HNMT and Tatton-Brown-Rahman overgrowth syndrome: Tatton-Brown–Rahman syndrome (TBRS) is caused by a mutation in DNMT3A, a gene that is also associated with Sotos syndrome, which is caused by haploinsufficiency of NSD1, an HMT that catalyzes the demethylation of histone H3 at K36 (H3K36m22).