HCN4

At least five mutations in the HCN4 gene have been identified in people with sick sinus syndrome, a heart condition that affects the function of the SA node. Most of these mutations change single protein building blocks (amino acids) in the HCN4 channel. In some cases, fewer of the altered channels reach the cell membrane, where they are needed to transport ions. In other cases, the channel is in the right place but has an abnormal structure that changes how ions flow through it. All of the mutations reduce the overall flow of ions into cells of the SA node, preventing it from creating the electrical signals that control the heartbeat. These changes increase the risk of an abnormally slow heartbeat (bradycardia), which can cause dizziness, light-headedness, fainting (syncope), and related symptoms. HCN4 gene mutations have also been found in people who have a slow heartbeat without any other symptoms (asymptomatic bradycardia).

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