This study is an observational study that aims to advance our knowledge on infantile onset FSHD. The study will include 50 participants of all ages who have presented with symptoms of FSHD between birth and 10 years of age. Study participation will involve a single day of assessments at one of the participating CINRG centers (to include physical exam, cognitive testing, eye exam, hearing test, strength testing and speech evaluations). The procedures may be split over additional days for scheduling purposes.

Inclusion Criteria:

Affected participants must have a clinical diagnosis of FSHD, including the presence of all of the following features based on review of medical records and/or direct examination:

• Onset of symptoms involving the facial or shoulder girdle muscles
• Autosomal dominant inheritance in familial cases
• Contraction of the D4Z4 repeat array from 1-10 (10 - 38 kb) copies in the 4q35 subtelomeric region, based on established molecular genetic techniques

Exclusion Criteria:

• Symptomatic cardiomyopathy or severe cardiac arrhythmia which may limit the ability to complete the study protocol
• Maternal/mitochondrial mode of inheritance
• Evidence of an alternative diagnosis based on muscle biopsy or other available investigations

Individuals with infantile onset (diagnosed at birth until 10 years of age) and genetically confirmed FSHD will be recruited. This will include children and youth (less than 18 years old) with FSHD who are currently followed in pediatric neuromuscular centers, as well as adults (18 years or older) with FSHD who are identified as having infantile onset of disease by chart review, clinical exam, and genetic confirmation.