The purpose of this study is to find blood plasma based biomarkers of disease progression in neurofibromatosis type 1 (NF1). NF1 is associated with the development of benign cutaneous tumors as well as a variety of malignancies. Analysis of plasma DNA and chemical composition may provide tools for diagnosis and follow-up of NF1. The hypothesis of the study is that NF1-associated tumor burden and malignant transformation of tumors can be detected in plasma. To test this hypothesis, Finnish patients with NF1 are recruited and blood sample is taken. Blood plasma is separated and analyzed chemically. DNA is then also extracted and quantified.