Genetic Testing in the Long QT Syndrome

Development and Validation of an Efficient Approach to Genotyping in Clinical Practice

Napolitano, Carlo MD, PhD
Priori, Silvia G. MD, PhD
Schwartz, Peter J. MD
Bloise, Raffaella MD
Ronchetti, Elena PhD
Nastoli, Janni BS
Bottelli, Georgia BS
Cerrone, Marina MD
Leonardi, Sergio MD

Molecular Cardiology, IRCCS Fondazione S. Maugeri Foundation (Drs Napolitano, Priori, Bloise, Ronchetti, Cerrone, and Leonardi and Mss Nastoli and Bottelli); Department of Cardiology, University of Pavia (Drs Priori and Schwartz); and IRCCS Policlinico S. Matteo (Dr Schwartz), Pavia, Italy.

Corresponding Author: Silvia G. Priori, MD, PhD, Molecular Cardiology, Maugeri Foundation, University of Pavia, Via Ferrata 8, 27100 Pavia, Italy ([email protected]).

Author Contributions: Drs Napolitano and Priori had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

Study concept and design: Napolitano, Priori.

Acquisition of data: Napolitano, Bloise, Ronchetti, Nastoli, Bottelli, Cerrone, Leonardi.

Analysis and interpretation of data: Napolitano, Priori, Schwartz, Ronchetti, Nastoli, Bottelli, Leonardi.

Drafting of the manuscript: Napolitano, Priori, Ronchetti, Nastoli, Bottelli, Cerrone, Leonardi.

Critical revision of the manuscript for important intellectual content: Napolitano, Priori, Schwartz, Bloise, Cerrone.

Statistical analysis: Napolitano, Priori, Bloise, Ronchetti, Nastoli, Bottelli, Leonardi.

Obtained funding: Priori.

Administrative, technical, or material support: Priori, Schwartz.

Study supervision: Priori, Bloise.

Financial Disclosures: Dr Priori has a patent pending for the proposed screening algorithm. Otherwise, none were reported.

Funding/Support: This work was supported by grants GP0227Y01 and GGP04066 Telethon, 2003/180 Ricerca Finalizzata, RBNE01XMP4_006 and RBLA035A4X_002FIRB, 2001067817_003 COFIN, HL68880 National Institutes of Health.

Role of the Sponsors: The funding organizations did not participate in the design and conduct of the study, and in the collection, analysis, and interpretation of the data, or in the preparation, review, or approval of the manuscript.

Additional Information: The eTable of novel mutations is available http://jama.com.

JAMA: The Journal of the American Medical Association 294(23):p E1-E3, December 21, 2005.

Context

In long QT syndrome (LQTS), disease severity and response to therapy vary according to the genetic loci. There exists a critical need to devise strategies to expedite genetic analysis.

Objective

To perform genetic screening in patients with LQTS to determine the yield of genetic testing, as well as the type and the prevalence of mutations.

Design, Patients, and Setting

We investigated whether the detection of a set of frequently mutated codons in the KCNQ1, KCNH2, and SCN5A genes may translate in a novel strategy for rapid efficient genetic testing of 430 consecutive patients referred to our center between June 1996 and June 2004. The entire coding regions of KCNQ1, KCNH2, SCN5A, KCNE1, and KCNE2 were screened by denaturing high-performance liquid chromatography and DNA sequencing. The frequency and the type of mutations were defined to identify a set of recurring mutations. A separate cohort of 75 consecutive probands was used as a validation group to quantify prospectively the prevalence of the recurring mutations identified in the primary LQTS population.

Main Outcome Measures

Development of a novel approach to LQTS genotyping.

Results

We identified 235 different mutations, 138 of which were novel, in 310 (72%) of 430 probands (49% KCNQ1, 39% KCNH2, 10% SCN5A, 1.7% KCNE1, and 0.7% KCNE2). Fifty-eight percent of probands carried nonprivate mutations in 64 codons of KCNQ1, KCNH2, and SCN5A genes. A similar occurrence of mutations at these codons (52%) was confirmed in the prospective cohort of 75 probands and in previously published LQTS cohorts.

Conclusions

We have developed an approach to improve the efficiency of genetic screening for LQTS. This novel method may facilitate wider access to genotyping resulting in better risk stratification and treatment of LQTS patients.