Genome rearrangements are a hallmark of human genomic disorders and occur largely through recombination mechanisms. In this issue, Lee et al. (2007) show that the complex nonrecurrent rearrangements observed in the dysmyelinating disorder Pelizaeus-Merzbacher disease (PMD) are likely to be caused by a replication mechanism involving template switching.

Chromosome Xq22.2 contains the entire proteolipid protein 1 gene (PLP1), and a genomic duplication in that chromosome is responsible for Pelizaeus-Merzbacher disease (PMD). Duplication can be detected using several molecular diagnostic methods such as comparative multiplex PCR, fluorescent in situ hybridization (FISH), restriction site polymorphism (RSP) analysis, and multiplex ligation-dependa...