Institution of an Italian Multicenter Database of Patients Affected by Diseases of Phosphate Metabolism

The goal of this observational study is to create, manage and analyze a multicenter national database of patients affected by diseases of phosphate metabolism, aimed at collecting and studying anamnestic, diagnostic, genetic, clinical, and therapeutic data in a relatively wide number of patients with these rare inherited metabolic disorders in Italy.

The study will include 28 specialist clinical centers of endocrinology, pediatric endocrinology, and pediatrics, located throughout the Italian territory, and to which patients refer from all the 20 regions of Italy.

Data will be collected over time, both in retrospective and prospective manners, during the 10-year duration of the study, starting from the recruiting visit (basal visit) and then during each follow-up visits patients will undergo for the control of disease at the recruiting clinical centers.

Collected data will include both the most classic traits of each disease and the less common ones, with the final goal of refining and deepening medical knowledge in the field of these rare inherited metabolic disorders, and, thus, to be able to define optimal tailored diagnostic, clinical, and therapeutic management of patients, improving their quality of life.

The main aspects this observational study aims to assess and clarify are:

1. Evaluation of prevalence and incidence of diseases of phosphate metabolism in Italy, globally and for single different disorders
2. Clinical and biochemical characterization of different diseases of phosphate metabolism (according to single disorders and different genetic base), through both cross-sectional and longitudinal analyses of collected data
3. Evaluation of skeletal health and bone fragility in patients with diseases of phosphate metabolism, globally and based on single phosphate metabolism disorder, gender, and age
4. Self-evaluation of health-related quality of life in patients with a disease of phosphate metabolism
5. Over time evaluation of responses to therapies in patients with diseases of phosphate metabolism.

The study will include a single cohort of female and male patients of any age, affected by a disease of phosphate metabolism. The study does not include either any control group/comparison group or healthy volunteers.

The study itself does not involve any medical intervention or drug administration. Therapies for which response outcomes will be collected in the database, are those commonly employed for the treatment of diseases of phosphate metabolism, regardless of patients' inclusion in this observational study.

1. Background and rationale

   Phosphorus is one of the most abundant elements in the human body, where it is found, mainly in the form of phosphate salts, in quantities of about 500-700 grams, of which about 85% is concentrated in bone tissue, where it is an important constituent of hydroxyapatite crystals. In soft tissues, phosphate is mainly found in the intracellular compartment as an essential component of various organic compounds, including nucleic acids and phospholipids of the cell membrane.

   The concentration of circulating extracellular phosphate is finely regulated by hormones such as parathyroid hormone (PTH), the active form of vitamin D (1,25-dihydroxyvitamin D or calcitriol), and fibroblast growth factor 23 (FGF23). The latter belongs to a family of proteins, specifically responsible for regulating phosphate metabolism, which are called phosphatonins in their complex, and include FGF23, Phosphate Regulating Endopeptidase X-Linked (PHEX), Polypeptide N-Acetylgalactosaminyltransferase 3 (GALNT3), Klotho. Under normal conditions, the coordinated action of phosphotropic hormones modulates intestinal absorption of this mineral, its renal reabsorption, and bone mineralization, maintaining the balance between absorption and excretion and ensuring a normal blood concentration of phosphate between 2.5 and 4.5 mg/dl (0.81-1.45 mmol/L) in the adult organism. Bone phosphate serves as a deposit, capable of buffering changes in plasma and intracellular levels of phosphate. Alterations in the mechanisms that regulate phosphate metabolism are responsible for the development of a group of rare disorders that are collectively defined as phosphate metabolism diseases, and include diseases caused by excess phosphate (hyperphosphatemic disorders), such as calcinosis, and diseases caused by deficiency of phosphate (hypophosphatemic disorders), such as hypophosphatemic rickets.

