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Pediatrics - Cardiology

Houston, Texas

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Pediatrics - Cardiology
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KCNJ8 Mutation Analysis

KCNJ8 gene contains three exons (1 noncoding) spanning 10.6 kb of genomic distance that has been mapped to chromosome 12p12.1. The protein encoded by this gene is an integral membrane protein of inward-rectifier type potassium channels. The channels are characterized by a greater tendency to allow potassium to flow into a cell rather than out of a cell. This potassium channel is controlled by G proteins. Their voltage dependence is regulated by the concentration of extracellular potassium; as external potassium is raised, the voltage range of the channel opening shifts to more positive voltages. The inward rectification is mainly due to the blockage of outward current by internal magnesium. Mutations in this gene are associated with Brugada syndrome, J-wave syndromes and sudden infant death syndrome (SIDS). KCNJ8 mutations demonstrate autosomal dominant inheritance with a broad range of clinical severity both within and between families.

The John Welsh Cardiovascular Diagnostic Laboratory offers molecular genetic testing for KCNJ8 mutations. Individuals are tested by automatic fluorescent DNA sequencing of the coding exons of the KCNJ8 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 sudden infant death syndrome (SIDS) and J-wave syndromes.

Methodology

Genomic DNA is analyzed for KCNJ8 mutations by automatic fluorescent DNA sequencing of the coding exons of the KCNJ8 gene, as well as the exon/intron junctions and a portion of the 5' and 3' untranslated regions. 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) $600 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 2-3 of KCNJ8.

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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