The NF1 gene is located on chromosome 17 and encompasses more than 300 kb of genomic DNA with 60 exons. The protein product is referred to as ''neuro-fibromin,'' a 2818 amino acid protein. Neurofibromin includes a GTPase-activating protein (GAP) domain, which regulates the conversion of Ras-GTP to Ras-GDP. Neurofibromin therefore appears to be a regulator of Rasmediated intracellular signaling. The NF1 gene behaves as a classic tumor suppressor. Affected individuals are heterozygous for NF1 mutations, but both alleles are mutated in tumor cells. The ''tumor cell'' of the neurofibroma is the Schwann cell, but much of the bulk of the lesion consists of other heterozygous cells, including fibroblasts and mast cells, recruited to the lesion by cytokines yet to be identified. Malignant growths are likely to arise from the acquisition of additional genetic changes, such as loss of function of p53. It is unclear whether some of the nontumor manifestations, such as learning disability, also arise from a tumor suppressor mechanism, or whether haploinsufficiency explains any of these lesions.
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The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.