Relation of cardiac abnormalities and CTG-repeat size in myotonic dystrophy

It is unclear if the severity of cardiac involvement in patients with myotonic dystrophy (MD) is related to the size of the CTG-repeat expansion. This open, uncontrolled. observational, prospective study aimed to find out if there is a relation between the severity of cardiac involvement in MD and the CTG-repeat size. In 21 patients with MD, (8 women, 13 men, aged 11-88 years) a detailed cardiologic examination, including history, clinical examination, electrocardiography (ECG), transthoracic echocardiography and ambulatory 24-h EGG, was carried out and cardiac involvement was assessed according to a previously described scoring system. Additionally, the CTG-repeat size was determined from nuclear DNA of blood leukocytes. The correlation between the CTG-repeat size and the mean heart rate, PQ-interval, QTc-interval, fractional shortening, left ventricular end-diastolic diameter, septal thickness, posterior wall thickness, mean heart rate on 24-h ECG and cardiac involvement score was r = 0.47, r = 0.086, r = 0.11, r = - 0.27, r = - 0.34, r = - 0.06, r = - 0.12, r = 0.16 and r = 0.09 (all p > 0.05), respectively. In patients 21-30, 31-40 and 41-50 years of age, cardiac involvement increased with increasing CTG-repeat size. In younger patients, the number of CTG-repeats needed to develop a reasonable cardiac involvement was higher than in older patients. Depending on age, cardiac involvement increases with increasing CTG-repeat size obtained from blood leukocytes in patients with MD.