Characterization of a highly polymorphic region near the first exon of the human MAOA gene containing a GT dinucleotide and a novel VNTR motif.

The genes encoding the A and B forms of the human monoamine oxidase enzymes (MAOA and MAOB) are localized at Xp11.23-Xp11.4. We report the characterization of a highly informative polymorphic region within a 2.9-kb cloned fragment containing the first exon of the MAOA gene. The polymorphic region consists of a GT microsatellite directly adjacent to an imperfectly duplicated novel 23-bp VNTR motif. DNA sequencing within and flanking the repeated segment allowed the design of specific amplification primers. In 56 unrelated females, 15 different alleles were identified with sizes ranging from 285 to 388 bp. The alleles differed in both the number of dinucleotide and the number of VNTR repeats, yielding a highly informative polymorphic marker locus with a calculated heterozygosity value of 75%.