The 5′ promoter region of the MAOA gene was genotyped by polymerase chain reaction followed by size fractionation, similar to the method described by Sabol (4). Eight percent of subjects were regenotyped for quality control with complete concordance. The MAOA polymorphism consists of 30-bp repeated sequence presented in 2, 3, 3.5, 4, or 5 copies (4). Sabol (4) found that alleles with 3.5 and 4 copies of the repeat sequence were transcribed more efficiently than those with 3 or 5 copies of the repeat; Deckert (5) found that all longer alleles (3.5, 4, and 5 repeats) were transcribed more efficiently than the 3-repeat allele. This discrepancy in findings has resulted in variations in the definition of genetic risk among studies. Only one child in the sample had the 5-repeat allele, and the pattern of findings were comparable whether or not this child was included and whether or not the 5-repeat allele was assigned as “low” or “high” activity. Therefore, in our study, 2, 3, and 5 repeat alleles were classified as “low activity,” and 3.5 and 4 repeat alleles as “high activity.”