   Phosphate metabolism diseases are classified as rare diseases. As reported by the "Osservatorio Malattie Rare (OMAR)", in the European Union a disease is defined as rare when its prevalence, understood as the number of cases present in a given population, is less than 0.05 percent of the population (no more than one case in every 2,000 people). The rarity of these diseases makes them difficult to study, and unfortunately, in many cases, scientific and medical knowledge of rare diseases is scarce and inadequate, and limited to few case reports. Due to the lack of sufficient medical and scientific knowledge, many patients affected by rare diseases remain undiagnosed and their diseases remain unrecognized. It is, therefore, essential that doctors and researchers working in the field of rare diseases increasingly work in networks to share the results of their research and to progress more effectively in the knowledge and clinical management of these diseases. In this perspective, implementing and detailing as much as possible the knowledge on the epidemiology, clinical and therapeutic history, primary and secondary manifestations of diseases of phosphate metabolism and the response to employed therapies, both in cross-sectional and longitudinal manners, with constant follow-up assessments of patients is essential not only to improve the clinical management of single patients, but also to allow better planning of social, political and health interventions for these pathologies and, overall, improve the quality of life of patients.

   For this reason, it is extremely important to create a national multicenter database, such as the one proposed by this study, which is able to collect a relatively high number of patients affected by diseases of phosphate metabolism, whose cases are carefully studied in every aspect, both retrospectively and prospectively, following the course of the disease over time. Such a database has never been prepared in Italy before, and the availability of clinical data relating to diseases of phosphate metabolism has been limited to individual clinical cases to date.

   The collection of clinical data of patients affected by diseases of phosphate metabolism, both retrospectively (during the study recruitment visit) and prospectively (during follow-up visits), will allow for an epidemiological evaluation of these pathologies in Italy and for both cross-sectional and longitudinal analyses of the collected data, with particular attention to the clinical evolution, response to therapies, and quality of life of the patients.
2. Main aim and specific objectives

Main goal of this observational study is to create, manage and analyze a retro-prospective multicenter national database of patients affected by diseases of phosphate metabolism, aimed at collecting and studying anamnestic, diagnostic, genetic, clinical, and therapeutic data in a relatively wide number of patients with these rare congenital metabolic disorders in Italy.

Such a database will allow for an epidemiological evaluation of prevalence and incidence of diseases of phosphate metabolism in Italy, and to collect case history of patients whose clinical cases will be studied in detail and followed over time up to 10 years after the recruitment in the study, in order to refine knowledge in the field of these rare disorders.

Specific objectives of the studies are:

1. Creation of an Italian centralized multicenter database of patients affected by diseases of phosphate metabolism, through the collection of patients at 28 specialist clinical centers of endocrinology, pediatric endocrinology, and pediatrics, located throughout the Italian territory and visiting patients from all the 20 regions of Italy.
2. Collection of a relatively high number of patients affected by diseases of phosphate metabolism
3. Retrospective collection of data about diseases of phosphate metabolism, at the time of the recruiting visit.
4. Continuous and updated prospective collection of patients' data over time, starting from the first recruiting visit up to 10 years after the recruitment in the study.

6. Evaluation of prevalence and incidence of diseases of phosphate metabolism in Italy, globally and for single different disorders 7. Clinical and biochemical characterization of different diseases of phosphate metabolism (according to single disorders and different genetic base), through both cross-sectional and longitudinal analyses of collected data 8. Evaluation of skeletal health and bone fragility in patients with diseases of phosphate metabolism, globally and based on single phosphate metabolism disorder, gender, and age 9. Self-evaluation of how the disease of phosphate metabolism interferes on the quality of life, daily activities, work, and emotional state of affected patients 10. Over time evaluation of responses to therapies in patients with diseases of phosphate metabolism.

3. Study population

The study will include a single cohort of female and male patients of any age, affected by a disease of phosphate metabolism.

The study does not include either any control group/comparison group or healthy volunteers.

Diseases of phosphate metabolism are classified as rare diseases and there are no data available on their true prevalence, as a whole. The prevalence of some specific phosphate metabolism disorders, such as X-linked hypophosphatemia (1-9/100,000), autosomal dominant hypophosphatemic rickets (\< 1/1,000,000), dominant hypophosphatemia with nephrolithiasis or osteoporosis (\< 1/1,000,000), is available on the Portal for Rare Diseases and Orphan Drugs (Orphanet). Based on the prevalence data available those single phosphate metabolism disorders on Orphanet we can estimate that a minimum of 100 patients will be globally collected in the present study.

