(Circulation. 2001;104:3030.)
© 2001 American Heart Association, Inc.
Brief Rapid Communications |
From the Section of Cardiology, Baylor College of Medicine, Houston, Tex.
Correspondence to Robert Roberts, MD, Don W. Chapman Professor of Medicine, Professor of Medicine and Cell Biology, Department of Medicine, Section of Cardiology, 6550 Fannin, MS SM677, Baylor College of Medicine, Houston, TX 77030. E-mail rroberts{at}bcm.tmc.edu
| Abstract |
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Methods and Results DNA was extracted from white blood cells obtained from family members. PRKAG2 exons were amplified by polymerase chain reaction and were screened for mutations by direct sequencing. The genomic organization of the PRKAG2 gene was determined using inter-exon long-range polymerase chain reaction for cDNA sequence not available in the genome database. A missense mutation, Arg531Gly, was identified in all affected individuals but was absent in 150 unrelated individuals. The PRKAG2 gene was determined to consist of 16 exons and is at least 280 kb in size.
Conclusions We identified a novel mutation (Arg531Gly) in the
-2 regulatory subunit (PRKAG2) of AMP-activated protein kinase (AMPK) to be responsible for a syndrome associated with ventricular preexcitation and early onset of atrial fibrillation and conduction disease. These observations confirm an important functional role of AMPK in the regulation of ion channels specific to cardiac tissue. The identification of the cardiac ion channel(s) serving as substrate for AMPK not only would provide insight into the molecular basis of atrial fibrillation and heart block but also may suggest targets for the development of more specific therapy for these common rhythm disturbances.
Key Words: Wolff-Parkinson-White syndrome genetics hypertrophy arrhythmia
| Introduction |
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-2 regulatory subunit (PRKAG2) of AMP-activated protein kinase (AMPK). Paroxysmal atrial fibrillation was particularly frequent, and chronic atrial fibrillation was present in 80% of patients >50 years of age.
See p 3014
We now report a third, unrelated family, which also has ventricular preexcitation, atrial fibrillation, and conduction defects. The third family has more severe disease, with onset in childhood instead of adolescence. No cardiac hypertrophy is present. DNA analysis of the third family shows the defect to be a novel mutation in PRKAG2. These results also emphasize that AMPK plays a significant role in cardiac development and ion channel regulation.
| Methods |
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wave). Conduction system disease was diagnosed if evidence of sinus node dysfunction or atrioventricular block was demonstrated on ECG. Twelve-lead ECGs were retrieved from archived medical records when possible.
Mutation Detection and Analysis
Exon-intron boundaries of the protein-encoding sequences of PRKAG2 were identified in the GenBank database, as previously described.5 For protein-encoding sequences (base pairs 205 to 556) not available by the sequence sampling approach, primers were designed from cDNA sequences and inter-exon long-range polymerase chain reaction (PCR) (Elongase, GIBCO) was used to determine exon-intron boundaries. Intronic primers were designed on the basis of exon-intron boundaries. Genomic DNA fragments were amplified by PCR, and the products were purified using the QIAquick PCR purification kit (QIAGEN). Direct sequencing reactions were performed in both the sense and antisense directions on an ABI PRISM 377 (Perkin-Elmer Applied Biosystems) using big dye chemistry.
| Results |
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Genomic Structure of the PRKAG2 Gene
We determined that the PRKAG2 cDNA sequence extending from base pairs 205 to 556 encode 2 exons, exon 2 (base pairs 205 to 276) and exon 3 (base pairs 277 to 556), respectively. The splice junctions comply with the ag-gt rule and are as follows: exon 2, 5'-tc ca cc ct agAC CTGAGCTCC...CCTCT CG AAAGgtaagacctc-3' and exon 3, 5'-ttttctgcag GTGGACAGCC-C... CTC CA GA AA AAgtaagacctt-3'. The genomic position of exons 1 and 4 to 16 were determined from P1-derived artificial chromosome clones RP11-796I2 (AC074257), RP5-1127D14 (AC006358), RP4-563H24 (AC006966). Analysis of genomic sequence data indicates the PRKAG2 gene is
280 kb in size located at 7q36 of chromosome 7.
