Emerin deletion reveals a common X-chromosome inversion mediated by inverted repeats

Emery-Dreifuss muscular dystrophy (EMD) is an X-linked disorder characterized by contractures, progressive muscle weakness and cardiomyopathy(1-3). The emerin gene, located in human Xq28, is approximately 2 kb in length, is composed of 6 exons and falls within a 219-kb region that has been completely sequenced(4-6). Immediately centromeric to emerin is the 26-kb filamin gene (FLN1), composed of 48 exons and encoding the actin-binding protein 280 (refs 7,8). Flanking this 48-kb FLN1/emerin region are two large inverted repeats, each 11.3 kb, that exhibit >99% sequence identity(6). The high level of genomic detail in this region allowed us to characterize the first complete emerin gene deletion mutation that also involved a partial duplication of the nearby FLN1 gene, This rearrangement could be explained by mispairing of the large inverted repeats, followed by double recombination among one set of mispaired repeats and internal sequences. Furthermore, our characterization of this rare DNA rearrangement revealed a more common result of the mispairing of these large inverted repeats - recombination contained within the inverted repeats leading to the maintenance of repeat sequence homogeneity and inversion of the 48-kb FLN1/emerin region. The presence of this frequent inversion, found in the heterozygous state in 33% of females, helps to explain the discrepancies observed between the genetic and physical map distances in this region of the X chromosome. It also illustrates the biological insights which can be gleaned by sequencing the human genome.