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Background Although congenital adrenal hyperplasia (CAH) is known to be associated with adrenal crises (AC), its association with patient or clinician reported sick day episodes (SDE) is less clear. Methods Data on children with classic 21-hydroxylase deficiency CAH from 34 centers in 18 countries, of which 7 were Low or Middle Income (LMIC) and 11 were High Income (HIC), were collected from the International CAH Registry and analysed to examine the clinical factors associated with SDE and AC. Results 518 children with a median of 11 children (range 1, 53) per center had 5,388 visits evaluated over a total of 2,300 patient years. The median number of AC and SDE per patient year per center was 0 (0, 3) and 0.4 (0.0, 13.3), respectively. Of the 1,544 SDE, an AC was reported in 62 (4%), with no fatalities. Infectious illness was the most frequent precipitating event, reported in 1,105 (72%) and 29 (47%) of SDE and AC, respectively. On comparing cases from LMIC and HIC, the median SDE per patient year was 0.75 (0, 13.3) vs 0.11 (0, 12.0) (p<0.001), respectively and the median AC per patient year was 0 (0, 2.2) vs 0 (0, 3.0) (p=0.43), respectively. Conclusions The real-world data that are collected within the I-CAH Registry show wide variability in the reported occurrence of adrenal insufficiency related adverse events. As these data become increasingly used as a clinical benchmark in CAH care, there is a need for further research to improve and standardise the definition of SDE.

Rare disease (RD) registries are important platforms that facilitate communication between health care professionals, patients and other members of the multidisciplinary team. RD registries enable data sharing and promotion of research and audits, often in an international setting, with the overall aim of improving patient care. RD registries also have a fundamental role in supporting the work of clinical networks such as the European Reference Networks (ERNs) for rare diseases. With the recent expansion of RD registries, it has become even more essential to outline standards of good practice in relation to governance, infrastructure, documentation, training, audits and adopting the Findable, Accessible, Interoperable and Reusable (FAIR) data principles to maintain registries of high quality. For the purpose of this paper, we highlight vital aspects of data access and data governance policies for RD registries, using the European Registries for Rare Endocrine Conditions (EuRRECa) as an example of a project that aims to promote good standards of practice for improving the quality of utilization of RD registries.

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