Tuesday, September 13, 2011

Attack of the Warrior Gene Babies!

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The so-called “warrior gene” is the reason babies have tantrums. And you thought it was creamed spinach. Okay, I lied. Actually, the first study on the effects of monoamine oxidase A (MAOA) on infants determined that the 3-repeat allele decreases behavioral regulation in Chinese baby girls. Crying was a controlled factor because it could represent fear rather than baby rage. Behavioral regulation was measured by gaze aversion from a menacing toy gorilla. Believe it or not, the inability to do this is associated with childhood externalizing behaviors like fighting and hitting.

The only significant main effect of MAOA was in the girls, which was fodder for interesting discussion of the gender differences and developmental component of the gene’s expression. MAOA is subject to epigenetic methylation, but mostly just in women. The vast majority of that methylation seems to have already occurred by age 5, according to Wong et al. Increased methylation gives women more symptoms of alcohol and nicotine dependence but not antisocial personality disorder, according to Philibert et al. The warrior gene concerns a VNTR (variable number tandem repeat) promoter, but another study by Philibert et al recently discovered a second VNTR that seems to have a greater effect on antisocial personality disorder in women (but not men) than the heavily studied VNTR, and both VNTR influence MAOA methylation in women. The fact that the sex hormones testosterone and estradiol affect MAOA expression should also enter any thorough discussion of sex differences in the warrior gene. Such increasingly complex factors involved in MAOA expression in women are modifying a long-held view that MAOA does not affect women even when it is completely shut off in Brunner syndrome. Or as Dr. Phil put it, “[the warrior gene] is more rare in women, of course” which is not actually true, but at least he is trying.

Speaking of hormones, over the past decade many studies have examined the effects of testosterone and cortisol on aggression. One study determined that testosterone and cortisol even affect the militancy and aggression of Palestinians. Oddly, this research has never seemed to cross paths with research on the proven effects of testosterone and cortisol on MAOA expression. However, scientists have identified a gene-gene interaction between the androgen receptor and glucocorticoid receptor genes, so these might be violence genes just like MAOA, DAT1, DRD2, DRD4, and 5-HTTLPR.

Getting back to the study on babies, this new data also helps clarify the allele frequencies in Asians. I now count a nearly 1,500 cumulative allele sample size among those Asian subjects, predominantly Chinese, for whom selection bias does not apply, and 54% are the warrior gene, which I consider the three-repeat allele (although the much less common 2-repeat allele is also included under this label). This is not much different from that of African Americans, but nearly five percent of African American men have the more violent 2-repeat allele, compared to only one allele of Asian control subjects in the seven studies that I counted. A 2009 editorial that was included in a series of attacks on MAOA research as a reaction to the Rod Lea/Maori controversy claimed Chinese people have the highest warrior gene allele frequency of any ethnic group. That was based on an uncorrected error in The New Zealand Medical Journal that switched the number of subjects (77) with the percentage with the three-repeat allele (55%) from the study by Lu et al. One would think that researchers who study warriors would be more careful.

Zhang M, Chen X, Way N, Yoshikawa H, Deng H, Ke X, Yu W, Chen P, He C, Chi X, & Lu Z (2011). The association between infants' self-regulatory behavior and MAOA gene polymorphism. Developmental science, 14 (5), 1059-1065 PMID: 21884321

Zhou Q, Hofer C, Eisenberg N, Reiser M, Spinrad TL, & Fabes RA (2007). The developmental trajectories of attention focusing, attentional and behavioral persistence, and externalizing problems during school-age years. Developmental psychology, 43 (2), 369-85 PMID: 17352545

Wong CC, Caspi A, Williams B, Craig IW, Houts R, Ambler A, Moffitt TE, & Mill J (2010). A longitudinal study of epigenetic variation in twins. Epigenetics : official journal of the DNA Methylation Society, 5 (6), 516-26 PMID: 20505345

Philibert RA, Gunter TD, Beach SR, Brody GH, & Madan A (2008). MAOA methylation is associated with nicotine and alcohol dependence in women. American journal of medical genetics. Part B, Neuropsychiatric genetics : the official publication of the International Society of Psychiatric Genetics, 147B (5), 565-70 PMID: 18454435

Philibert RA, Wernett P, Plume J, Packer H, Brody GH, & Beach SR (2011). Gene environment interactions with a novel variable Monoamine Oxidase A transcriptional enhancer are associated with antisocial personality disorder. Biological psychology, 87 (3), 366-71 PMID: 21554924

