Context
Fibrous dysplasia/McCune-Albright syndrome (FD/MAS) is a rare genetic disorder. Incidence and prevalence are not well-studied. Epidemiological research is complicated by the rarity of FD/MAS, absence of registries, heterogeneous presentation and possibly asymptomatic phenotype. FD/MAS may present with FGF23-mediated hypophosphatemia, of which the epidemiology is also unclear.
Objective
Evaluate incidence and prevalence of FD/MAS and FD/MAS-related hypophosphatemia.
Design
Cohort study based on nation-wide Danish registry from 1995-2018.
Setting
Population of Denmark.
Patients
Identified from the Danish National Patient Registry by ICD-10 codes M85.0 (monostotic FD, MFD) and Q78.1 (polyostotic FD(PFD)/MAS).
Main outcomes measures
Incidence rates and prevalence were calculated and stratified by sex, age, calendar period and diagnosis code. Cases were screened for FD-associated hypophosphatemia by diagnosis code ‘disorder of mineral metabolism’ (E.83) and dispatched vitamin D analogues. Measures were presented with 95% confidence intervals.
Results
408 patients were identified, 269 with MFD (66%), 139 with PFD/MAS (34%), comparable between sexes. Incidence of FD/MAS demonstrated increasing secular trend with a rate of 3.6 per 1,000,000 person years [95%CI 2.9,4.5] in 2015-2018. Incidence peaked between age 11-20. Prevalence of FD/MAS increased over time to 61.0 [95%CI 54.6,67.4] per 1,000,000 persons in 2018. Incidence rate of MFD was 1.5-fold of PFD/MAS in the first decade, rising to 2.5-fold in the last decade. No FD/MAS cases were registered with diagnosis code or treatment for hypophosphatemia.
Conclusions
FD/MAS is rare, diagnosis peaks during adolescence without sex predominance, MFD is most prevalent. Hypophosphatemia may be underdiagnosed and undertreated, or underregistered, comparing this study to literature.