SNP Shot: Genomic Insights

Sick sinus syndrome, also known as sinus node dysfunction, encompasses a range of heart conditions that affect the heart's rhythm. The term "sick sinus" refers to the sinoatrial (SA) node, a cluster of specialized cells within the heart that serves as its natural pacemaker. The SA node generates electrical impulses, initiating each heartbeat. These impulses travel from the SA node to the rest of the heart, signaling the cardiac muscle to contract and pump blood. In individuals with sick sinus syndrome, the SA node malfunctions. This can manifest as the SA node failing to generate appropriate signals for a regular heartbeat, or as abnormalities disrupting the electrical impulses and preventing them from effectively reaching other parts of the heart.

A common characteristic of sick sinus syndrome is an abnormally slow heartbeat (bradycardia), although occasionally the heartbeat can be too fast (tachycardia). Some individuals experience rapid shifts between excessively fast and excessively slow heartbeats, a condition known as tachycardia-bradycardia syndrome. Symptoms associated with these irregular heartbeats can include dizziness, lightheadedness, fainting (syncope), a fluttering or pounding sensation in the chest (palpitations), and confusion or memory problems. Many affected individuals experience chest pain, shortness of breath, or excessive tiredness (fatigue) during physical activity. Once symptoms of sick sinus syndrome manifest, they generally worsen over time. However, some individuals with the condition remain asymptomatic throughout their lives.

Sick sinus syndrome is most prevalent among older adults but can occur in individuals of any age. The condition elevates the risk of several serious cardiovascular complications, including atrial fibrillation, heart failure, cardiac arrest, and stroke.

Inheritance:

The majority of sick sinus syndrome cases are not inherited and are considered sporadic. Sporadic cases arise in individuals without a family history of the disorder. In cases where sick sinus syndrome results from mutations in the HCN4 gene, it follows an autosomal dominant inheritance pattern. This means that only one copy of the mutated gene in each cell is sufficient to cause the condition. Typically, an affected individual will have one parent who also has the condition. Conversely, when sick sinus syndrome is caused by mutations in the SCN5A gene, it is inherited in an autosomal recessive manner. This means that both copies of the gene in each cell must be mutated for the condition to manifest. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene but usually do not exhibit signs or symptoms of the condition themselves.