Fibrodysplasia Ossificans Progressiva (FOP)
An extremely rare genetic condition (approximately 1 in 2 million) where soft tissues progressively turn into bone. Palovarotene, a retinoic acid receptor gamma agonist (not a peptide itself but tracked on PeptideTrace), is approved for FOP in certain populations.
Technical Context
FOP is an ultra-rare autosomal dominant disorder (prevalence approximately 1:1.36 million) caused by a gain-of-function mutation in ACVR1 (activin A receptor type 1, also called ALK2) — the R206H mutation accounts for approximately 97% of cases. ACVR1 is a BMP type I receptor; the mutation causes constitutive activation and aberrant response to activin A (which normally does not activate ACVR1) → ectopic endochondral ossification in soft tissues (muscle, tendons, ligaments, fascia). Hallmark: progressive heterotopic ossification forming a 'second skeleton' that immobilises joints. Clinical course: episodic flare-ups (often triggered by trauma, surgery, or intramuscular injections) leading to cumulative disability. Palovarotene (Sohonos): retinoic acid receptor gamma (RARγ) agonist that inhibits BMP-dependent chondrogenesis — blocking the endochondral ossification pathway downstream of aberrant ACVR1 signalling. FDA approved 2023 for FOP in adults and children ≥8 years (females) or ≥10 years (males), with growth plate monitoring required due to premature epiphyseal closure risk.