Fig. 7

Myotonic dystrophy clinical and molecular diagnostic diagram (Catalli et al. 2010; Udd and Krahe 2012; Wenninger et al. 2018; Gutiérrez Gutiérrez et al. 2020; Hamel 2022). Muscle biopsy is not necessary for diagnostic confirmation of Steinert´s myotonic dystrophy type 1 and molecular exams may be ordered in the first clinical examination if the characteristic clinical features are detected. The diagnosis of myotonic dystrophy type 2 requires a high level of clinical suspicion to guide the correct molecular confirmatory tests. CCTG expansion: cytosine-cytosine-thymine-guanine tetranucleotide repeat expansion; CLCN1 gene: chloride voltage-gated channel 1 gene; CNBP gene: CCHC-type zinc finger nucleic acid binding protein gene; CTG expansion: cytosine-thymine-guanine trinucleotide repeat expansion; DMPK gene: dystrophia myotonica protein kinase gene; yo: years old; ZNF9 gene (now CNBP gene): zinc finger protein 9 gene