MYOTONIC DYSTROPHY TYPE 1

MYOTONIC DYSTROPHY IS AN AUTOSOMAL DOMINANT DISORDER CHARACTERIZED MAINLY BY MUSCULAR DYSTROPHY, CATARACTS, HYPOGONADISM, FRONTAL BALDING, AND ECG CHANGES. MYOTONIC DYSTROPHY TYPE 1 (DM1), HAS A SEVERE CONGENITAL FORM AND A MILDER CHILDHOOD-ONSET FORM AS WELL AS AN ADULT-ONSET FORM. THE GENETIC DEFECT IN DM1 RESULTS FROM AN AMPLIFIED TRINUCLEOTIDE REPEAT IN THE 3-PRIME UNTRANSLATED REGION OF DMPK GENE. DISEASE SEVERITY VARIES WITH THE NUMBER OF REPEATS: NORMAL INDIVIDUALS HAVE 5 TO 37 REPEATS, MILDLY AFFECTED PERSONS HAVE 50 TO 150 REPEATS, PATIENTS WITH CLASSIC DM HAVE 100 TO 1000 REPEATS, AND THOSE WITH CONGENITAL ONSET CAN HAVE MORE THAN 2000 REPEATS.