話說,什麼是表觀遺傳( epigenetics )呢?簡單來說就是在不改變 DNA 序列的情況下,去影響基因表現,就以乳糖酶來說,人類成長到一定階段不再需要製造了,就用某種不改變乳糖酶基因的方法,來關閉乳糖酶基因的作用。這個好處是,由於乳糖酶的基因沒有改變,因此下一代依然保有正常的乳糖酶基因,還是能製造乳糖酶,不然你的孩子就會無法消化母奶了。但隨著子代的年齡增加,同樣關閉乳糖酶表現的戲碼,就會再來一次。
前面提到歐洲、中東與中非地區人們的基因發生突變之後,成人還是能正常分泌乳糖酶爽爽喝牛奶,但這是什麼樣的突變呢?首先要介紹一個新名詞 — 單核苷酸多態性( Single Nucleotide Polymorphism ,簡稱 SNP ),DNA 是由 ATCG 四個核鹼基排列組成, SNP 指的是 DNA 單一個核鹼基改變了,例如本來是 A 被換成 G ,或 C 變成 T ,被替換掉之後基因表現發生了變化。( PS:其實澱粉酶除了拷貝數重複外,也有 SNP 的變異。)
歐洲與非洲人身上的乳糖續存性很可能是一種 SNP 突變造成的結果,變異的位置是 rs4988235 ,鹼基是 C 表示野生型, T 是突變型( Ref. 7 )。研究發現在這些人身上發現帶有突變型是很普遍的情形( Ref. 4 )。 rs4988235 是什麼意思呢? 這是一種用來代表特定 SNP 位置的編碼方式,全名是 Rs Numbers ,簡稱 Rsid 。
邱文寶, & 林慧珍. (2009). 食物與廚藝: 奶, 蛋, 肉, 魚. 臺北: 大家.(原書: McGee, Harold [2004]. On Food And Cooking: The Science and Lore of the Kitchen: Simon & Schuster.)
Blanchard, C. (2017). A history into genetic and epigenetic evolution of food tolerance: how humanity rapidly evolved by drinking milk and eating wheat. Current opinion in allergy and clinical immunology, 17(6), 460-464.
Evershed, R. P., Payne, S., Sherratt, A. G., Copley, M. S., Coolidge, J., Urem-Kotsu, D., … Burton, M. M. (2008). Earliest date for milk use in the Near East and southeastern Europe linked to cattle herding. Nature, 455(7212), 528–531. doi:10.1038/nature07180
Dunne, J., Evershed, R., Salque, M., Cramp, L., Bruni, S., Ryan, K., … Lernia, S. (2012). First dairying in green Saharan Africa in the fifth millennium bc . Nature, 486(7403), 390. doi:10.1038/nature11186
Perry, G. H., Dominy, N. J., Claw, K. G., Lee, A. S., Fiegler, H., Redon, R., … & Carter, N. P. (2007). Diet and the evolution of human amylase gene copy number variation. Nature genetics, 39(10), 1256.
Mantei, N., Villa, M., Enzler, T., Wacker, H., Boll, W., James, P., … & Semenza, G. (1988). Complete primary structure of human and rabbit lactase‐phlorizin hydrolase: implications for biosynthesis, membrane anchoring and evolution of the enzyme. The EMBO journal, 7(9), 2705-2713.
SNPedia – rs4988235
Alharbi, O., & El-Sohemy, A. (2017). Lactose Intolerance (LCT-13910C> T) Genotype Is Associated with Plasma 25-Hydroxyvitamin D Concentrations in Caucasians: A Mendelian Randomization Study, 2. The Journal of nutrition, 147(6), 1063-1069.
Peng, M. S., He, J. D., Zhu, C. L., Wu, S. F., Jin, J. Q., & Zhang, Y. P. (2012). Lactase persistence may have an independent origin in Tibetan populations from Tibet, China. Journal of human genetics, 57(6), 394.
Uptodate: Risk factors, comorbidities, and consequences of insomnia in adults
Uptodate: Evaluation and diagnosis of insomnia in adults
Uptodate: Sleep hygiene basic rules
Uptodate: Sleep duration recommendations by age from the National Sleep Foundation
Uptodate: Overview of the treatment of insomnia in adults
Uptodate: Behavioral and pharmacologic therapies for chronic insomnia in adults
台灣睡眠醫學學會資料
Nomura K, Yamaoka K, Nakao M, Yano E. Impact of insomnia on individual health dissatisfaction in Japan, South Korea, and Taiwan. Sleep. 2005 Oct;28(10):1328-32.
Eurodin仿單
Stilnox仿單
J. Pineal Res. 2011 Volume52, Issue4 May 2012 Pages 365-375