3.1 Inclusion criteria

* Clinical and/or genetic diagnosis of a rare disease of phosphate metabolism 3.2 Exclusion criteria
* None

  4. Study design and setting

Non-profit, multicenter, national, retro-prospective, observational study, consisting in the design, creation, management and analysis of an Italian database of patients affected by diseases of phosphate metabolism.

The study will last 10 years. The enrollment of patients, the inclusion in the database with retrospective collection of their clinical data, and the subsequent prospective collection of clinical follow-up data will take place throughout the duration of the study. For the retrospective collection, retrospective data on the disease of phosphate metabolism will be retrieved from patient's medical records, at the time of the medical visit that the patient will carry out at the Clinical Center for the evaluation of his/her disease, regardless of inclusion in this study. Prospective data relating to the follow-up of disease of phosphate metabolism will be collected during the subsequent medical follow-up visits, scheduled for each patient as part of the clinical management of his/her clinical condition, regardless of inclusion in this study.

Being an observational study, this study itself does not involve the administration of any drug, nor the use of any medical device, nor does it involve additional medical visits, clinical analyses or care procedures in addition to those conventionally scheduled for the clinical and therapeutic management of patient affected by a disease of phosphate metabolism. No participant biospecimens of any type will be collected and retained to perform this study. Therapies for which data on response outcomes will be collected in the database, are those usually employed for the treatment of patients with diseases of phosphate metabolism, regardless of their inclusion in this observational study.

All data will be collected anonymously, and they will be analyzed as aggregates. Data collected in the database will be, first, processed using descriptive statistics, such as frequency tables for categorical data, median and quartiles for quantitative data on ordinal scales and mean and standard deviation for quantitative data on metric scales. Secondly, the correlations between variables will be evaluated using the Pearson correlation index in the case of continuous variables and the chi-square test for categorical variables.

5. Data and variables

Data collected in the database will include (if available in patient's medical records and part of the normal clinical and therapeutic management of patient regardless of inclusion in this study):

* Demographics (sex, year of birth)
* Age at diagnosis/onset of disease of phosphate metabolism
* Personal clinical history of disease of phosphate metabolism
* Family history of disease of phosphate metabolism in first-degree relatives
* Presence of comorbidities
* Result of the genetic testing for genes known to be involved in the development of congenital diseases of phosphate metabolism
* Clinical manifestations of the disease and related signs and symptoms
* Over time evaluation of biochemical parameters of metabolism of phosphate (i.e phosphatemia and 24h phosphaturia)
* Over time biochemical evaluation of kidney function (i.e. creatinine, clearance of creatinine, estimated glomerular filtration rate, spot proteinuria, 24h proteinuria)
* History of fragility fractures, bone deformities and altered musculoskeletal development
* Over time evaluation of biochemical parameters of calcium and bone metabolism (i.e calcemia, calcium ion, 24h calciuria, 25(OH)-vitamin D, 1,25(OH)2-vitamin D, parathyroid hormone, bone alkaline phosphatase, serum carboxy-terminal collagen crosslinks, serum procollagen 1 N-terminal propeptide)
* Over time skeletal X-ray analysis (absence/presence of vertebral fracture, osteomalacia, of calcinosis, not healing fractures, extra skeletal calcifications)
* Over time instrumental assessment of bone mineral density and bone tissue microstructure \[assessed by Dual-energy X-ray absorptiometry (DXA), Radiofrequency Echographic Multi Spectrometry (REMS), peripheral Quantitative Computed Tomography (pQCT), and/or High-Resolution pQCT (HR-pQCT)\]
* Self-evaluation of health-related quality of life through the 36-Item Short Form Health Survey (SF-36) questionnaire
* Pharmacological therapies (drug, duration, posology)
* Disease-related morbidity and mortality

Eligibility Criteria:
Inclusion Criteria:

* Clinical and/or genetic diagnosis of a rare disease of phosphate metabolism

Exclusion Criteria:

* None