The spectrum of PLP1 gene mutations in patients with the classical form of the Pelizaeus-Merzbacher disease.

The Pelizaeus-Merzbacher disease (PMD) is a rare X-linked recessive hypomyelination disorder caused by mutations of the proteolipid protein1 gene (PLP1). There is a spectrum of PLP1-related disorders from very severe connatal PMD, through classical PMD to mild spastic paraplegia type 2 (SPG2), with some correlation between the type of mutation and the phenotype. In general, missense mutations give rise to more severe forms of the disease, deletions and null mutations to mild PMD and SPG2. The most common variations, duplications, result in the classical-intermediate form of PMD. To report the analysis of mutations in the PLP1 gene and phenotype di!erences in ten male patients diagnosed with PMD. Although they had different types of PLP1 mutations (duplications, missense and nonsense mutations), all of them were clinically classi"ed with the classical form of PMD (clPMD). The subjects of analysis were ten male patients aged 1.5 to 21 years who were diagnosed with PMD. All patients developed the "rst clinical symptoms between 1 an 8 months of age and showed developmental delay, mainly in motor skills. All were classified with the classical form of the disease, according to international clinical criteria and the electrophysiological and brain MRI criteria of hypomyelination. The molecular analysis of the PLP1 gene involved dosage analysis and direct sequencing of all exons and promotor region of the gene. The clinical diagnosis of PMD was con"rmed for all subjects by molecular analysis of the PLP1gene. Although all had the classical form of PMD, it was caused by mutations of di!erent types: duplications of the entire gene, missense and nonsense mutations. Our clinical and molecular "ndings showed that the phenotypic spectrum resulting from PLP1 mutations seems to be broader in patients with the PLP1 gene duplication compared to patients with both nonsense and missense mutation. Nevertheless, apart from the type of mutation, all our patients’ clinical manifestation falls into the category of the classical form of PMD according to international criteria. Obviously the type of mutations, but also other unidentified factors may a!ect the clinical course of PMD.The Pelizaeus-Merzbacher disease (PMD) is a rare X-linked recessive hypomyelination disorder caused by mutations of the proteolipid protein 1 gene (PLP1). There is a spectrum of PLP1-related disorders from very severe connatal PMD, through classical PMD to mild spastic paraplegia type 2 (SPG2), with some correlation between the type of mutation and the phenotype. In general, missense mutations give rise to more severe forms of the disease, deletions and null mutations to mild PMD and SPG2. The most common variations, duplications, result in the classical-intermediate form of PMD. To report the analysis of mutations in the PLP1 gene and phenotype differences in ten male patients diagnosed with PMD. Although they had di!erent types of PLP1 mutations (duplications, missense and nonsense mutations), all of them were clinically classi"ed with the classical form of PMD (clPMD). The subjects of analysis were ten male patients aged 1.5 to 21 years who were diagnosed with PMD. All patients developed the "rst clinical symptoms between 1 an 8 months of age and showed developmental delay, mainly in motor skills. All were classified with the classical form of the disease, according to international clinical criteria and the electrophysiological and brain MRI criteria of hypomyelination. The molecular analysis of the PLP1 gene involved dosage analysis and direct sequencing of all exons and promotor region of the gene. The clinical diagnosis of PMD was con"rmed for all subjects by molecular analysis of the PLP1 gene. Although all had the classical form of PMD, it was caused by mutations of di!erent types: duplications of the entire gene, missense and nonsense mutations. Our clinical and molecular findings showed that the phenotypic spectrum resulting from PLP1 mutations seems to be broader in patients with the PLP1 gene duplication compared to patients with both nonsense and missense mutation. Nevertheless, apart from the type of mutation, all our patients' clinical manifestation falls into the category of the classical form of PMD according to international criteria. Obviously the type of mutations, but also other unidentified factors may a!ect the clinical course of PMD.