Missense Mutation in the PRKAG2 Gene
A missense mutation, Arg531Gly, in exon 15 of PRKAG2 was identified and shown to be present in all living affected family members. The mutation results from guanine (G) substituted for cytosine (C) at nucleotide 1681 (GenBank accession number AJ249976). This base pair substitution creates a restriction enzyme recognition site for NIaIII. Restriction enzyme digestion with NIaIII of DNA from family members provided confirmation of the mutation, showing the expected novel digestion pattern only in the affected members. Direct DNA sequencing of 150 unrelated healthy white individuals did not show this mutation.
| Discussion |
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Determination of the intron-exon structure of the PRKAG2 gene showed that it consists of 16 exons and is
280 kb in size. Recently, it was determined that a smaller transcription product of PRKAG2 exists as a result of an alternative transcription initiation site in intron 4.6 Thus, this smaller transcript corresponds to exons 5 to 12 of the full-length transcription product. The full-length and truncated transcripts, denoted PRKAG2a and PRKAG2b, respectively, are highly expressed in cardiac tissue.6,7 The previously and currently described mutations are present in exons 7 and 15, and are therefore common to both PRKAG2 transcription products.
AMPK, a serine/threonine kinase, is known to have multiple cellular functions, which may account for the diverse phenotype of ventricular preexcitation, conduction system disease, and cardiac hypertrophy, as has been emphasized in recent studies.5,8 Evidence suggests that AMPK regulates gene transcription,9 and mutations in transcription factors are known to induce congenital heart malformations.10 The mutant AMPK presumably alters atrioventricular septation during cardiogenesis, leading to the presence of accessory atrioventricular fibers responsible for ventricular preexcitation. Atrial fibrillation may occur in
15% of sporadic WPW cases.11 The much higher incidence of atrial fibrillation and conduction defects observed in this syndrome suggests that AMPK, through phosphorylation, regulates cardiac ion channels.12 The identification of the cardiac ion channel(s) serving as substrate for AMPK not only would provide insight into the molecular basis of these common rhythm disturbances but also would suggest targets for the development of more specific therapy. This is particularly significant in consideration of the fact that the molecular mechanism for atrial fibrillation from any cause remains elusive. Interestingly, systemic hypertension was present, as was also observed in our previous large kindred. AMPK regulates endothelial nitric oxide synthase (eNOS), a key regulator of blood pressure homeostasis.13 The eNOS mouse knockout model exhibits a phenotype of hypertension and hypertrophy.14 Thus, impaired regulation of eNOS may induce hypertrophy and hypertension.
| Acknowledgments |
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| Footnotes |
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Received September 10, 2001; revision received November 5, 2001; accepted November 5, 2001.
| References |
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Wiedermann CJ, Becker AE, Hopferwieser T, et al. Sudden death in a young competitive athlete with Wolff-Parkinson-White syndrome. Eur Heart J. 1987; 8: 651655.
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Basso C, Corrado D, Rossi L, et al. Ventricular preexcitation in children and young adults: atrial myocarditis as a possible trigger of sudden death. Circulation. 2001; 103: 269275.
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Gollob MH, Green MS, Tang A, et al. Identification of a gene responsible for familial Wolff-Parkinson-White syndrome. N Engl J Med. 2001; 344: 18231864.
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Blair E, Redwood CS, Ashrafian H, et al. Mutations in the gamma(2) subunit of AMP-activated protein kinase cause hypertrophic cardiomyopathy: evidence for the central role of energy comp disease pathogenesis. Hum Mol Genet. 2001; 10: 12151220.
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Schott JJ, Benson DW, Basson CT, et al. Congenital heart disease caused by mutations in the transcription factor NKX2-5. Science. 1998; 281: 108111.
11. Bauernfeind RA, Wyndham CR, Swiryn SP, et al. Paroxysmal atrial fibrillation in the Wolff-Parkinson-White syndrome. Am J Cardiol. 1981; 47: 562569.[Medline] [Order article via Infotrieve]
12. Hallows KR, Raghuram V, Kemp BE, et al. Inhibition of cystic fibrosis transmembrane conductance regulator by novel interaction with the metabolic sensor AMP-activated protein kinase. J Clin Invest. 2000; 105: 17111721.[Medline] [Order article via Infotrieve]
13. Chen ZP, Mitchelhill KI, Michell BJ, et al. AMP-activated protein kinase phosphorylation of endothelial NO synthase. FEBS Lett. 1999; 443: 285289.[Medline] [Order article via Infotrieve]
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Shesely EG, Maeda N, Kim HS, et al. Elevated blood pressures in mice lacking endothelial nitric oxide synthase. Proc Natl Acad Sci U S A. 1996; 93: 1317613181.
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