Antisociality, substance dependence, and the DRD5 gene: a preliminary study

A pilot population-based study of a microsatellite polymorphism at the DRD5 locus in adult European-Americans showed its association with childhood symptom counts for oppositional defiant disorder (ODD) in males and females and adult antisocial personality disorder (ASPD) in females. No association with childhood conduct disorder symptom count was observed. ODD mediated the genotype-ASPD relationship in females. Neither ODD nor ASPD significantly mediated the relationship between the genotype and the liability to substance dependence (SD). The data suggest involvement of the DRD5 locus in the variation and sexual dimorphism of SD liability and antisociality and in the developmental continuity of antisociality.     

Allelic association analysis of the dopamine D2, D3, 5‐HT2A,and GABAAγ2 receptors and serotonin transporter genes with heroin abuse in Chinese subjects

Five candidate genes, the receptors DRD2, DRD3, HTR2A and GABA_Aγ2, and the serotonin transporter (5‐HTT) were analyzed for association with heroin abuse. We examined three polymorphisms (promoter ? 141ΔC, Ser311Cys, and TaqI) in the DRD2 gene, one polymorphism (Ser9Gly) in the DRD3 gene, two polymorphisms (promoter ? 1438G/A and T102C) in the HTR2A gene, two polymorphisms (VNTR and Del/Ins) in 5‐HTT gene, and one polymorphism (G3145A) in GABA_Aγ2 gene in 121 Chinese heroin addicts and 194 controls. None of the polymorphisms differed significantly for allele, genotype, or haplotype frequencies, except for the DRD2 promoter polymorphism ? 141ΔC (genotype‐wise and allele‐wise, P = 0.05, uncorrected). An additional 344 subjects with heroin abuse and 104 controls were investigated for the ? 141ΔC polymorphism. In the second sample, there were no significant difference of genotype or allele frequencies between subjects with heroin abuse and normal controls. When we divided the sample by route of administration into nasal inhalers and IM or IV injectors, however, it produced a significant difference between inhalers of heroin and controls (genotype‐wise, P = 0.006, allele‐wise, P = 0.016) but not for injectors of heroin (genotype‐wise, P = 0.81, allele‐wise, P = 0.69). We also found that LD between all polymorphisms we examined in the gene was weak, possibly explaining why we see association of this polymorphism with heroin abuse but not with other markers in the gene. Overall our results indicates that the HTR2A, 5‐HTT, DRD3 and GABA_Aγ2 genes are not likely to be a major genetic risk factor for heroin abuse in this population, with the exception of possible association between nasal inhalation and DRD2 promoter ? 141ΔC polymorphism. © 2002 Wiley‐Liss, Inc.     

Association between the DRD2 A1 allele and opium addiction in the Iranian population.

Dysfunction of the central dopaminergic neurotransmission has been suggested to play an important role in the etiology of certain neuropsychiatric disorders such as drug abuse. It has been shown that the dopamine D2 receptor (DRD2) gene dysfunction is associated with multi-drug addiction. Addiction to opium is the most common form of drug abuse in Iran. We studied the allelic association between DRD2 Taq I A polymorphism in 100 opium-dependent Iranian patients and 130 unrelated controls. A 310 bp (base pair) region surrounding Taq I site at the DRD2 locus was amplified by polymerase chain reaction (PCR) and the PCR product was incubated with Taq I restriction enzyme. The A1 allele remained intact while the A2 allele was cut. Significant association was observed between A1 allele and addiction in the patients group (P < 0.0001). Moreover, the frequency of A1A1 genotype was significantly higher in opium users than controls (P < 0.0001). Our result indicates that DRD2 might be involved in the pathophysiology of opium addiction.     

Association between polymorphisms of DRD2 and DRD4 and opioid dependence: Evidence from the current studies

