How could you get neurofibromatosis without it being in your past family genetics?

Mutation. 50% of new NF1 cases are mutations and do not arise from inheritance. NF1 has autosomal dominant inheritance.Descendants of an affected individual have 50% risk of inheriting the altered NF1 gene.
New mutation. Although this is well known to be transmitted as a dominant mutation, as many as 30% represent mew mutations in the patient.