|Number of repeats||Counts (alleles)||Percentage|
Overview of repeats
Myotonic dystrophy type 1 (DM1) is a progressive neuromuscular disease due to CTG trinucleotide expansions in the 3′ UTR of DMPK gene, which is caused by at least 50 repeats (Brook et al., 1992). Salehi et al. (2007) research demonstrated that disease severity is correlated with repeat length and more muscular disability is seen at longer repeats. Affected individuals with expansions up to 100 repeats usually develop mild symptoms or asymptomatic (Salehi et al., 2007). The most severe phenotype of this disease can be observed in individuals with long repeats, which can even reach up to thousands of repeats (Jaspert et al., 1995). In a healthy population, allele length ranges 5-34 CTG repeats, while premutation alleles are defined to be between 35 and 49 repeats (Gutiérrez Gutiérrez et al., 2020). These individual has no symptoms but whose offspring can acquire the allele and may reach to the pathogenic range (Gutiérrez Gutiérrez et al., 2020).