Several studies have assessed the association between genetic polymorphisms of DRD2 and DRD4 genes and opioid dependence risk, while the results were inconsistent. We performed a meta‐analysis, including 6,846 opioid dependence cases and 4,187 controls from 22 individual studies, to evaluate the roles of four variants (DRD2 ?141ins/delC, rs1799732; DRD2 311 Ser > Cys, rs1801028; DRD2‐related TaqI A, rs1800497 and DRD4 exon III VNTR) in opioid dependence for the first time. We found that the ?141delC polymorphism was significantly associated with increased risk of opioid dependence (homozygote comparison: odds ratios [OR], 2.71; 95% confidence interval [CI], 1.74–4.22; dominant comparison: OR, 1.27; 95% CI, 1.09–1.48). Similarly, the TaqI A1 polymorphism was also significantly increased opioid dependence risk (homozygote comparison: OR, 2.06; 95% CI, 1.25–3.42; dominant comparison: OR, 1.34; 95% CI, 1.08–1.67). Moreover, long allele (≥5‐repeat) and 7‐repeat allele of DRD4 exon III VNTR were found to be associated with significantly increased opioid dependence risk (OR, 1.50; 95% CI, 1.24–1.80 and OR, 1.57; 95%, 1.18–2.09, respectively). However, no association was detected between the DRD2 311 Ser > Cys polymorphism and opioid dependence. In conclusion, our results suggested that DRD2 ?141ins/delC, DRD2‐related TaqI A and DRD4 exon III VNTR polymorphisms might play important roles in the development of opioid dependence. © 2011 Wiley‐Liss, Inc.     

Studies of the 48 bp repeat polymorphism of the DRD4 gene in impulsive,compulsive, addictive behaviors: Tourette syndrome,ADHD, pathological gambling,and substance abuse

Prior studies have reported an association between the presence of the 7 repeat allele of the 48 bp repeat polymorphism of the third cytoplasmic loop of the dopamine D4 receptor gene (DRD4) and novelty seeking behaviors, attention deficit hyperactivity disorder (ADHD), Tourette syndrome (TS), pathological gambling, and substance abuse. However, other studies have failed to replicate some of these observations. To determine whether we could replicate these associations we genotyped 737 individuals from four different groups of control subjects, and 707 index subjects from four different groups of impulsive, compulsive addictive behaviors including substance abuse, pathological gambling, TS, and ADHD. Chi-square analysis of those carrying the 7 allele versus non-7 allele carriers was not significant for any of the groups using a Bonferroni corrected α of .0125. However, chi-square analysis of those carrying any 5 to 8 allele versus noncarriers was significant for pathological gambling (p < .0001), ADHD (p ⩽ .01) and the total index group (p ⩽ .0004). When the comparison included all 7 alleles the results were significant for gamblers (p < .0001), TS (p ⩽ .003), ADHD (p ⩽ .003), and the total group (p ⩽ .0002). There was a significant increase in the frequency of heterozygosity versus homozygosity for all alleles for pathological gamblers (p ⩽ .0031) and the total index group (p ⩽ .0015), suggesting that heterosis played a role. In the substance abuse subjects a quantitative summary variable for the severity of drug dependence, based on the Addiction Severity Index, showed that the scores varied by increasing severity across the following genotypes: 44 ⩽ heterozygotes ⩽ 77 ⩽ 22. Studies of other quantitative traits indicated an important role for the 2 allele and the 22, 24, and 27 genotypes. All studies indicated that the role of the DRD4 gene in impulsive, compulsive, addictive behaviors is more complex than a sole focus on the 7 versus non-7 alleles. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 88:358–368, 1999. © 1999 Wiley-Liss, Inc.     

The D2 dopamine receptor gene: A review of association studies in alcoholism

Following our initial observation that theAl allele of the D₂ dopamine receptor (DRD2) gene was associated with alcoholism, a number of studies, both in the United States and abroad, have attempted to replicate and extend this finding in different Caucasian populations. In nine independent studies containing a total of 491 heterogeneous alcoholics (less severe and severe) and 495 heterogeneous controls (assessed and unassessed for alcoholism), the prevalence of theAl allele was 43.0% in the former group compared to 25.7% in the latter group (odds ratio=2.18, p<10^–7). The prevalence of theAl allele increased to 56.3% in a more homogeneous sample of 158 severe alcoholics (odds ratio =3.32,p<10^–8). Moreover, theBl allelle of theDRD2 gene was also found to be significantly associated with severe alcoholism. Additional data are accruing which also implicate theDRD2 Al andBl alleles in substance use disorders other than alcoholism. If further studies continue to support the results currently at hand, they would indicate that theDRD2 gene is the most prominent single gene determinant of susceptibility to severe substance abuse. However, the larger role still appears to be played by a combination of environmental factors and as yet unidentified genes.     