Victoroff J, Quota S, Adelman JR, Celinska B, Stern N, Wilcox R, & Sapolsky RM (2011). Support for religio-political aggression among teenaged boys in Gaza: part II: neuroendocrinological findings. Aggressive behavior, 37 (2), 121-32 PMID: 21274850

Chen S, Wang J, Yu G, Liu W, & Pearce D (1997). Androgen and glucocorticoid receptor heterodimer formation. A possible mechanism for mutual inhibition of transcriptional activity. The Journal of biological chemistry, 272 (22), 14087-92 PMID: 9162033

Sue Z. Sabol, Stella Hu, & Dean Hamer (1998). A functional polymorphism in the monoamine oxidase A gene promoter Human Genetics, 103 (3), 273-279 : 10.1007/s004390050816

Ono H, Shirakawa O, Nishiguchi N, Nishimura A, Nushida H, Ueno Y, & Maeda K (2002). No evidence of an association between a functional monoamine oxidase a gene polymorphism and completed suicides. American journal of medical genetics, 114 (3), 340-2 PMID: 11920860

Lu RB, Lee JF, Ko HC, Lin WW, Chen K, & Shih JC (2002). No association of the MAOA gene with alcoholism among Han Chinese males in Taiwan. Progress in neuro-psychopharmacology & biological psychiatry, 26 (3), 457-61 PMID: 11999895

Rosenberg S, Templeton AR, Feigin PD, Lancet D, Beckmann JS, Selig S, Hamer DH, & Skorecki K (2006). The association of DNA sequence variation at the MAOA genetic locus with quantitative behavioural traits in normal males. Human genetics, 120 (4), 447-59 PMID: 16896926

Wang TJ, Huang SY, Lin WW, Lo HY, Wu PL, Wang YS, Wu YS, Ko HC, Shih JC, & Lu RB (2007). Possible interaction between MAOA and DRD2 genes associated with antisocial alcoholism among Han Chinese men in Taiwan. Progress in neuro-psychopharmacology & biological psychiatry, 31 (1), 108-14 PMID: 17007976

Lee SY, Hahn CY, Lee JF, Huang SY, Chen SL, Kuo PH, Lee IH, Yeh TL, Yang YK, Chen SH, Ko HC, & Lu RB (2010). MAOA interacts with the ALDH2 gene in anxiety-depression alcohol dependence. Alcoholism, clinical and experimental research, 34 (7), 1212-8 PMID: 20477771

Patrick-Michael Whittle (2009). Darwinism and the nature of Māori MAI Review

Lea R, & Chambers G (2007). Monoamine oxidase, addiction, and the "warrior" gene hypothesis. The New Zealand medical journal, 120 (1250) PMID: 17339897


Anonymous said...

I have the warrior gene, tested out at Family Tree DNA. I am also female but not typical of females w this gene (i.e. women w warrior gene tend not to be aggressive but happy, surprisingly enough). I always have been extremely aggressive/assertive since I beat the crap out of a kid who was making fun of me in kindergarten. I have been labeled by doctors as way more aggressive than most men, even type A ones, I was type A to the max. Actually some moron doctor said I was the most aggressive than anyone, male or female he ever saw and he wass AFRAID of me, MOOO HAA HAAAAA.

I am 57 years old now, but if someone mess w me, I will knock their a&s out. I have already knocked out guys 6'3" 270 lbs. one good right punch and he was TKO'd laid out on the ground, haha. Still wouldnt mind getting into a decent fistfight but now I live in lala land (Portland, Oregon) and I will go to jail for that, toooooooo bad. Oh BTW, I am descended from a female Viking warrior woman on my maternal line (mtDNA haplotype I1a) and have a lot of Fighting Irish in me (my grandfather was a Diamond Gloves (the name before they changed it to Golden Gloves), another ancestor killed a British (The Enemy if you are Irish) with his bare hands - literally pounded him into the ground. Also, I have ancestors who fought in every US war (except WW2 - nobody was the right age back then) and my great great etc grandfather was a Major in the British Army. I have lived most of my life in New York City, u have to be ready to fight for ur life at any time, at least in my time. Go figure.

Anonymous said...

see at left

Anonymous said...

Correction: my ancestor killed a British soldier (I wrote just British, didnt notice until published) who was actively beating Irish men with the butts of their guns just for being Irish, he will NEVER make a mistake like that again - ;D

Also, I have been tested on the socalled Male/Female brain test. I have taken several, all with the same results - skewed all the way to Male brain at its most extreme. Another go figure.