tokens: The association between normal alleles at the CTG repeat and two nearby polymorphisms in the myotonin protein kinase gene , the Alu insertion / deletion polymorphism and the myotonic dystrophy kinase ( DMK ) ( G / T ) intron 9 / HinfI polymorphism , has been analyzed in South African Negroids , a population in which myotonic dystrophy ( DM ) has not been described .