A severe connatal form of Pelizaeus Merzbacher disease in a Czech boy caused by a novel mutation (725C>A, Ala242Glu) at the 'jimpy(msd) codon' in the PLP gene.

Pelizaeus Merzbacher disease (PMD) is an X-linked recessive disorder of the central nervous system myelination caused by mutations involving the proteolipid protein gene (PLP). Early nystagmus and developmental delay, progressive pyramidal, cerebellar and dystonic signs as well as white matter changes in brain MRI are typical for PMD. The PLP gene can be affected by two major types of mutations. A duplication of the whole PLP gene is the most common mutation and results usually in the milder classical phenotype, whereas point mutations in PLP gene often result in the rarer and more severe connatal form of PMD. The PLP protein is a higly conserved across species and is identical in human, mouse and rat. We describe a 13-year-old Czech boy with an early and severe developmental delay. His maternal uncle died at the age of one year and was also early and severely psychomotoricly retarded. The patient was the first child of healthy unrelated parents born after an uneventful pregnancy and delivery in 1988. Hyperbilirubinemia and bronchopneumonia and early stridor complicated his neonatal period. Diffuse hypotonia, nystagmus, psychomotor retardation, visual and hearing impairment have been observed in the patient since the age of 6 weeks. White matter abnormalities, cortical and periventricular atrophy were detected by MRI at the age of 6 and 11 years, respectively. Despite these signs and results an accurate clinical diagnosis was unclear until the age of 11 years. Last neurological examination in 1999 showed no nystagmus anymore, but extremely dystrophic limbs, truncal deformation, due to severe scoliosis, tetraplegia with hyperreflexia in C5C7 and areflexia L2S2 and positive pyramidal signs. The boy had no visual or speech contact. DNA tests followed the clinical suspicion for PMD. At first, duplication of PLP gene was excluded by quantitative comparative PCR. Direct sequencing of PLP gene detected a novel mutation in exon 6, a missense mutation 725C-->A (Ala242Glu) in the patient and in his mother and later also in his maternal grandmother. The same codon, but to valine (Ala242Val) is mutated in jimpy(msd) mouse, which is the frequently used animal model for PMD. Prenatal diagnosis for the next pregnancy has been offered to the family. The patient died recently at the age of 13 years due to respiratory failure. Our results support the data on the importance of this conserved amino acid alanine at codon 242.

Nijmegen breakage syndrome in 13% of age-matched Czech children with primary microcephaly.

The Nijmegen breakage syndrome is a rare autosomal recessive chromosomal instability disorder characterized by early growth retardation, congenital microcephaly, immunodeficiency, borderline mental development, and a high tendency to lymphoreticular malignancies. Most Nijmegen breakage syndrome patients are of Slavonic origin, and all of them known so far carry a founder homozygous 5 nucleotide deletion in the NBS1 gene. Microcephaly was present in 100% of Nijmegen breakage syndrome patients in a recent large international cooperative study. The frequency of Nijmegen breakage syndrome among children with primary microcephaly was not known. Early correct diagnosis of the syndrome is crucial for appropriate preventive care and therapy. We tested 67 Czech patients of different ages with simple microcephaly for the presence of the most common mutation in the NBS1 gene. Three new Nijmegen breakage syndrome cases were detected in this cohort, representing 4.5% of the cohort. All these newly diagnosed Nijmegen breakage syndrome patients were younger than 10 months at the time of diagnosis. They were all born within a 2.5-year period. Twenty-three of the 67 children in the cohort were born within this 2.5-year period, representing a 13% incidence of Nijmegen breakage syndrome. Frequency of Nijmegen breakage syndrome heterozygotes among infants in the Czech Republic is 1: 130-158 and the birth rate is 90,000 per year, therefore in the time span of 2.5 years, three new Nijmegen breakage syndrome homozygotes are expected to be born. Therefore we assume that by DNA testing of Czech primary microcephalic children it is possible to detect all Nijmegen breakage syndrome patients to be expected. The age at correct diagnosis was lowered from 7.1 years at the time before DNA testing, to well under 1 year of age. All new Nijmegen breakage syndrome patients could receive appropriate preventive care, which should significantly improve their life expectancy and prognosis.

Three new PLP1 splicing mutations demonstrate pathogenic and phenotypic diversity of Pelizaeus-Merzbacher disease.

Pelizaeus-Merzbacher disease is a severe X-linked disorder of central myelination caused by mutations affecting the proteolipid protein gene. We describe 3 new PLP1 splicing mutations, their effect on splicing and associated phenotypes. Mutation c.453_453+6del7insA affects the exon 3B donor splice site and disrupts the PLP1-transcript without affecting the DM20, was found in a patient with severe Pelizaeus-Merzbacher disease and in his female cousin with early-onset spastic paraparesis. Mutation c.191+1G>A causes exon 2 skipping with a frame shift, is expected to result in a functionally null allele, and was found in a patient with mild Pelizaeus-Merzbacher disease and in his aunt with late-onset spastic paraparesis. Mutation c.696+1G>A utilizes a cryptic splice site in exon 5, causes partial exon 5 skipping and in-frame deletion, and was found in an isolated patient with a severe classical Pelizaeus-Merzbacher. PLP1 splice-site mutations express a variety of disease phenotypes mediated by different molecular pathogenic mechanisms.