Monozygotic Twins With Neurofibromatosis Type 1 (NF1) Display Differences in Methylation ofNF1Gene Promoter Elements, 5' Untranslated region, Exon and Intron 1

Abstract

Neurofibromatosis type 1 (NF1) is a common autosomal dominant disorder caused by heterozygotic inactivation of the NF1 tumor suppressor gene at 17q11.2. The associated phenotypes are highly variable, and modifying genes have been proposed to explain at least in part the intriguing expressivity. Given that haploinsufficiency of the NF1 gene product neurofibromin is responsible for some of the clinical manifestations, variations in expression of the wildtype NF1 allele might modify the phenotype. We therefore investigated epigenetic molecular modifications that could result in variable expression of the normal NF1 allele. To exclude confounding by DNA sequence variations, we analyzed monozygotic twin pairs with NF1 who presented with several discordant features. We fine-mapped the methylation pattern of a nearly 1 kb NF1 promoter region in lymphocytes of 8 twin pairs. All twin pairs showed significant intra-pair differences in methylation, especially of specific promoter subregions such as 5'UTR, exon 1 and intron 1 (+7 to +622), transcription factor binding sites and promoter elements like NF1HCS. Furthermore, we detected significant intra-pair differences in cytosine methylation for the region from -249 to -234 with regard to discordance for optic glioma with a higher grade of methylation in glioma cases. In conclusion, our findings of epigenetic differences of the NF1 promoter in leukocytes within mono zygotic twin pairs may serve as a proof of principle for other tissues. The results point towards a role of methylation patterns of the normal NF1 allele for expression differences and for modification of the NF1 phenotype.

Construction and analysis of the protein-protein interaction networks for schizophrenia, bipolar disorder, and major depression

“…In major depression, APP interacted with the abnormally expressed NF1. NF1 encodes a neurofibromin responsible for signal transduction, and has been associated with mental retardation and autism [52,94,95]. APP has been listed in the HGMD as being associated with schizophrenia [96].…”

TAGLN expression is upregulated in NF1-associated malignant peripheral nerve sheath tumors by hypomethylation in its promoter and subpromoter regions

“…A methylation study on the monozygotic twin pairs with NF1 that presented with several discordant features indicated that differences in the methylation patterns of the normal NF1 allele in twins may result in NF1 expression difference, thereby causing a modification of the NF1 phenotype (42). Comparing NF1 patients with a low number of cutaneous neurofibromas to those with a high number of cutaneous neurofibromas, using methylation-specific PCR and pyrosequencing, indicated that the promoter methylation of the mismatch repair MSH2 gene in the blood cells of patients was significantly different (43).…”

Epigenetics in Twin Studies

“…In addition, a pair of leukaemia-discordant twins has been described, in which the affected twin had a constitutive increase in methylation of BRCA1 (breast cancer 1, early onset) [64]. Similarly, in a pair of twins with the autosomal dominant neurofibromatosis type 1 (NF1), phenotypic severity was found to correlate with the level of methylation at the NF1 gene in lymphocytes [65]. Recently, a female twin pair was described in which both twins exhibited symptoms of Rett syndrome, an X-linked neurodevelopmental disorder, with only one twin meeting the full diagnostic criteria [66].…”