CDKN1B and Leigh syndrome: This is supported by evidence (1) that the expression of tumour suppressors p16IINK4 and p27Kip1 is downregulated in LS and (2) that a biomarker of oxidative stress, 8-hydroxy-deoxy-guanosine, increases as LS progresses into neoplasia, although this study30 was undertaken in vulvar LS only.