RNMT and Williams syndrome: Catalysis is executed by RNA guanine-7 methyltransferase (RNMT) for the mRNA 5' cap during maturation47, by the METTL1-WDR4 complex internally in tRNAs/miRNAs to prevent cleavage and ensure stability, and by the Williams-Beuren syndrome chromosome region 22 (WBSCR22)/tRNA methyltransferase 112 (TRMT112) complex at specific 18S rRNA sites for ribosomal 40S subunit biogenesis48.