分子遺傳學的研究指出，人類許多的個性特質受到遺傳基因及環境等多層面因素影響。文獻上也發現多巴胺(dopamine)神經傳導物質與性衝動、攻擊性行為有關係，其中負責代謝分解多巴胺物質的MAO (monoamine oxidase)及COMT (catechol-O-methyltransferase)酶的基因，以及多巴胺受器(dopaminereceptor) 基因上的變異，均可能導致基因功能的喪失或異常，進而影響腦中多巴胺神經傳導物質的高低。性犯罪之發生牽涉到多種層面因素，諸如社會環境
影響、個人心理因素、生物因素等多方面的交互作用，本研究則假設性犯罪行為與某些特定的候選基因是有所關聯的，並從生物因素角度探討實驗組與控制組的差異性，嘗試了解是否有某些特定的基因型組合比較容易產生性侵害行為。實驗組檢體樣本為台北監獄男性性犯罪受刑人，計有265 人；控制組主要為中央警察大學學員生，計有240 人。選擇與行為特質調控有關的基因作為檢測標誌，且均是與多巴胺含量有關係的基因群，共計五個，其中MAOA-uVNTR、MAOA-Fnu4H1、MAOB-SNP 及COMT-RFLP 等四個均屬具有功能的基因標誌(functional markers)，而DRD2-Taq1A 則為單純的DNA 標誌。檢體樣本經抽取DNA、聚合酶連鎖反應複製、特定酵素切割遺傳片段及電泳法分析基因型別後，以卡方檢定分析各候選基因標誌基因型，在實驗組與控制組間分佈情形是否達到統計學上顯著差異(p<0.05)。研究結果：在實驗組與控制組之五個基因標
誌之基因型分佈上，MAOA-uVNTR (x2=12.737, p=0.00065)與MAOA-Fnu4H1(x2=9.38, p=0.002)均達到統計上顯著差異；MAOB-SNP 只在犯二次以上性犯罪行為的累犯組上才有特出的現象，而達到統計上顯著差異(x2=4.494, p=0.034)；其餘二個基因標誌(COMT-RFLP、DRD2-Taq1A)的基因型則在實驗組與控制組均無統計上的差異。其結果意義上的推論為MAOA-uVNTR、MAOA-Fnu4H1、MAOB-SNP 可能在性犯罪行為的產生或促進上扮演著相當程度的角色，在經由
三個基因的單套基因型(haplotype)的比較分析結果發現，MAOA-Fnu4H1、MAOB-SNP 兩個具功能的基因標誌有加強的作用，但是MAOA-uVNTR 卻有著稀釋實驗組與控制組兩群差異的效果，此情況或許由因MAOA-uVNTR 並非是MAOA 基因表現量之主要調控者而得到合理的解釋。

According to the studies of molecular genetics, many characteristics of an
individual have been determined early before being born. Recently, literatures reveal that the neurotransmitter of dopamine is closely associated with human sexual arousal, aggressive and impulsive behavior. The dopamine neurotransmitter would be mainly digested by the genes of COMT (catechol-O-methyltransferase) and MAO (monoamine oxidase), which is divided into two subtypes of MAOA and MAOB. The mutation and/or variations in the genes of MAO, COMT and dopamine receptors (DRD) may cause a change or a loss in genetic functions, influencing the concentration of dopamine in brain, and leading to the development of psychiatric abnormal behaviors. Sexually aggressive behavior has the nature of impulsiveness and violence. The purpose of this study was thus to evaluate the possible association of sexually aggressive
behavior and candidate genes. It was hypothesized that over-expressed dopamine in brain could play a role in susceptibility to the sexually violent behaviors. The association study was performed on the 265 male inmates (sexual offenders) from Taipei Prison and the 240 control subjects, which were the students of Central Police University. Four functional markers of MAOA-uVNTR, MAOA-Fnu4H1,MAOB-SNP, COMT-RFLP, and one DNA marker of DRD2-Taq1A were investigated. After DNA extraction, analyses of polymerase chain reaction (PCR),restriction fragment length polymorphism (RFLP), and electrophoresis were performed on the case and control groups. The data of the genotypic and allelic types from the two groups were analyzed using the chi-square test. The results showed that statistical significance (p<0.05) was observed on genotype and allelic
type of MAOA-uVNTR(x2=12.737, p=0.00065) and MAOA-Fnu4H1(x2=9.38,
p=0.002) between the case and the control group. The significance was also found on the MAOB-SNP between the control and repeatedly sexual criminals (x2=4.494,p=0.034). No significance was seen on the genotype and allele type of the two markers of COMT-RFLP and DRD2-Taq1A. Additionally, the haplotype analyses of the MAOA-Fnu4H1 and MAOB-SNP, but not the MAOA-uVNTR, showed a positive effect on the association. These results implicated that the three functional markers (MAOA-uVNTR, MAOA-Fnu4H1 and MAOB-SNP loci) could play a role in promoting the exhibition of sexually violent behaviors. This study might provide a better understanding for the relationship between sexually violent behaviors and the regulation of the candidate genes.