In this family, the p.Leu790Phe variant was found in nine individuals, four of whom developed MTC; intriguingly, three of these individuals were also affected by neurofibromatosis 1 (NF1), caused by a mutation of the NF1 gene inherited from the other parental branch, and one developed a PCC. Here, NF1 is linked to medullary thyroid gland carcinoma.