The shortening of telomeres-the ends of chromosomes-affects a gene involved in a muscle disorder called facioscapulohumeral muscular dystrophy (FSHD).These results, reported this week in Nature Structural & Molecular Biology, describe the first known case in which increased expression of a gene near a shortening telomere contributes to human disease.

Telomeres shorten with age and, once they reach a critical length, can induce growth arrest and inhibit tumor growth. Telomere shortening can also affect the expression of genes near chromosome ends, a phenomenon called telomere position effect (TPE).

Woodring Wright and colleagues compared the effect of telomere length on the expression of the FSHD-associated DUX4 gene in cells derived from FSHD patients and their unaffected family members. The authors found that DUX4 expression is dramatically increased in FSHD-derived cells with short telomeres. The effect increases with decreasing telomere length and occurs long before growth arrest would be induced, suggesting that TPE could explain the delayed onset and progression of this prevalent muscle disorder. The authors also found it could affect genes at least 100 kb from the telomere, a distance much greater than anticipated.