A 12-year-old boy with severe deafness has a long QT interval on ECG. What is the likely genetic mutation in this patient?

• A. a-Adrenergic receptor
• B. b-Adrenergic receptor
• C. Voltage-gated potassium channel
• D. Gap junction channel

Answer: (C)

In this case, the combination of severe deafness and a long QT interval on the ECG suggests a genetic condition known as Jervell and Lange-Nielsen syndrome. This syndrome is characterized by congenital, profound sensorineural hearing loss and a prolonged QT interval, which can lead to life-threatening arrhythmias.

The underlying cause of Jervell and Lange-Nielsen syndrome is primarily due to mutations in genes that encode for voltage-gated potassium channels, particularly the KCNQ1 (also known as Kv7.1) and KCNE1 genes. These potassium channels are crucial for cardiac repolarization, and mutations can disrupt the normal electrical activity of the heart, leading to the observed long QT intervals.

Additionally, the involvement of these potassium channels explains not just the cardiac symptoms, but they are also implicated in the auditory system leading to the hearing loss seen in affected individuals. Thus, the presence of both severe deafness and a long QT interval indicates a genetic mutation affecting the voltage-gated potassium channels.