Pseudoxanthoma elasticum (PXE) is a rare genetic disorder characterized by ectopic calcifications in the skin, retina and arterial walls. Angers University Hospital is the national rare disease reference center (CRMR) for PXE. Although PXE is hereditary, its main clinical manifestations (unsightly skin lesions, intermittent arterial claudication, stroke, retinal bleeding and blindness) are delayed and slowly progress over the course of a lifetime. They are rarely life-threatening but have a major functional impact. To date, management of PXE is purely preventive and symptomatic. Three successive "states" can be individualized during PXE course, corresponding to three very different patient profiles in terms of age, clinical manifestations, occurrence of complications and their treatment.

PXE is essentially a severe disease in adults in the second half of life. This contrasts with the presence of many patients seen for their follow-up at school age or in employment, and at the age of children. It is therefore necessary to optimize the recruitment of PXE patients and to rethink their follow-up by the CRMR.

The investigators hypothesize that the implementation of alternating treatment paths, better adapted to each of the three patient profiles, including multidisciplinary teleconsultations, will not only increase the number of patients monitored by the CRMR and benefit from referral care, but also to optimize care, for greater patient satisfaction, their local doctors and the CRMR team.

This is a quasi-experimental study evaluating the impact of new support modalities according to a before/after design with an intermediate transition period of 2 years necessary for the proper deployment of these new modalities. The study includes 3 separate periods of 2 years from its implementation:

• Period A1-2: continuation of the recruitment, monitoring and care methods for PXE patients as they are currently carried out. This period will allow the collection of baseline evaluation criteria
• Period A3-4 (intermediate period without evaluation/monitoring of indicators): gradual implementation of the internal organizational changes necessary for the deployment of alternating pathways.
• Period A5-6 (second period of interest for the evaluation of indicators): evaluation of fully operational alternating pathways for the recruitment, monitoring and care of PXE patients. This period will allow the collection of evaluation criteria and comparison with those of baseline).

For the main objective and the first secondary objectives relating to the optimization of the care pathway, the analysis will be carried out using global activity data at the CRMR level (non-identifying aggregated data).

This research involving humans is qualified as non-interventional research because to respond to :

• the second secondary objective about 'Evaluation of the impact of alternating courses adapted to age and clinical symptoms on the following criteria', patients will answer questionnaires specific to the study (quality of life, satisfaction and confidence for the patient and the treating physicians involved)
• the third secondary objective, semi-directed interviews will be carried out for patients, relatives (except parents) and treating physicians who agree to participate in the qualitative sub-study.

The overall activity data of the CRMR will be collected retrospectively and prospectively on the basis of all source data in order to characterize the evolution of the active file in terms of patients "duly followed up", "contacts without follow-up" or "lost to follow-up" during periods A1-A2 and A5-A6.

Inclusion Criteria:

• For the main objective and the first secondary objectives : The population taken into account corresponds to all the support and requests managed by the CRMR over the periods of interest (period A1-2 and period A5-6).
• Inclusion in REMOTE-PXE is offered to any patient with a PXE, defined phenotypically or genotypically (see below), treated at the CRMR during the periods of interest. Note that inclusions are independent between the 2 periods (a patient included during period A1-2 can be included again if he/she is treated during period A5-6). PXE is defined phenotypically:
• by the presence of specific skin lesions (clinically suggestive and showing dermal elastorrhexis on skin biopsy) in patients under 25 years of age
• OR by the combination of specific skin lesions (clinically suggestive and showing dermal elastorrhexis on skin biopsy) and specific ophthalmologic lesions, complicated or not (depending on age: orange peel, angioid streaks, retinal dystrophy) over 25 years of age PXE is defined genotypically, regardless of the patient's age, by the identification of two variants in the ABCC6 gene.
• Participation in the qualitative study (semi-directed interviews) will be offered to a sample of patients included in the RIPH during the A5-A6 period among patients who were already followed before the A3-A4 period since the objective is to collect their experiences and perceptions of this reorganization of care. Only patients agreeing to participate in this sub-study and giving their consent for the recording of the interviews will be included.

Exclusion Criteria:

• Person objecting to participating in the research
• Patient under curatorship, guardianship and legal protection

Patients belonging to the CRMR active cohort will be defined by:

• for new patients: patients for whom CRMR care has been provided, i.e. a stay at the CRMR (consultation or hospitalization) or a teleconsultation with the CRMR team) was provided within a maximum of 3 months after an initial contact made during the period of interest
• for patients already in the CRMR active file (patients who have benefited from at least one care in the last 5 years): patients for whom the CRMR care provided for the period, i.e. a stay at the CRMR (consultation or hospitalization) or a teleconsultation with the CRMR multidisciplinary team, was provided in accordance with the planned frequency with a tolerance window of 6 months.