A 12-year-old boy with consanguineous parents from Central Asia presents with progressive bilateral sensorineural hearing loss first noticed at age 8. Pure tone audiometry shows mild loss at 250 Hz, moderate loss at 500–2000 Hz, and severe loss at 4000–8000 Hz. The severely affected high-frequency air conduction thresholds at 4000–8000 Hz creating a downsloping configuration (marked **C** in the diagram) are characteristic of which genetic condition?