SCN9A and Lesch-Nyhan syndrome: MiTES can be clinically distinguished from other neurological or infectious causes of chronic itch or repetitive self-mutilating behaviour (e.g. trigeminal trophic syndrome, erythropoietic protoporphyria and Lesch–Nyhan syndrome), from known Mendelian forms of itch (reported with particular mutations in SCN9A, SCN11A and COL6A1),15–17 and can be confirmed by genetic testing.1,2,5 The most frequent genetic finding in MiTES is a homozygous expansion of the PRDM12 polyalanine tract to 18A repeats.