This study will investigate two promising outcome measures that can be used in children diagnosed with FSHD. The Facioscapulohumeral Dystrophy-Composite Outcome Measure (FSH-COM) and Facioscapulohumeral Dystrophy Health Index (FSH-HI) are two FSHD-specific outcomes that have been used in adults with the condition, however their usefulness in children with the condition are less well known. The FSH-COM evaluates physical function (what the person can do), while the FSH-HI measures a person’s perception of disease burden (the impact the condition has on their life). This study will specifically look at the reliability and validity of these two outcomes measures in children aged 5-18 years with a genetic diagnosis of FSHD. As well as looking at how consistent these outcome measures are over a short time period, we will also compare these FSHD specific measures with two other measures of physical functioning and quality of life, the Motor Function Measure (MFM), and the Paediatric Quality of Life (PedsQL™) neuromuscular module. A better understanding of the reliability and validity of these measures in children with FSHD will enhance their readiness for use in future clinical studies, improving our ability to rapidly and effectively assess the efficacy (or lack thereof) of therapeutic agents for FSHD in children.