Prevalence and risk factors for kidney stones in fibrodysplasia ossificans progressiva.

The worldwide prevalence and risk factors for kidney stones in patients with fibrodysplasia ossificans progressiva (FOP) are unknown. We conducted a survey of 383 patient-members of the International Fibrodysplasia Ossificans Progressiva Association, comprising the entire global membership of the international FOP community. Two hundred seven patients from 31 nations and 6 continents (54%) responded. Nineteen of 207 respondents had kidney stones, revealing a worldwide prevalence of 9.2%. In a confirmatory follow-up study of subjects participating in a longitudinal FOP natural history study, 9 of 114 individuals reported a history of kidney stones (7.9%). In both study populations patients with kidney stones were found to be more functionally impaired compared to those without nephrolithiasis. The prevalence of kidney stones in the adult FOP population of the Unites States was 15.8% (9/57 individuals) compared to a sex- and age-weighted prevalence of 4.5% (p=4×10-5) in the general population. Although geographical variation exists, patients with FOP have an approximately three-fold greater prevalence of kidney stones than the general population. This unusually high prevalence may be due to high bone turnover from chronic immobilization, or to unknown mechanistic effects of the activating FOP mutation in activin A receptor, type I/activin-like kinase-2 (ACVR1/ALK2), increasing the disease burden and morbidity in this already disabling condition.