NF1 and neurofibroma: Also, key observations in a mouse model of NF1 show that tumors only developed in a heterozygous (Nf1+/−) background, implicating other Nf1+/− cell types in neurofibroma formation and Nf1 loss of heterozygosity (LOH) in the Schwann cell lineage is necessary, but not sufficient, to elicit neurofibromas [65], [66].