Final answer:
The EMG would likely reveal myopathic changes indicative of Duchenne muscular dystrophy, a genetic disorder caused by mutations in the dystrophin gene, leading to progressive muscle weakness and calf pseudohypertrophy.
Step-by-step explanation:
The description provided suggests a classic case of Duchenne muscular dystrophy (DMD), a genetic disorder characterized by progressive muscle degeneration and weakness. Given the symptoms described, such as a four-point gait when rising from the ground (Gower's sign), waddling gait, calf pseudohypertrophy, and proximal muscle weakness, an EMG would likely reveal myopathic changes. These changes are indicative of a primary muscle disease rather than a nerve disorder and would be characterized by short, small, abundant, polyphasic motor unit action potentials.
The genetic mutation responsible for DMD occurs in the gene that encodes for the protein dystrophin, which is crucial for muscle fiber integrity. The loss of dystrophin leads to muscle cell damage and the clinical symptoms observed. A confirmatory genetic test could reveal mutations such as deletions or duplications in the dystrophin gene located on the X chromosome.