Ian Sample “One in 500 men carry extra sex chromosome, research suggests” https://www.theguardian.com/society/2022/jun/10/men-extra-sex-chromosome-research-uk-health-issues
ヒトを含む哺乳類の雌はXX、雄はXYという性染色体のペアを通常は持っている。しかしながら、最近英国で行なわれた研究によれば、男性の場合、500人に１人が３つの性染色体を持っている。これはそれまで考えられていた割合の２倍に及ぶ。
Twice as many men carry an extra sex chromosome as previously thought, according to researchers who called for more genetic testing to identify people at greater risk of related medical problems.Research on more than 200,000 men enrolled with the UK Biobank suggests that about one in 500 in the general population has an extra X or Y chromosome, double the number found in earlier work, though only a fraction are likely to be aware of it.
While most men have one X and one Y chromosome, some are born XXY or XYY, putting them at increased risk of health issues ranging from type 2 diabetes, blocked blood vessels and chronic obstructive pulmonary disease (COPD), a lung condition, the study found.
“We were surprised at how common this is,” said Prof Ken Ong, a paediatric endocrinologist at the MRC epidemiology unit at Cambridge and a senior author on the study. “It had been thought to be pretty rare.”
（以前の研究に基づく）XXXの女性；
Working with colleagues at the University of Exeter, the Cambridge team examined DNA from 207,067 men of European ancestry aged from 40 to 70 years old. They identified 231 men with an extra X chromosome and 143 men with an extra Y chromosome. Those enrolled with the UK Biobank tend to be healthier than average, but from the data, the scientists estimate that 1 in 500 men in the general population carry an extra X or Y chromosome.Among the men flagged up in the study, published in Genetics in Medicine, only 23% of those XXY and 0.7% of those XYY had a known diagnosis of an extra chromosome, suggesting there was little awareness of the condition.
Men with an additional X chromosome are often diagnosed when it has an impact on puberty and fertility, though it is also linked to higher body fat, cognitive problems and personality disorders. In the study, XXY men had substantially lower testosterone than XY men, a threefold greater risk of delayed puberty, and a fourfold higher risk of being childless. The effects of an extra Y chromosome are less well understood. XYY men tend to be taller as boys and adults, but appear to have normal reproductive function.
See also
Previous research suggests that about 1 in 1,000 women carry an additional X chromosome, which can lead to similar effects, ranging from faster growth until puberty, delayed language development and reduced IQ compared with their XX peers.
Cambridge University “One in 500 men carry extra sex chromosome, putting them at higher risk of several common diseases” https://www.cam.ac.uk/research/news/one-in-500-men-carry-extra-sex-chromosome-putting-them-at-higher-risk-of-several-common-diseases
XXYの場合は男性性の過少、XYYの場合は男性性の過剰ということになるのだろうか？ それはさておき、ペアという対称性をはみ出してしまう非対称性が問題だということはいえるだろう。性染色体ではないが、染色体の過剰によって惹起される病気として、ダウン症候群*1がある。この病気、昔はMongolismというレイシズム的な呼ばれた方をしていた*2。
*1:See eg. 国立成育医療研究センター「ダウン症（ダウン症候群）」https://www.ncchd.go.jp/hospital/sickness/children/006.html https://ja.wikipedia.org/wiki/%E3%83%80%E3%82%A6%E3%83%B3%E7%97%87%E5%80%99%E7%BE%A4 https://en.wikipedia.org/wiki/Down_syndrome See also https://sumita-m.hatenadiary.com/entry/20080228/1204212786 https://sumita-m.hatenadiary.com/entry/20160808/1470625339 https://sumita-m.hatenadiary.com/entry/20160905/1473088215
*2:ディーヴォの”Mongoloid”の歌詞にも、”One chromosome too many”というフレーズがある。
