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Pediatrics - Cardiology

Houston, Texas

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Pediatrics - Cardiology
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KCND3 Mutation Analysis

KCND3 is a member of the potassium channel, voltage-gated, shal-related subfamily. The members of this subfamily form voltage-activated A-type potassium ion channels and are prominent in the repolarization phase of the action potential. KCND3 contains 6 transmembrane segments and intracellular N- and C-termini. KCND3 has two isoforms, which are encoded by alternatively spliced transcript variants of the KCND3 gene located at chromosome 1p13.2. Only the long form of KCND3 is expressed in the heart. The long form of the KCND3 gene contains 7 exons and spans more than 25-kb genomic interval. The shorter isoform is encoded by 6 exons. The transient outward potassium current, I(to), is especially important during the early phase of repolarization, as it sets the plateau voltage of both the atrial and the ventricular action potential. KCND2 and/or KCND3 code for the primary alpha subunits responsible for I(to). It has been reported that KCND3 gain-of-function mutations can lead to Brugada syndrome, characterized by ST-segment elevation in the right precordial leads and sudden death due to ventricular tachycardia/ventricular fibrillation in the absence of structural heart disease. Definitive genotype/phenotype correlations have not been described.

The John Welsh Cardiovascular Diagnostic Laboratory offers molecular genetic testing for KCND3 mutations. Individuals are tested by automatic fluorescent DNA sequencing of the coding exons of the KCND3 gene. We strongly recommend initial testing of a clearly affected individual, if available, in order to provide the greatest test sensitivity and clearest interpretation of results for subsequent family members. Genetic counseling is recommended for all individuals.

Reasons for Referral

Molecular confirmation of the diagnosis of Brugada syndrome.

Methodology

Genomic DNA is analyzed for KCND3 mutations by automatic fluorescent DNA sequencing of the coding exons of the KCND3 gene, as well as the exon/intron junctions and a portion of the 5' and 3' untranslated region. Patient DNA is sequenced in both the forward and reverse orientations. If a mutation is identified, additional family members are analyzed only for the familial mutation by automatic fluorescent DNA sequencing.

Service Fees

Service Direct and Institutional Billing CPT Codes
Index Case (Full Gene) $800 per sample 81404, G0452
Additional Family Members $300 per sample; known familial mutation only 81403, G0452

Sensitivity

DNA Sequencing Analysis: Approximately 99 percent detection of mutations in coding exons 1-7 of KCND3.

Specimen Requirements

Blood (preferred): EDTA (purple-top) tubes: Adult: 5 cc, Child: 5 cc, Infant: 2-3 cc
Tissue: Frozen (preferred), RNAlater, Formalin-fixed, Paraffin-embedded
Other Body Fluids: Call to inquire
Buccal Swabs: One swab from each cheek

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