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Loss-of-function mutations in the KCNJ8-encoded Kir6.1 K(ATP) channel and sudden infant death syndrome
David J Tester1, Bi-Hua Tan, Argelia Medeiros-Domingo
1Department of Medicine, Division of Cardiovascular Diseases, Windland Smith Rice Sudden Death Genomics Laboratory, Mayo Clinic, Rochester, MN 55905, USA.
Insights
Sudden infant death syndrome (SIDS) may be linked to KCNJ8 gene mutations affecting cardiac function. Researchers identified two novel loss-of-function mutations in SIDS cases, suggesting a new cause for SIDS.
Area of Science:
- Cardiovascular Genetics
- Pediatric Pathology
- Molecular Biology
Background:
- Cardiac channelopathies are implicated in approximately 10% of sudden infant death syndrome (SIDS) cases.
- The KCNJ8-encoded Kir6.1 (K(ATP)) channel is crucial for vascular tone and cardiac adaptation to metabolic stress.
- KCNJ8-deficient mice exhibit premature death, especially with infection, highlighting the gene's importance.
Purpose of the Study:
- To investigate the spectrum, prevalence, and functional impact of KCNJ8 mutations in a large cohort of SIDS cases.
- To identify novel KCNJ8 mutations associated with SIDS and characterize their functional consequences.
Main Methods:
- Comprehensive mutational analysis of the KCNJ8 gene (open reading frame/splice-site) in 292 SIDS cases using PCR, DHPLC, and DNA sequencing.
- Heterologous coexpression of identified KCNJ8 mutations with SUR2A in COS-1 cells.
- Functional characterization using whole-cell patch-clamp electrophysiology to assess K(ATP) channel activity.
Main Results:
- Two novel KCNJ8 mutations, E332del and V346I, were identified in two unrelated SIDS cases.
- Both mutations were located in the Kir6.1 C-terminus, involved conserved residues, and were absent in control populations.
- Functional analysis revealed that both mutations resulted in a significant decrease in K(ATP) current (40-68%) compared to wild-type.
Conclusions:
- Loss-of-function KCNJ8 mutations represent a novel pathogenic mechanism contributing to SIDS.
- These mutations may predispose infants to maladaptive cardiac responses during systemic metabolic stressors.
- Findings align with observations in KCNJ8-deficient mouse models, suggesting a conserved role in cardiac health.
Background:
Approximately 10% of sudden infant death syndrome (SIDS) may stem from cardiac channelopathies. The KCNJ8-encoded Kir6.1 (K(ATP)) channel critically regulates vascular tone and cardiac adaptive response to systemic metabolic stressors, including sepsis. KCNJ8-deficient mice are prone to premature sudden death, particularly with infection. We determined the spectrum, prevalence, and function of KCNJ8 mutations in a large SIDS cohort.
Methods And Results:
Using polymerase chain reaction, denaturing high-performance liquid chromatography, and DNA sequencing, comprehensive open reading frame/splice-site mutational analysis of KCNJ8 was performed on genomic DNA isolated from necropsy tissue on 292 unrelated SIDS cases (178 males, 204 white; age, 2.9±1.9 months). KCNJ8 mutations were coexpressed heterologously with SUR2A in COS-1 cells and characterized using whole-cell patch-clamp. Two novel KCNJ8 mutations were identified. A 5-month-old white male had an in-frame deletion (E332del) and a 2-month-old black female had a missense mutation (V346I). Both mutations localized to Kir6.1's C-terminus, involved conserved residues and were absent in 400 and 200 ethnic-matched reference alleles respectively. Both cases were negative for mutations in established channelopathic genes. Compared with WT, the pinacidil-activated K(ATP) current was decreased 45% to 68% for Kir6.1-E332del and 40% to 57% for V346I between -20 mV and 40 mV.
Conclusions:
Molecular and functional evidence implicated loss-of-function KCNJ8 mutations as a novel pathogenic mechanism in SIDS, possibly by predisposition of a maladaptive cardiac response to systemic metabolic stressors akin to the mouse models of KCNJ8 deficiency.
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