DNA alterations occurs frequently in sorne types of neoplasia such as retinoblastoma, and lung, breast and colorectal carcinoma, We have found that loses of restriction fragments at the epidermal growth factor receptor gene (EGEF-R) are present in as much as 82% of human brain tumours. Amplifications of fragments are present at a much lower proportion reaching only 10% of the samples examined. Two fragments of 9kb and 3.6kb are preferentially lost during tumorigenesis and the latter only is not present in 79% of the cases in which normal and tumoral samples from the same individual were compared. In all but one sample examined in which alterations are present, the 3.6kb fragment was heterozygotic in normal tissues and was not present in the tumour. Normal tissue surrounding the tumour was analyzed in a few examples and already showed a certain degree of alteration but normally not as much as the tumour itself. This will suggest that an accumulation ofseveral DNA aberrations might be responsible for determining the tumour biological propertieso Restriction fragment length polymorphism (RFLP), irrelevant to tumorigenesis, was found in about 22% of the cases.
Alteraciones en las cadenas de DNA han sido detectadas en algunos tipos tumorales, como retinoblastomas y carcinomas de pulmón, mama y colon. Por nuestra parte, hemos observado que en el 82% de los tumores cerebrales examinados existen pérdidas de fragmentos de DNA en el gen del receptor del factor de crecimiento epidérmico, así como amplificación de otros fragmentos en el 10% de los tumores. Los fragmentos que más frecuentemente faltan son dos, uno de 9kb (kilobase) y otro de 3,6. Este último no se encontró en el 79% de los casos en los que existía en el tejido normal del mismo paciente. En todos los casos excepto en uno, este fragmento era heterozigoto en el tejido normal y faltaba en el tumoral. El tejido aparentemente normal que rodea al tumor fue analizado en algunos casos, observándose en él algunas anomalías, aunque no tantas como en el propio tumor. Esto sugiere que probablemente sean necesarias varias alteraciones del DNA para que aparezcan las propiedades tumorales. Polimorfismo en la longitud de los fragmentos de restricción fue observado en el 22% de los casos.
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