RESUMO
Choroideremia (CHM) is an x-linked recessive chorioretinal dystrophy, with 30% caused by nonsense mutations in the CHM gene resulting in an in-frame premature termination codon (PTC). Nonsense-mediated mRNA decay (NMD) is the cell's natural surveillance mechanism that detects and destroys PTC-containing transcripts, with UPF1 being the central NMD modulator. NMD efficiency can be variable amongst individuals with some transcripts escaping destruction, leading to the production of a truncated non-functional or partially functional protein. Nonsense suppression drugs, such as ataluren, target these transcripts and read-through the PTC, leading to the production of a full length functional protein. Patients with higher transcript levels are considered to respond better to these drugs, as more substrate is available for read-through. Using Quantitative reverse transcription PCR (RT-qPCR), we show that CHM mRNA expression in blood from nonsense mutation CHM patients is 2.8-fold lower than controls, and varies widely amongst patients, with 40% variation between those carrying the same UGA mutation [c.715 C>T; p.(R239*)]. These results indicate that although NMD machinery is at work, efficiency is highly variable and not wholly dependent on mutation position. No significant difference in CHM mRNA levels was seen between two patients' fibroblasts and their induced pluripotent stem cell-derived retinal pigment epithelium. There was no correlation between CHM mRNA expression and genotype, phenotype or UPF1 transcript levels. NMD inhibition with caffeine was shown to restore CHM mRNA transcripts to near wild-type levels. Baseline mRNA levels may provide a prognostic indicator for response to nonsense suppression therapy, and caffeine may be a useful adjunct to enhance treatment efficacy where indicated.
Assuntos
Coroideremia/tratamento farmacológico , Degradação do RNAm Mediada por Códon sem Sentido/genética , RNA Helicases/genética , RNA Mensageiro/sangue , Transativadores/genética , Cafeína/administração & dosagem , Coroideremia/sangue , Coroideremia/genética , Coroideremia/fisiopatologia , Códon sem Sentido/genética , Fibroblastos/efeitos dos fármacos , Fibroblastos/metabolismo , Regulação da Expressão Gênica/efeitos dos fármacos , Genótipo , Humanos , Masculino , Pessoa de Meia-Idade , Mutação/genética , Degradação do RNAm Mediada por Códon sem Sentido/efeitos dos fármacos , Oxidiazóis/administração & dosagem , Fenótipo , Células-Tronco Pluripotentes/metabolismo , RNA Interferente Pequeno/genética , RNA Interferente Pequeno/uso terapêutico , Epitélio Pigmentado da Retina/efeitos dos fármacos , Epitélio Pigmentado da Retina/metabolismoRESUMO
Purpose: To confirm whether choroideremia (CHM) is a systemic disease characterized by blood lipid abnormalities and crystals found in, or associated with, circulating peripheral blood cells of patients. Methods: Peripheral blood samples obtained from three subjects with confirmed mutations in the CHM gene and three age-matched normal controls were processed for transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Fatty acids from plasma of nine male CHM subjects were analyzed and compared to reference values for a sample from a Canadian population. Results: Intracellular crystals were not observed in the cells from choroideremia-affected males. No crystals were found adherent to the external plasma membrane of red blood cells. Fatty acid profiles of patients were similar to reference values, with the exception of lower levels of nervonic acid. Conclusions: This investigation failed to observe crystals previously reported in peripheral circulating blood cells derived from CHM subjects, and showed no significant fatty acid abnormalities, not supporting the view of CHM as a systemic disease.
Assuntos
Coroideremia/sangue , Inclusões Eritrocíticas/ultraestrutura , Membrana Eritrocítica/ultraestrutura , Fosfolipídeos/sangue , Proteínas Adaptadoras de Transdução de Sinal/genética , Adolescente , Adulto , Idoso , Criança , Coroideremia/genética , Coroideremia/patologia , Cristalização , Humanos , Masculino , Microscopia Eletrônica de Varredura , Microscopia Eletrônica de Transmissão , Pessoa de Meia-Idade , Mutação , Adulto JovemRESUMO
PURPOSE: The authors present a case of the 66-year-old female patient suffering from the diffuse atrophy of the choroid. MATERIAL AND METHODS: The 66-year-old woman was referred to the Ophthalmological Clinic in Krakow with the diagnosis of choroideremia. The patient developed central vision problems (mainly in the left eye) and night blindness. We performed following investigations: distance and near visual acuity with Snellen charts, Amsler grid test, the investigation of the anterior and posterior segments of both eyes, and the fluorescein angiography as well as the infrared photo of the fundus. The assessment of ornithine serum level was performed. RESULTS: The ophthalmological examination revealed: the distance visual acuity in the RE=0.5, and in the LE=0.25. The near visual acuity in the RE=0.5, in the LE=0.75. The Amsler grid test in the RE showed no pathology but in the LE revealed in the nasal aspect of the central visual field a relative scotoma. Fundoscopy, fluorescein angiography and infrared imaging revealed the broad patch form atrophy of the RPE and choriocapillaris within the whole fundus and also within the macula. The serum level of ornithine was within the normal limits. CONCLUSIONS: Based on the results of performed investigations the definitive diagnosis of a very rare dystrophy--a diffuse atrophy of the choroid was established.