RESUMO
Transmissible spongiform encephalopathies (TSEs) are a group of rare fatal neurodegenerative disorders. Creutzfeldt-Jakob disease (CJD) represents the most common form of TSE and can be classified into sporadic, genetic, iatrogenic and variant forms. Genetic cases are related to prion protein gene mutations but they only account for 10-20% of cases. Here we report an apparently sporadic CJD case with negative family history carrying a mutation at codon 178 of prion protein gene. This mutation is a de novo mutation as the parents of the case do not show it. Furthermore the presence of three different alleles (wild type 129M-178D and 129V-178D and mutated 129V-178N), confirmed by different methods, indicates that this de novo mutation is a post-zygotic mutation that produces somatic mosaicism. The proportion of mutated cells in peripheral blood cells and in brain tissue was similar and was estimated at approximately 97%, suggesting that the mutation occurred at an early stage of embryogenesis. Neuropathological examination disclosed spongiform change mainly involving the caudate and putamen, and the cerebral cortex, together with proteinase K-resistant PrP globular deposits in the cerebrum and cerebellum. PrP typing was characterized by a lower band of 21 kDa. This is the first case of mosaicism described in prion diseases and illustrates a potential etiology for apparently sporadic neurodegenerative diseases. In light of this case, genetic counseling for inherited and sporadic forms of transmissible encephalopathies should take into account this possibility for genetic screening procedures.
Assuntos
Síndrome de Creutzfeldt-Jakob/genética , Mosaicismo , Mutação de Sentido Incorreto , Príons/genética , Alelos , Química Encefálica , Desenvolvimento Embrionário/genética , Encefalopatia Espongiforme Bovina/genética , Testes Genéticos/métodos , Humanos , Masculino , Pessoa de Meia-Idade , Proteínas Priônicas , Príons/análiseRESUMO
BACKGROUND: Between January 1993 and December 2003, 19 patients with familial prion diseases due to the D178N mutation were referred to the regional epidemiological registry for spongiform encephalopathies in the Basque Country in Spain, a small community of some 2,100,000 inhabitants. METHODS: Ten further patients belonging to the same pedigrees were retrospectively ascertained through neurological or neuropathological records. In four of the patients, the diagnosis was confirmed by analysing DNA obtained from paraffin blocks. In this article, we report on the clinical, genetic, and pathological features of the 23 patients carrying the D178N mutation confirmed by genetic molecular analysis. Haplotyping studies suggest a founder effect among Basque born families, explaining in part this unusually high incidence of the D178N mutation in a small community. Only two patients (8%) lack familial antecedents. RESULTS: We have observed a phenotypic variability even among homozygous 129MM patients. Our findings challenge the currently accepted belief that MM homozygosity in codon 129 is always related to a fatal familial insomnia (FFI) phenotype. Indeed, seven out of 17 patients with a 129MM genotype in this series presented with a Creutzfeldt-Jakob disease (CJD) clinicopathological picture. CONCLUSIONS: The considerable clinical and pathological overlapping observed among homozygous 129MM patients favours the view that FFI and CJD178 are the extremes of a spectrum rather than two discrete and separate entities. Other genetic or environmental factors apart from the polymorphism in codon 129 may play a role in determining the phenotypic expression of the D178N mutation in the PRNP gene.
Assuntos
Amiloide/genética , Síndrome de Creutzfeldt-Jakob/genética , Variação Genética/genética , Fenótipo , Mutação Puntual/genética , Adulto , Idade de Início , Idoso , Códon , Síndrome de Creutzfeldt-Jakob/etnologia , Análise Mutacional de DNA , Feminino , Efeito Fundador , Haplótipos , Humanos , Incidência , Masculino , Pessoa de Meia-Idade , Proteínas PrPSc/genética , Estudos Prospectivos , Distúrbios do Início e da Manutenção do Sono/epidemiologia , EspanhaRESUMO
BACKGROUND: Frontotemporal dementia with parkinsonism is often linked to chromosome 17 and is related to mutations in the MAPT gene. In some families the genetic basis is still unknown. The authors report two pedigrees with FTDP-17 harboring a novel mutation (K317M) in exon 11 in the MAPT gene. METHODS: The authors identified two apparently unrelated pedigrees with an autosomal dominant neurodegenerative condition. Thirteen patients were examined and eight autopsies were performed. RESULTS: Mean age at onset was 48 years. Mean disease duration was 6 years. Dysarthria often heralded the disease. All cases had parkinsonism and pyramidalism and half of them had amyotrophy. Behavioral or personality changes were not a prominent feature. Cognitive decline appeared late in the evolution. Neuropathologically, a massive degeneration of the substantia nigra without Lewy bodies was a constant finding. A variable degree of frontotemporal atrophy was found. Corticospinal tract degeneration and anterior horn neuron loss were present in six of seven autopsies in which the spinal cord was examined. An extensive deposition of abnormal tau protein in a mixed pattern (neuronal, glial) was observed. Pick's bodies were not seen. Biochemical analysis of tau revealed two bands of 64 and 68 kDa. CONCLUSION: Genetic analysis revealed the same novel mutation (K317M) in exon 11 of the MAPT gene in both pedigrees. A common haplotype between members of the two pedigrees suggests that they belong to the same family.
