RESUMEN
INTRODUCTION: Syncope and palpitations as the only initial manifestations of myotonic dystrophy type 1 (MD1) due to a CTG expansion of 50-100 repeats have not been reported. CASE REPORT: In a 55-year-old female with a family history of MD1 and a personal history of a single syncope, palpitations, and hyperCKemia, 70 CTG repeats were detected in the DMPK gene. Her brother had presented atypical clinical, electromyographic, and muscle biopsy features since the age of 35 but had been diagnosed with MD1 after he later developed typical distal myotonia. He died suddenly during an episode of syncope at the age of 53. A sister with clinical myotonia died suddenly during sleep at the age of 45 and a second sister with quadriparesis died from complications of intestinal rupture at age 52. A third sister committed suicide at age 40 after developing recurrent syncopes, while a fourth sister had hyperCKemia and foot-extensor weakness. The mother of these five affected children died suddenly from myocardial rupture. CONCLUSIONS: MD1 with <100 CTG repeats may exclusively manifest cardiologically. Family screening for MD1 is important even in asymptomatic patients. MD1 may initially manifest without typical features, while muscle biopsy may be misleading and indicate glycogenosis. Close cardiac follow-up is important if MD1 manifests cardiologically to prevent syncope or sudden cardiac death.