Which genetic condition is primarily indicated by the finding of a telephone receiver femur in an ultrasound?

The finding of a telephone receiver femur during an ultrasound is a classic characteristic associated with thanatophoric dysplasia type 1. This genetic condition is not only characterized by this specific skeletal anomaly but also includes other features such as severe short stature, a narrow chest, and a disproportionately large head with frontal bossing. The abnormal curvature of the femur that resembles a telephone receiver is significant in prenatal imaging and is critical in supporting a diagnosis of thanatophoric dysplasia.

Other conditions listed do not present with this classic radiological finding. For instance, Tuberous Sclerosis Complex (TSC) is primarily associated with hamartomas and other systemic manifestations rather than specific skeletal malformations. Holt-Oram syndrome is characterized by heart defects and upper limb anomalies, with no typical skeletal features such as the telephone receiver femur. Beckwith-Wiedemann syndrome, though it presents with a range of embryonal tumors and overgrowth, does not have skeletal anomalies as a defining feature. Thus, thanatophoric dysplasia type 1 is the only condition among the choices that is directly indicated by the telephone receiver femur finding.