RESUMO
We investigated sequence alternation, promoter methylation, and loss of heterozygosity (LOH) of the RB1 gene as possible mechanisms of its inactivation in retinoblastoma. In 42 Chinese patients with sporadic retinoblastoma, the promoter and entire coding region of RB1 were examined for sequence changes. Status of methylation of the CpG-rich island at the 5'end was determined by methylation specific PCR assay. We detected 15 RB1 mutations in 38% (16/42) of the retinoblastoma patients, among them 19% (8/42) were germ-line mutations. A total of nine novel mutations were identified: E54X, S114X, I126S, g73779insG, D718N, IVS2+1G>C, IVS14+1G>C, IVS21+1G>C, and a complex alteration g78177G>T/g78176insTT leading to 543X. Most of them are likely to affect the RB1large pocket domain through the production of truncated gene products. None of the DNA samples showed methylation at the RB1promoter. In 15 cases where both normal and cancerous retinoblastoma tissue specimens were available, allelic loss according to microsatellite markers within or distal to the RB1 locus was analyzed and immunohistological staining for RB1 expression performed. Among them, frequency of LOH at 13q14 was found to be high at 60% (9/15) with no segregation with unilateral tumors. All these nine tumors did not express RB1 protein, showing an association of LOH at the RB1 locus with its loss of expression in retinoblastoma. Our results indicate that the RB1 gene in sporadic retinoblastoma is commonly inactivated because of loss-of-function mutations and loss of heterozygosity but not by the epigenetic phenomenon of promoter hypermethylation.
Assuntos
Inativação Gênica , Genes do Retinoblastoma , Perda de Heterozigosidade , Mutação , Neoplasias da Retina/genética , Retinoblastoma/genética , Pré-Escolar , China , Cromossomos Humanos Par 13 , Ilhas de CpG , Metilação de DNA , Análise Mutacional de DNA , Feminino , Humanos , Imuno-Histoquímica , Lactente , Masculino , Pessoa de Meia-Idade , Regiões Promotoras Genéticas , Neoplasias da Retina/diagnóstico , Neoplasias da Retina/metabolismo , Retinoblastoma/diagnóstico , Retinoblastoma/metabolismo , Proteína do Retinoblastoma/genética , Proteína do Retinoblastoma/imunologia , Proteína do Retinoblastoma/metabolismo , Células Tumorais CultivadasRESUMO
A 63-year-old previously healthy woman developed a severe systemic infection 5 days after returning from a holiday to Southern Portugal. She subsequently died, and polymerase chain reaction of a blood sample was positive for Rickettsia conorii ssp israeliensis. The prevalence of severe forms of this illness in the Mediterranean Basin is discussed.