Retrospective study of foramen magnum development in patients with achondroplasia starting vosoritide before age 3

Achondroplasia (ACH) is a monogenic skeletal dysplasia caused by gain-of-function variants in FGFR3, leading to impaired endochondral ossification and foramen magnum stenosis. Although vosoritide promotes endochondral ossification, its effects on foramen magnum development remain unclear. In this study, we evaluated the impact of early vosoritide administration on foramen magnum development in infants and young children with ACH, using longitudinal magnetic resonance imaging.

This retrospective, single-center case series included 9 patients who initiated vosoritide before age 3 years. Serial head magnetic resonance imaging scans were analyzed. The anteroposterior and transverse diameters of the foramen magnum were measured and compared with reference curves from untreated ACH cohorts. The severity of stenosis was assessed using the ACH foramen magnum score (AFMS). Correlations between changes in body height standard deviation score and foramen magnum dimensions were assessed.

Vosoritide was initiated at a median age of 4 months, with a mean treatment duration of 2.5 years. Compared with untreated cohorts, steeper growth rates were observed in 8 of the 9 patients for the anteroposterior diameter and in all patients for the transverse diameter. Most patients remained at AFMS 1 or 2. One patient progressed to AFMS 3 and underwent decompression surgery at age 11 months. No significant correlation was identified between changes in body height standard deviation score and foramen magnum diameter.

Early vosoritide administration may promote foramen magnum development in infants and young children with ACH, independently of systemic growth effects. Even when height improvement is limited, enhancement of foramen magnum growth may be clinically relevant.