Epigenetic dysregulation of the D4Z4 locus in humans causes a muscular dystrophy called FSHD (FacioScapuloHumeral muscular Dystrophy). D4Z4 is one of the most challenging genomic regions to study, as a tandem array of large (3-kb) repeats. To resolve allele-specific genetic structure and DNA methylation, we use long-read nanopore sequencing. Combining whole-genome ultra-long sequencing with targeted (Cas9-mediated) sequencing of D4Z4 improves diagnosis of FSHD and sheds light on the role of epigenetic regulator SMCHD1 at this locus.