges from 0 to 58.2. Higher scores would indicate a higher functional capacity.

Peak Metabolic Equivalents (METS) During Treadmill Test at Pre-treatment, On-treatment and Post- Treatment of Etidronate in Participants Diagnosed With ACDC

Peak Metabolic Equivalents (METS) During Treadmill Test at Pre-treatment, On-treatment and Post- treatment of Etidronate in Participants Diagnosed With ACDC A symptom-limited treadmill progressive test (Gardner Protocol) with gradual increase in grade will be performed in accordance with standard practice to evaluation exercise capacity and pain on exertion in subjects with decreased peripheral arterial perfusion. This test will use a constant speed of 2 mph and gradual increase in grade of 2% every 2 minutes beginning at 0% grade. METS is a measure of how able a person is to tolerate exercise. No scales exists. METS is calculated by = METs x 3.5 x (your body weight in kilograms) / 200 = calories burned per minute.

INCLUSION CRITERIA Inclusion and exclusion criteria are to be assessed at Screening and Baseline prior to starting study drug. Each subject must meet the following criteria to be enrolled in this study: Subjects must be diagnosed with ACDC based on genetic tests confirming mutation(s) in NT5E and evidence of lower extremity arterial calcifications. Either gender and any ethnic background or race Age 18-80 years Willingness and legal ability to give and sign informed study consent Willingness to travel to NIH and local sites for scheduled protocol studies and treatment EXCLUSION CRITERIA Subjects who meet any of the following criteria will be excluded from the study: Subjects not diagnosed with ACDC Subjects <18 or >80 years of age Subjects who are unable or unwilling to sign an informed consent Severe renal impairment (estimated creatinine clearance/eGFR of < 30ml/min calculated using CKD-EPI equation) Longstanding diabetes mellitus (more than 10 years) Known abnormality of the esophagus that would interfere with the passage of the drug Known sensitivity to etidronate Pregnancy Any other medical or social condition that, in the opinion of the Principal Investigator, might put the subject at risk of harm during the study or might adversely affect the interpretation of the study data.

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