RÉSUMÉ
<p><b>OBJECTIVE</b>Three long QT syndrome(LQTS) pedigrees were brought together for genetic diagnosis by using short tandem repeat(STR) markers.</p><p><b>METHODS</b>Genomic DNA was extracted from blood samples. STR markers (D7S1824, D7S2439, D7S483, D3S1298, D3S1767, D3S3521) in or spanning the HERG and SCN5A gene were amplified; the haplotype analysis for LQTS was performed.</p><p><b>RESULTS</b>Clinical diagnosis showed that 15 are LQTS patients (3 died) and 11 are probable patients. Linkage analysis showed that LQTS patients are linked with the SCN5A gene in family 1, HERG is linked with the disease in family 2 and 3. Fourteen gene carriers were identified, 2 patients and 7 probable patients were excluded.</p><p><b>CONCLUSION</b>Linkage analysis using STR markers can serve as useful tool for presymptomatic diagnosis.</p>