Repeats Associated with Facioscapulohumeral Dystrophy (FSHD)
by: Weihua Zeng, Jessica C. de Greef, Yen-Yun Chen, Richard Chien, Xiangduo Kong, Heather C. Gregson, Sara T. Winokur, April Pyle, Keith D. Robertson, John A. Schmiesing, Virginia E. Kimonis, Judit Balog, Rune R. Frants, Alexander R. Ball, Leslie F. Lock, Peter J. Donovan, Silvère M. van der Maarel, Kyoko Yokomori
Author Summary: Most cases of facioscapulohumeral muscular dystrophy (FSHD) are associated with a decrease in the number of D4Z4 repeat sequences on chromosome 4q. How this leads to the disease remains unclear. Furthermore, D4Z4 shortening is not seen in a small number of FSHD cases, and the etiology is unknown. In the cell, the DNA, which encodes genetic information, is wrapped around abundant nuclear proteins called histones to form a "beads on a string"–like structure termed chromatin. It became apparent that these histones are modified to regulate both maintenance and expression of genetic information. In the current study, we characterized the chromatin structure of the D4Z4 region in normal and FSHD patient cells. We discovered that one particular histone modification (trimethylation of histone H3 at lysine 9) in the D4Z4 repeat region is specifically lost in FSHD. We identified the enzyme responsible for this modification and the specific factors whose binding to D4Z4 is dependent on this modification. Importantly, these chromatin changes were observed in both types of FSHD, but not in other muscular dystrophies. Thus, this chromatin abnormality at D4Z4 unifies the two types of FSHD, which not only serves as a novel diagnostic marker, but also provides new insight into the role of chromatin in FSHD pathogenesis.