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 ECG, 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 enddiastolic 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.