Myotonic dystrophy type 1 (DM1) can affect people in many different ways, even in the same family. The symptoms that children experience can be different and more severe than adults. Prior studies in children have been limited because only a small number of children could participate. In this study, we hope to learn more about these differences and what causes them.

This is an observational study conducted in participants' homes and does not require travel. Instead, we will use video calls to talk with children and their parents/guardians about DM1 symptoms and how it affects the child's muscles, heart, and brain. We'll send families an iPad and the other tools they need for the study. During the video call, kids will do some simple activities to see how their body moves and functions. Parents/guardians might need to help their child with some of these activities.

After the video visit, we'll get a small blood sample from the child. This can be done at a local lab or even at home. We'll then look at the child's genes in the blood sample to understand how they might be linked to their symptoms. Parents/guardians can chose to have their child's genetic test result returned to them.

Inclusion Criteria:

• Age 0-17 years
• Clinical diagnosis of congenital, childhood, or juvenile DM1
• English speaking
• Parent or guardian willing to assist and provide consent for participation
• If appropriate based on age and developmental level, child willing to provide assent for their own participation
• Available wifi

Exclusion Criteria:

• Presence of any other non-DM1 illness or disease (e.g. other neuromuscular disorder, cerebral palsy, or other genetic or acquired disorder affecting the central or peripheral nervous system) that could interfere with study results in the opinion of the site investigator
• Significant recent trauma or injury prior to the RSV that could affect functional assessment

Myotonic dystrophy DM1 between the ages of 0-17 years old

Aggregated and deidentified data will be shared with qualified investigators.