Microsatellite instability (MSI) has also been associated with peripheral nerve NF1 tumours, both benign and malignant [16,19] Malignant tumours present higher levels of MSI than benign ones and these findings suggest that mismatch repair genes (MMR) may also participate in the malignant transformation of NF1-associated tumours [20,21]. The gene discussed is MRC1; the disease is cancer.