To determine if the hemizygous deletion resulted in reduced expression of genes mapping within the deleted region, we measured the gene expression levels in peripheral blood leukocytes derived from individuals with 22q11DS of the following six genes: catechol-O-methyltransferase; COMT, DiGeorge syndrome critical region gene 6; DGCR6, DiGeorge syndrome critical region gene 8; DGCR8, zinc finger DHHC-type containing 8; ZDHHC8, thioredoxin reductase 2; TXNRD2, and solute carrier family 25 member 1; SLC25A1 and of one gene, the Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) used as control. This evidence concerns the gene COMT and 22q11.2 deletion syndrome.