Objective Pelizaeus-Merzbacher disease (PMD; OMIM 312080) is a rare X-linked recessive disorder presenting with nystagmus,impaired motor development,ataxia,and progressive spasticity.Traditionally,PMD is divided into classical,transitional and connatal types.The main cause of PMD is Proteolipid protein (PLP 1) gene abnormalities.PLP1 gene (GenBank NM_000533) is located at chromosome Xq22.2,covers approximately 17 kb genomic DNA and contains seven exons encoding 276 amino acids.Duplication of the PLP1 gene is the most frequent gene defect,accounting for 50%-70% of PMD cases,whereas point mutations in the coding sequence or affecting splice sites account for 10%-25% of PMD cases.Multiplex ligation-dependent probe amplification (MLPA) is based on the ligation of two adjacent annealing oligonucleotides followed by quantitative PCR amplification of the ligated products.MLPA has been described recently,which is a efficient method to detect DNA duplications and deletions.