Preliminary evidence for an association of a dinucleotide repeat polymorphism at the MAOA gene with early onset alcoholism/substance abuse

An association between the liability to early onset alcoholism/substance abuse and a recently discovered dinucleotide repeat length polymorphism at the MAOA gene (MAOCA-1) was examined using polymerase chain reaction (PCR). A significant correlation between the presence/absence of the disorder and the length of the MAOCA-1 repeat was found in males, but not females, with “long” alleles (repeat length above 115 bp) associated with both increased risk for the disorder and lower age of onset of substance abuse. These preliminary data suggest that further exploration of the relationship between the MAOA gene and behavioral traits in an expanded sample is warranted. © 1995 Wiley-Liss, Inc.     

Studies of the 48 bp repeat polymorphism of the DRD4 gene in impulsive, compulsive, addictive behaviors: Tourette syndrome, ADHD, pathological gambling, and substance abuse.

Prior studies have reported an association between the presence of the 7 repeat allele of the 48 bp repeat polymorphism of the third cytoplasmic loop of the dopamine D4 receptor gene (DRD4) and novelty seeking behaviors, attention deficit hyperactivity disorder (ADHD), Tourette syndrome (TS), pathological gambling, and substance abuse. However, other studies have failed to replicate some of these observations. To determine whether we could replicate these associations we genotyped 737 individuals from four different groups of control subjects, and 707 index subjects from four different groups of impulsive, compulsive addictive behaviors including substance abuse, pathological gambling, TS, and ADHD. Chi-square analysis of those carrying the 7 allele versus non-7 allele carriers was not significant for any of the groups using a Bonferroni corrected alpha of.0125. However, chi-square analysis of those carrying any 5 to 8 allele versus noncarriers was significant for pathological gambling (p <.0001), ADHD (p 相似文献   

DRD4 dopamine receptor genotype and CSF monoamine metabolites in Finnish alcoholics and controls

The DRD4 dopamine receptor is thus far unique among neurotransmitter receptors in having a highly polymorphic gene structure that has been reported to produce altered receptor functioning. These allelic variations are caused by a 48-bp segment in exon III of the coding region which may be repeated from 2–10 times. Varying the numbers of repeated segments changes the length, structure, and, possibly, the functional efficiency of the receptor, which makes this gene an intriguing candidate for variations in dopamine-related behaviors, such as alcoholism and drug abuse. Thus far, these DRD4 alleles have been investigated for association with schizophrenia, bipolar disorder, Parkinson's disease, and chronic alcoholism, and all have been largely negative for a direct association. We evaluated the DRD4 genotype in 226 Finish adult males, 113 of whom were alcoholics, many of the early onset type with features of impulsivity and antisocial traits. Genotype frequencies were compared to 113 Finnish controls who were free of alcohol abuse, substance abuse, and major mental illness. In 70 alcoholics and 20 controls, we measured CSF homovanillic acid (HVA), the major metabolite of dopamine, and 5-hydroxyindoleacetic acid (5-HIAA). No association was found between a particular DRD4 dopamine receptor allele and alcoholism. CSF concentrations of the monoamine metabolites showed no significant difference among the DRD4 genotypes. This study of the DRD4 dopamine receptor in alcoholics is the first to be conducted in a clinically and ethnically homogeneous population and to relate the DRD4 genotype to CSF monoamine concentrations. The results indicate that there is no association of the DRD4 receptor with alcoholism. © 1995 Wiley-Liss, Inc.     

The interaction of DRD2 and violent victimization on depression: an analysis by gender and race

BackgroundRecent research has shown that a polymorphism in the dopamine D2 receptor gene (DRD2) moderates the association between stressful life events and depression. The present study builds off this literature and examines whether DRD2 moderates the effect of violent victimization on depression. Furthermore, the current analyses investigate whether the effects of DRD2 and violent victimization vary by gender and by race for females.MethodsRespondents from waves II and III of the National Longitudinal Study of Adolescent Health (Add Health) completed questionnaires regarding their depressive symptoms and violent victimization experiences (n = 2380).ResultsMultivariate regression results reveal that violent victimization has a strong independent effect on depressive symptoms for Caucasian females. In contrast, violent victimization is only associated with higher levels of depressive symptoms among African American females when they carry at least one A1 allele of DRD2. Results also show that DRD2 has a significant independent effect on depressive symptoms for males and African American females.ConclusionsThe results suggest that African American females who carry the A1 allele of DRD2 may be more vulnerable to the negative effects of violent victimization than African American females who do not carry at least one copy of the A1 allele.LimitationsThe current study's findings may not generalize to clinical populations, adults, and individuals residing in other countries. In addition, the effects of DRD2 may reflect other polymorphisms that are in linkage with DRD2.     

