PURPOSE: To assess the incidence of Stargardt disease (STGD1) and to evaluate demographics of incident cases.
METHODS: For this retrospective cohort study, demographic, clinical and genetic data of patients with a clinical diagnosis of STGD1 were registered between September 2010 and January 2020 in a nationwide disease registry. Annual incidence (2014-2018) and point prevalence (2018) were assessed on the basis of this registry.
RESULTS: A total of 800 patients were registered, 56% were female and 83% were of European ancestry. The incidence was 1.67-1.95:1,000,000 per year and the point prevalence in 2018 was approximately 1:22,000-1:19,000 (with and without 10% of potentially unregistered cases). Age at onset was associated with sex (p = 0.027, Fisher's exact); 1.9x more women than men were observed (140 versus 74) amongst patients with an age at onset between 10 and 19 years, while the sex ratio in other age-at-onset categories approximated one. Late-onset STGD1 (≥45 years) constituted 33% of the diagnoses in 2014-2018 compared to 19% in 2004-2008. Diagnostic delay (≥2 years between the first documentation of macular abnormalities and diagnosis) was associated with older age of onset (p = 0.001, Mann-Whitney). Misdiagnosis for age-related macular degeneration (22%) and incidental STGD1 findings (14%) was common in patients with late-onset STGD1.
CONCLUSION: The observed prevalence of STGD1 in real-world data was lower than expected on the basis of population ABCA4 allele frequencies. Late-onset STGD1 was more frequently diagnosed in recent years, likely due to higher awareness of its phenotype. In this pretherapeutic era, mis- and underdiagnosis of especially late-onset STGD1 and the role of sex in STGD1 should receive special attention.