Mechanism of somatic NF1 inactivation. (A) Immunohistochemistry using rabbit polyclonal neurofibromin antibodies demonstrates positive immunoreactivity in the normal human brain (HBr). (Inset) Single neuron with neurofibromin expression. In each of the three NF1-PA specimens, no neurofibromin expression was detected. Scale bars, 100 μm. Magnification, 400×. Inset, 600×. (B) In T03, a somatic copy-neutral LOH of the q arm of chromosome 17 from position 23.9 Mbp to the telomere results in duplication of the NF1 W1662* germline variant. Shown are the median variant allele frequencies of high-confidence germline heterozygous SNPs identified in the normal DNA in 100,000-bp bins across chromosome 17. The position of the NF1 gene is indicated. (C) Methylation changes in T01 relative to T02 and T03 from Illumina Infinium HumanMethylation450 arrays for 42 probes spanning the NF1 genomic region. T01 exhibits increased methylation (>2 standard deviations) at NCBI 36 chr17:26648522 (probe cg13759778). This location is within 200 bp of the transcription start site of OMG, one of three antisense nested genes within intron 36 of NF1 mRNA NM_001042492.2.
