Constitutional mismatch repair (MMR) deficiency (CMMRD) is a tumour predisposition syndrome that shares some clinical features with NF1, and both syndromes are associated with the occurrence of café-au-lait spots, but also high-grade glioma, acute myeloid leukaemia or rhabdomyosarcoma [44]. The gene discussed is NF1; the disease is Few cafe-au-lait spots.