Myotonic Dystrophy Type 1 (DM1) is a genetic-based disorder transmitted in an autosomal dominant manner causing the expanded and unstable CTG repeat. DM1 is a multisystemic disease and, to varying degrees, CNS involvement has been described, including cognitive and brain structural alteration. However, the exact pattern of cognitive dysfunction and brain structural involvement is still to be established. Besides, an aging hypothesis has been suggested, but few attempts have been made in order to determine whether the observed alterations are neurodevelopmental or neurodegenerative. The present thesis aims to address the previously mentioned gaps in the literature through four scientific reports. Results highlight the existence of a domain-specific cognitive decline affecting primarily visuoconstructive abilities in early adulthood. Additionally, both global and regional brain atrophy is confirmed, with both clinical and neuropsychological markers of severity. Finally, the profile of natural brain history in DM1 reveals a neurodevelopmental process, as well as a potential neurodegeneration to which neuropsychological testing shows sensitivity.