PROGRESSIVE EXPANSION OF THE MYOTONIC-DYSTROPHY CTG REPEAT IN ASYMPTOMATIC INDIVIDUALS IN 3 SUCCESSIVE GENERATIONS OF A FAMILY

We report a family in which expansion of CTG repeats was detected in a symptomatic carriers of the myotonic dystrophy allele in three success ive generations. PCR-based analysis of the expanded CTG repeat reveale d intergenerational amplification of the mutation. We show here that t he myotonic dystrophy mutation may remain clinically silent, not only in the oldest generation of a family, but even among siblings and offs pring of symptomatic cases. This may represent a mechanism for the mai ntenance of the myotonic dystrophy gene in the population.