Relaxation of imprinting of IGFII gene in juvenile nasopharyngeal angiofibromas.

IGFII and H19 genes are expressed only from one allele due to genomic imprinting, biallelic expression (loss of imprinting) being associated with the tumorigenic process of different types of tumors. The mechanism responsible for genomic imprinting is not yet determined, although DNA methylation has been considered the main genetic event for an imprinted mark. In the current study, the authors analyzed the imprinting status and expression levels of the IGFII and H19 genes in 27 cases of Juvenile Nasopharyngeal Angiofibroma (JNA) using RFLPs, RT-PCR, and Southern and Northern Blots. The authors found that four out of eight informative cases (50%) for ApaI/IFGII polymorphism showed biallelic expression of IFGII whereas none of the nine informative cases for the polymorphism showed biallelic expression of the H19 gene. Overexpression of IFGII was observed in 8 out of 22 cases (36.4%), and 7 out of 19 cases (36.8%) showed H19 overexpression. Hypomethylation was found only in the H19 gene in six out of eight cases analyzed. Therefore, our results demonstrate that alterations in the IFGII/H19 imprinted region occur in JNA.