ANALYSIS OF THE CTG REPEAT IN SKELETAL-MUSCLE OF YOUNG AND ADULT MYOTONIC-DYSTROPHY PATIENTS - WHEN DOES THE EXPANSION OCCUR

The purpose of this investigation was to analyze the CTG expansion in muscle as compared to lymphocytes DNA in a sample of selected myotonic dystrophy (DM) patients of different ages and degrees of clinical sev erity, ranging from severe congenital to minimally affected. Results f rom the present study showed that the size of the CTG repeat was marke dly larger in skeletal muscle than in lymphocytes in all DM patients. In contrast to lymphocytes, no significant correlation was found betwe en the size of the CTG expansion in muscle and age at onset. In additi on, large expansions were observed in muscle from all adult symptomati c patients independently of the presence of muscle weakness, which rai ses the question of the value of analyzing CTG expansions in muscle fo r predicting the severity of the phenotype. Differences between the si ze of the CTG expansions in muscle as compared to lymphocytes were sma ller in affected children suggesting an apparent tendency to increase with aging and reaching a plateau in adulthood.