Atypical Phenotypic Presentation of Achondroplasia with Radial Ray Anomaly: A Case Report

Abstract Achondroplasia is the most common nonlethal skeletal dysplasia and is characterized by rhizomelic limb shortening, macrocephaly, and typical craniofacial features. Prenatal diagnosis may be challenging, particularly when atypical phenotypic features overlap with other skeletal dysplasias. Radial ray anomalies are exceedingly rare in association with achondroplasia. We report a rare prenatal case of atypical achondroplasia with unilateral radial ray anomaly and fetal edema. A 21-year-old primigravida underwent her first anomaly scan at 20 weeks and 5 days of gestation. Ultrasound demonstrated a single live fetus with bilateral bowed femora (< 3 standard deviation [SD]), shortened tibiae (< 2 SD), shortened humeri and ulnae (< 2 SD), and a right short radius. The left radius was severely shortened (< 3 SD) and dysplastic with an absent thumb, consistent with a radial ray anomaly. A widened trident hand was noted on the right. Additional findings included diffuse fetal head edema, raised nuchal fold thickness, a depressed nasal bridge, and an abnormal cavum septum pellucidi. Thoracic measurements and abdominal organs were normal. Amniocentesis and whole-exome sequencing identified a pathogenic p.Gly380Arg mutation in the FGFR3 gene, confirming the diagnosis of achondroplasia. Given the atypical features and potential severity, the couple opted for pregnancy termination. This case expands the phenotypic spectrum of achondroplasia, highlighting a rare association with radial ray anomaly and fetal edema. Accurate prenatal diagnosis requires integration of detailed ultrasonographic findings with genetic analysis, especially in atypical skeletal dysplasias. Early diagnosis facilitates informed counseling and appropriate pregnancy management.