a VNTR located approximately 1.2 kb upstream from the MAOA start codon and within the gene's transcriptional control region123 (see Fig. 11B). Alleles at this VNTR have a different number of tandem copies of a 30-bp sequence, with the three- and four-repeat alleles being by far the most common. Alleles with four repeats are transcribed more efficiently than alleles with three copies, leading to higher MAOA enzyme activity.123
