Quantitative MRI measurements are considered the gold standard for assessing lean muscle volume and disease biomarkers (fat volumes vs. lean muscle volumes and STIR+ presence) that may be modulated by treatment. Muscle fat replacement and free-water hyperintensity indicate early disease changes before functional performance is affected. Muscles with low lean muscle volume and an intermediate fat fraction (10-55%) predict disease progression over 1-2 years.

Investigators will use whole-body MRI to measure lean muscle volume (mL) in pediatric subjects and compare these measurements with other factors to create a composite score over a two-year period.

Quantitative MRI measurements are considered the gold standard for assessing lean muscle volume and disease biomarkers (fat volumes, fat fraction and STIR+ presence) that may be modulated by treatment. The use of MRI has shown as a technique to predict disease progression.

Investigators will use whole-body MRI to measure total volume (mL) in pediatric subjects and compare these measurements with other factors to create a composite score over a two-year period. This refers to the overall volume of a specific tissue or organ measured in milliliters (mL) using MRI.

Quantitative MRI measurements are considered the gold standard for assessing lean muscle volume and disease biomarkers, such as the percentage of lean muscle volume with Short Tau Inversion Recovery (STIR) enhancement. STIR MRI helps predict disease progression by highlighting areas of inflammation and edema within muscle tissue. This provides valuable insights into underlying disease processes, aiding in the prediction of progression and guiding treatment decisions.

Investigators will use whole-body MRI to measure STIR positivity, indicating inflammation and edema, in pediatric subjects. These measurements will be compared with other factors to create a composite score over a two-year period.

assess the impact of fatigue on individuals with neurological conditions, measuring their severity, frequency, and effects on daily activities and quality of life using a 5- point rating system (1 being never and 5 being always).

is a 5-item questionnaire which assesses the physical impact of facial weakness. The responses (graded 1-5, 5 being no difficulty and 1 being unable to do) are summed to create a total score, which is then converted into a percentage scale. A score of 100% represents normal function, while lower scores indicate increasing levels of disability.

measures how well people with neuromuscular disorders can perform daily activities. It includes 22 questions about tasks such as dressing, bathing, and walking, with difficulty rated as impossible, difficult, or easy.

is a tool used to screen for emotional and behavioral problems in children and adolescents aged 2 to 17. It consists of 25 questions divided into five categories: emotional symptoms, conduct problems, hyperactivity/inattention, peer relationship problems, and prosocial behavior. Each item is rated on a 3-point scale (0= not true, 1 = somewhat true and 2 = certainly true)

Is a rating scale that patients can use to measure how severe they feel their symptoms are. Patients rate their condition on a scale from 1 (Normal) to 4 (Severe). This will serve as one of the study anchors.

is an instrument developed to assess quality of life and how disease has changed since last visit. the purpose of the "domain-delta" questionnaire is to determine each patient's perceived change in their health-related quality-of-life in the last 6-months. This questionnaire will inquire about total health as well as health related to 14 subdomains self-identified as important by patients during development of the FSHD Health Index. Participants indicate their perceived change by answering if an area "is a lot worse", "is a little worse", "there has been no change", "it is a little better", or "it is a lot better" for each subdomain. This will serve as one of the other anchors in the study.

a tool used by clinicians to evaluate motor abilities in individuals with dysferlinopathy, a type of muscular dystrophy. It measures how well patients can perform various physical tasks, helping to track the progression of the disease. This assessment is useful for both walking and non-walking patients, providing important information to guide treatment and care plans. This will be used in comparison to how well the FSHD-COM Peds assessing subjects

an assessment tool used to evaluate upper limb function in individuals with muscular dystrophies, such as Duchenne muscular dystrophy. It measures the ability to perform various motor tasks, providing insights into the strength and mobility of the arms and hands. The PUL helps track disease progression and guides treatment decisions by capturing detailed information about upper limb capabilities. This will be helpful in assessing Cohort two as well as will be utilized to the FSHD-COM Peds and RWS.

is a fixed-distance assessment used to measure an individual's maximum ambulatory ability. Participants are asked to walk or run 100 meters as quickly as they can, depending on their capability. This test is commonly used in research to evaluate physical performance and mobility, particularly in individuals with conditions affecting their walking ability. It helps researchers track changes in mobility over time and assess the effectiveness of interventions aimed at improving walking speed and endurance

assess the impact of pain on individuals with neurological conditions, measuring their severity, frequency, and effects on daily activities and quality of life using a 5- point rating system (1 being never and 5 being always).

Is a rating scale that patients can use to measure if any change in severity has occurred since being in the study. patient rate their change on a scale from 1 to 7 (1 being no change or worse and 7 being a great deal better or improvement that has made all the difference). This will serve as one of the study anchors.