High-activity catechol-O-methyltransferase allele is more prevalent in polysubstance abusers

Allelic variants at the catechol-O-methyl-transferase (COMT) locus are candidates to contribute to genetic components of interindividual differences in vulnerability to substance abuse. COMT plays a prominent role in dopaminergic circuits important for drug reward, and COMT alleles encode enzymes whose activities vary from three- to four-fold. We compared COMT allele frequencies in control research volunteers reporting insignificant lifetime use of addictive substances with those in volunteers reporting substantial polysubstance use. Homozygosity for the high-activity COMT allele was found in 18% of controls, 31% of volunteers with high lifetime substance use, and 39% meeting DSMIII-R substance abuse criteria [odds ratio (relative risks) 2.0 (control vs. use; 95% confidence interval 1.2-3.5; P < 0.013) and 2.8 (control vs. DSM; 1.3-6.1; P < 0.008)]. Individuals with the high-activity COMT variant may have greater genetic vulnerability to drug abuse. Am. J. Med. Genet. 74:439–442, 1997. © 1997 Wiley-Liss, Inc.     

Male limited association of the dopamine receptor D2 gene TaqI a polymorphism and alcohol dependence

Association studies of the TaqI A allele of the dopamine receptor D2 (DRD2) gene with alcohol dependence have produced conflicting findings. Although a wide series of clinical features have been considered in the different association studies performed, very few studies specifically analyzed the role of gender. We compared the TaqI A polymorphisms of the DRD2 gene in 120 French Caucasian alcohol-dependent inpatients (62 males and 58 females) and 107 healthy ethnically matched controls (66 males and 41 females). We observed that 55% of alcohol-dependent males have at least one A1 allele, a prevalence that is significantly above that observed in the control males (38%). On the contrary, no differences were found in females between the alcohol-dependent inpatients and controls for the A1 allele prevalence. In our sample, this male-specific association was not explained by gender specificities of alcohol dependence, such as age at onset and severity measures (mean numbers of social, somatic, and withdrawal complications). On the other hand, alcohol-dependent women with the A1 allele reported more frequently a major depressive disorder (70% vs. 40%, P = 0.03). We thus replicated the allelic association of the A1 allele of the DRD2 gene with alcohol dependence, but showed a male-limited effect of this "vulnerability allele." Recent evidence for gender difference in dopamine D2-like receptor levels and affinity may explain this discrepancy.     

Imaging gene–substance interactions: The effect of the DRD2 TaqIA polymorphism and the dopamine agonist bromocriptine on the brain activation during the anticipation of reward

Dopamine is known as the main neurotransmitter modulating the activation of the reward system of the brain. The DRD2 TaqIA polymorphism is associated with dopamine D2 receptor density which plays an important role in the context of reward. Persons carrying an A1 allele have a lower D2 receptor density and a higher risk to show substance abuse. The present study was designed to investigate the influence of the DRD2 TaqIA polymorphism and the selective D2 receptor agonist bromociptine on the activation of the reward system by means of functional magnetic resonance imaging (fMRI). In a double-blind crossover study with 24 participants we found an increase of reward system activation from placebo to bromocriptine only in subjects carrying the A1 allele. Furthermore, only A1 carrier showed an increase of performance under bromocriptine. The results are interpreted as reflecting a specific sensitivity for dopamine agonists in persons carrying an A1 allele and may complement actual data and theories of the development of addiction disorders postulating a higher genetic risk for substance abuse in carrier of the A1 allele.     

