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.

Cognitive impairment is a common phenomenon in children with neurofibromatosis type 1 (NF1), but only little is known about its nature and frequency in adult NF1-patients. Using a comprehensive psychometric test battery, we investigated 20 patients with NF1 and 20 age and gender matched control subjects without neurological diseases. Results showed slightly lowered test scores in patients compared with controls but no specific intellectual impairment. On a computerized test of selective attention, the NF1-group had significant slower reaction times. Also, three out of four memory tests and a test of visuoconstructive abilities showed poorer test results in the NF1-patients. Executive functions however were not affected. The findings agreed well with the test profile in NF1-children and supported the idea of a continuum between childhood and adulthood. Observations are discussed in the context of studies investigating the association of cognitive deficits with either intracranial lesions or alterations in the neurofibromin expression.

No abstract

No abstract