NF1 and Leigh syndrome: Heterozygous loss-of-function (LoF) variants in SPRED1 underlie Legius syndrome (LS, MIM: 611431) [3], a disorder having some similarities to neurofibromatosis type I (NF1, MIM: 162200) [4], which is caused by inactivating heterozygous mutations in NF1 (MIM: 613113) [5], the gene encoding neurofibromin [6].