A functional polymorphism in the promoter region of the dopamine D2 receptor gene is associated with schizophrenia

An excess dopaminergic activity may be implicated in the etiology of schizophrenia. Our objective was to identify nucleotide variants in the 5' region of the dopamine D2 receptor gene (DRD2) and to clarify their effects on schizophrenia. We identified two polymorphisms, the A-241G and -141C Ins/Del, by examination of 259 bp in the 5'-flanking region and 249 bp of exon 1 of DRD2. Reporter constructs containing the -141C Del allele cloned into a luciferase reporter plasmid drove 21% (Y-79 cells) and 43% (293 cells) expression compared with the -141C Ins allele. In a case-control study, the -141C Del allele frequency was significantly lower in 260 schizophrenic patients than in 312 controls (OR = 0.60, 95%CI 0.44-0.81, P < 0.001). No significant association was found between the A-241G polymorphism and in vitro luciferase activity, or in allele frequency between the patients versus controls. These findings show that the -141C Ins/Del may be a functional polymorphism in the 5'-promoter region of DRD2 and may affect the susceptibility to schizophrenia.      

Relationship between Taq1 A dopamine D2 receptor (DRD2) polymorphism and prolactin response to bromperidol

The dopamine D2 receptor (DRD2) gene has a Taq1 A restriction fragment length polymorphism yielding two alleles, A1 and A2. We have previously shown that female patients with the A1 allele show greater prolactin response to nemonapride, a selective antagonist for D2-like dopamine receptors, in schizophrenic patients. In the present study, the relationship between this polymorphism and prolactin response to bromperidol was investigated in 32 untreated schizophrenic inpatients (16 males, 16 females). The daily dose of bromperidol was fixed at 6 (n = 10), 12 (n = 13), or 18 mg (n = 9) during a 2-week treatment period. Taq1 A genotypes were determined by PCR method. Plasma prolactin concentration was measured by radioimmunoassay. Plasma concentration of bromperidol was measured by HPLC method. The subjects were divided into four subgroups by gender and the genotypes, i.e., 10 males and 11 females with the A1 allele, 6 males and 5 females with no A1 allele. The females with the A1 allele had the highest Delta prolactin (the change from the pretreatment concentration)/bromperidol concentration ratio among the other groups (P < 0.05). The present study thus suggests that female patients with the A1 allele show greater prolactin response to bromperidol, who may have a high risk for adverse effects associated with neuroleptic-induced hyperprolactinemia.     

Allelic association analysis of the dopamine D2, D3, 5-HT2A, and GABA(A)gamma2 receptors and serotonin transporter genes with heroin abuse in Chinese subjects

Five candidate genes, the receptors DRD2, DRD3, HTR2A and GABA(A)gamma2, and the serotonin transporter (5-HTT) were analyzed for association with heroin abuse. We examined three polymorphisms (promoter - 141DeltaC, Ser311Cys, and TaqI) in the DRD2 gene, one polymorphism (Ser9Gly) in the DRD3 gene, two polymorphisms (promoter - 1438G/A and T102C) in the HTR2A gene, two polymorphisms (VNTR and Del/Ins) in 5-HTT gene, and one polymorphism (G3145A) in GABA(A)gamma2 gene in 121 Chinese heroin addicts and 194 controls. None of the polymorphisms differed significantly for allele, genotype, or haplotype frequencies, except for the DRD2 promoter polymorphism - 141DeltaC (genotype-wise and allele-wise, P = 0.05, uncorrected). An additional 344 subjects with heroin abuse and 104 controls were investigated for the - 141DeltaC polymorphism. In the second sample, there were no significant difference of genotype or allele frequencies between subjects with heroin abuse and normal controls. When we divided the sample by route of administration into nasal inhalers and IM or IV injectors, however, it produced a significant difference between inhalers of heroin and controls (genotype-wise, P = 0.006, allele-wise, P = 0.016) but not for injectors of heroin (genotype-wise, P = 0.81, allele-wise, P = 0.69). We also found that LD between all polymorphisms we examined in the gene was weak, possibly explaining why we see association of this polymorphism with heroin abuse but not with other markers in the gene. Overall our results indicates that the HTR2A, 5-HTT, DRD3 and GABA(A)gamma2 genes are not likely to be a major genetic risk factor for heroin abuse in this population, with the exception of possible association between nasal inhalation and DRD2 promoter - 141DeltaC polymorphism.     

