Coats syndrome is a rare extramuscular complication of facioscapulohumeral muscular dystrophy type 1 (FSHD1) associated with large D4Z4 contractions. This study was carried out to investigate the frequency of Coats syndrome and its association with D4Z4 contraction size in patients with FSHD1. The authors searched a North American FSHD registry and the University of Rochester (UR) FSHD research database, reviewed the literature, and sent surveys to 14 FSHD referral centers in the United States and overseas to identify patients with genetically confirmed FSHD1 with a diagnosis of Coats syndrome. Out of 357 genetically confirmed patients in a North American FSHD registry and 51 patients in the UR database, 3 patients had a self-reported history of Coats disease (0.8%; 95% confidence interval 0.2%-2.2%). In total, 14 patients with FSHD with known genetic contraction size and Coats syndrome, confirmed by ophthalmologic examination were identified: 10 from the authors’ survey and 4 from the literature. The median age at diagnosis of Coats syndrome was 10 years (interquartile range 14 years). The median D4Z4 fragment size was 13 kilobases (kb) (interquartile range 1 kb). One patient was mosaic (55% 11 kb, and 45% 78 kb). Closer surveillance for retinal complications is warranted in patients with D4Z4 fragments ≤15 kb.
