Among children who had a clinical diagnosis of NF1, but tested negative for pathogenic NF1 variations, there were three patients with Legius syndrome (P21–23), two with neurofibromatosis type 2 (NF2) (P24, 25), one with multiple endocrine neoplasia type 2B (MEN2B) (P26), one with LEOPARD syndrome (P27), and one with a 46,XX,inv(4)(p13q13) karyotype (P28). Here, RET is linked to multiple endocrine neoplasia type 2.