Overlapping Dopaminergic Pathway Genetic Susceptibility to Heroin and Cocaine Addictions in African Americans

Drugs of abuse activate the mesolimbic dopaminergic pathway. Genetic variations in the dopaminergic system may contribute to drug addiction. Several processes are shared between cocaine and heroin addictions but some neurobiological mechanisms may be specific. This study examined the association of 98 single nucleotide polymorphisms in 13 dopamine‐related genes with heroin addiction (OD) and/or cocaine addiction (CD) in a sample of 801 African Americans (315 subjects with OD ± CD, 279 subjects with CD, and 207 controls). Single‐marker analyses provided nominally significant evidence for associations of 24 SNPs) in DRD1, ANKK1/DRD2, DRD3, DRD5, DBH, DDC, COMT and CSNK1E. A DRD2 7‐SNPs haplotype that includes SNPs rs1075650 and rs2283265, which were shown to alter D2S/D2L splicing, was indicated in both addictions. The Met allele of the functional COMT Val158Met was associated with protection from OD. None of the signals remained significant after correction for multiple testing. The study results are in accordance with the results of previous studies, including our report of association of DRD1 SNP rs5326 with OD. The findings suggest the presence of an overlap in genetic susceptibility for OD and CD, as well as shared and distinct susceptibility for OD in subjects of African and European descent.     

精神分裂症与六种候选功能基因的关联研究

目的：探讨多巴胺D2受体基因（dopamine D2 receptor,DRD2)、多巴胺D4受体基因（DRD4）、5－羟色胺2A受体基因（5－hydroxytryptamine 2A receptor,5-HT2A),5-羟色胺6受体基因（5－HT6)、儿茶酚胺氧位甲基转移酶基因（catechol-O-methyltransferase,COMT)和多巴胺转运体基因（dopamine transferase,DAT1)多态性与精神分裂症的关系。方法：应用基因扩增片段长度多态和基因扩增的限制性片段长度多态技术，对中国汉族人群中67例精神分裂症患者与上述6种候选功能和基因扩增的限制性片段长度多态技术，对中国汉族人群中67例精神分裂症患者与上述6种候选功能基因进行遗传关联分析。结果：（1）DRD2、5－HT2A、5－HT6和KCOMT的基因型和等位基因频率在患者组和对照组中差异无显著性（P＞0．05）。（2）DRD4基因中6次重复序列等位基因、DAT1基因中480bp等位基因和480／520基因型在两组中差异有显著性，Z分别为2．03、2．05和2．05；P均小于0．05。（3）经关联分析后，仅DAT1基因的480bp等位基因的比值比为0．441，95％可信区间为0．202－0．963，并有显著性意义（Z＝2．05，P＜0．05），而DAT1的480／520基因型和DRD4和6次重复序列等位基因的比值比分别为0．128和0．123，但Z均小于1．96，无显著性意义（P＞0．05）。因此，6个功能基因中仅DAT1的480bp等位基因与精神分裂症呈负关联。结论：中国汉族人群中DAT1基因的480bp等位基因与精神分裂症间存在负关联，支持精神分裂症的多巴胺假说。     

Variation and linkage disequilibrium between a structurally polymorphic Alu located near the OR12D2 gene of the extended major histocompatibility complex class I region and HLA‐A alleles

We investigated the genetic structure and population frequency of an Alu repeat dimorphism (absence or presence) located near the OR12D2 gene within the olfactory receptor gene region telomeric of the alpha HLA class I region (HLA‐J, ‐A, ‐G, ‐F). The structurally polymorphic Alu insertion (POALIN) locus rs33972478 that we designated as AluOR and its allele and haplotype frequencies and association with HLA‐A and six other structurally polymorphic retroelements (3 Alu, 2 SVA and an HERVK9) were determined in 100 Japanese, 174 Caucasians and 100 African American DNA samples. The AluOR insertion varied in population frequency between 14.4% and 31.5% with significant differences between the Japanese and Caucasians, but not between the Caucasian and African Americans. Although AluOR is located 600 kb from the HLA‐A gene, there was a significant linkage disequilibrium between the two loci and a high percentage association of the AluOR insertion with HLA‐A29 (79%) in Caucasians and HLA‐A31 (69.4%) in Japanese. Inferred haplotypes among three‐locus to eight‐locus haplotype structures showed maximum differences between the populations with the eight‐locus haplotypes. The most frequent multilocus haplotype shared between the populations was the HLA‐A2 allele in combination with the AluHG insertion. The AluOR whether investigated alone or together with the HLA class I alleles and other dimorphic retroelements is an informative ancestral marker for the identification of lineages and variations within the same and/or different populations and for examining the linkage and crossing‐over between the HLA and OR genomic regions in the extended MHC.