MTHFR and Williams syndrome: These conditions include the following: Williams-Beuren syndrome, a disorder caused by a hemizygous deletion in a region of chromosome 7q11.23; hyperhomocysteinemia, due to loss-of-function variants in cystathionine-β-synthase (CBS) or methylenetetrahydrofolate reductase (MTHFR) genes; pseudoxanthoma elasticum (caused by defects in ABCC6); Hutchinson-Gilford progeria syndrome (HGPS) due to overexpression of progerin, a truncated form of lamin A; and Werner syndrome due to pathogenic variants in RECQL2 (9, 48–51).