ATFB9; HHBIRK1; HHIRK1; IRK1; Kir2.1; LQT7; SQT3
The KCNJ2 gene is associated with autosomal dominant Andersen-Tawil syndrome, also known as long QT syndrome (LQTS), type 7 (MedGen UID: 327586), short QT syndrome (SQTS) (MedGen UID: 400662), and catecholaminergic polymorphic ventricular tachycardia (CPVT) (PMID: 22589293). Additionally, the KCNJ2 gene has preliminary evidence supporting a correlation with autosomal dominant atrial fibrillation (MedGen UID: 462781).
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Pathogenic KCNJ2 variants are associated with ~60% of clinical cases of Andersen-Tawil syndrome, a subtype of LQTS. Overall, KCNJ2 is associated with an unknown percentage of clinical cases of LQTS. KCNJ2 is also a rare cause of SQTS and causes an unknown percentage of CPVT and atrial fibrillation cases.
The KCNJ2 gene encodes the potassium inwardly-rectifying channel, subfamily J, member 2. The electrical activity of muscle is controlled by the movement of potassium, sodium, and calcium ions across the cardiac muscle cells. Pathogenic variants in genes that encode potassium channels or subunits are a common cause of inherited cardiac arrhythmias.
The KCNJ2 gene is associated with Andersen-Tawil syndrome (also known as long QT syndrome [LQTS] type 7), short QT syndrome (SQTS), and catecholaminergic polymorphic ventricular tachycardia (CPVT). Additionally, preliminary evidence also supports a correlation between the KCNJ2 gene and autosomal dominant atrial fibrillation (AFib; PMID: 23684683, 19862833, 21787999).
Andersen-Tawil syndrome (ATS) is a multisystem disorder that primarily involves periodic paralysis (episodic muscle weakness), cardiac arrhythmias, and dysmorphic features. The cardiac arrhythmias are ventricular and may also show prolonged QTc and enlarged U wave on electrocardiogram (ECG/EKG). These arrhythmias can result in recurrent syncope, seizure-like activity, or sudden cardiac arrest/death. Individuals with ATS usually also have a combination of physical findings that can include low-set ears, widely spaced eyes, small lower jaw, curving of the pinky finger (fifth-digit clinodactyly), webbed fingers (syndactyly), short stature, and scoliosis (MedGen UID: 327586; GeneReviews. Andersen-Tawil syndrome. https://www.ncbi.nlm.nih.gov/books/NBK1264/. Accessed June 2017).
LQTS, SQTS, and CPVT are cardiac arrhythmia conditions that primarily affects the electrical system of the heart.
The abnormal heart beats in these arrhythmia conditions can lead to palpitations, dizziness (pre syncope), fainting (syncope), seizure-like activity, and in some cases, sudden cardiac arrest/death, including sudden infant death syndrome (SIDS). Symptoms can present in both children and adults and may be triggered by exercise, acute emotion, homeostatic imbalance, and use of certain medications (PMID: 24093767).
AFib is a cardiac arrhythmia characterized by rapid, chaotic beats originating from the top chambers of the heart. Symptoms may include shortness of breath, palpitations, and weakness, along with an increased risk for cardiomyopathy, heart failure, or stroke (MedGen UID: 462781; PMID: 25215263).
The KCNJ2 gene encodes the inwardly rectifying potassium channel, subfamily J, member 2 (Kir2.1), which plays a key role in a cell’s ability to generate and transmit electrical signals. The Kir2.1 protein forms ion channels that are active in skeletal and cardiac muscle. In skeletal muscle, the channels aid in the muscle contraction and relaxation that drive physical movement. In the heart, the channels help recharge the cardiac muscle after each heartbeat to maintain normal heart rhythm. Additionally, a role for KCNJ2-derived channels in bone development has been suggested but is less clear. These channels are activated by a molecule PIP2, whose binding is required for normal channel function (National Library of Medicine. Genetics Home Reference. KCNJ2 gene. https://ghr.nlm.nih.gov/gene/KCNJ2. Accessed June 2017; PMID: 17221872, 23684683).
Pathogenic variants in KCNJ2 have autosomal dominant inheritance. This means that an individual with a pathogenic variant has a 50% chance of passing it to their offspring. Pathogenic KCNJ2 variants can be inherited or occur de novo. Clinically, these variants exhibit reduced penetrance and variable expression (PMID: 12163457, 22589293).
Approximately 60% of individuals with ATS will have all three of the major ATS features (i.e., periodic paralysis, cardiac arrhythmias, and physical findings), while 80% of individuals with ATS will have at least two of the three major features (PMID: 12163457).
ATS is managed symptomatically with oral potassium and/or diet and lifestyle modifications for episodic weakness. Arrhythmias, present with or without the other feature of ATS, are managed depending on clinical presentation, with options including lifestyle modification, medication, surgery, and device therapy (PMID: 24093767).
Review date: June 2017
Invitae is a College of American Pathologists (CAP)-accredited and Clinical Laboratory Improvement Amendments (CLIA)-certified clinical diagnostic laboratory performing full-gene sequencing and deletion/duplication analysis using next-generation sequencing technology (NGS).
Our sequence analysis covers clinically important regions of each gene, including coding exons, +/- 10 base pairs of adjacent intronic sequence, and select noncoding variants. Our assay provides a Q30 quality-adjusted mean coverage depth of 350x (50x minimum, or supplemented with additional analysis). Variants classified as pathogenic or likely pathogenic are confirmed with orthogonal methods, except individual variants that have high quality scores and previously validated in at least ten unrelated samples.
Our analysis detects most intragenic deletions and duplications at single exon resolution. However, in rare situations, single-exon copy number events may not be analyzed due to inherent sequence properties or isolated reduction in data quality. If you are requesting the detection of a specific single-exon copy number variation, please contact Client Services before placing your order.
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