Expression of human-specific lamin A/C and spectrin (Box 1) in tissue sections demonstrated that the engrafted myogenic cell lines carrying contracted alleles retain their ability to incorporate into regenerating muscle fibers, and reverse transcription polymerase chain reaction (RT-PCR) analysis confirmed contraction-specific expression of a DUX4-target gene, thereby showing that myogenic cell xenografts can provide an in vivo model for FSHD. This evidence concerns the gene DUX4 and facioscapulohumeral muscular dystrophy.