A strong association between human earwax-type and apocrine colostrum secretion from the mammary gland
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- Miura, K., Yoshiura, K., Miura, S. et al. Hum Genet (2007) 121: 631. doi:10.1007/s00439-007-0356-9
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Here we provided the first genetic evidence for an association between the degree of apocrine colostrum secretion and human earwax type. Genotyping at the earwax-type locus, rs17822931 within the ABCC11 gene, revealed that 155 of 225 Japanese women were dry-type and 70 wet-type. Frequency of women without colostrum among dry-type women was significantly higher than that among wet-type women (P < 0.0002), and the measurable colostrum volume in dry-type women was significantly smaller than in wet-type women (P = 0.0341).
KeywordsHuman earwax-typeColostrum secretionABCC11Polymorphism
Human earwax, a secretory product of ceruminous apocrine glands, is a dimorphic trait consisting of wet and dry types. We previously showed that a SNP (c. 538G > A, rs17822931) in the ABCC11 gene is the earwax-type determinant: AA genotype gives dry-type and others wet-type (Yoshiura et al. 2006). As both colostorum and cerumen have a common origin of the secretory glands (Jirka 1968; Petrakis et al. 1975), human earwax type is suggested to be associated with colostrum secretion.
Distribution of dry-type and wet-type women with or without colostrum secreted 24–36 h after delivery
No. of women examined
No. (%) of women with
We have shown that apocrine colostrum secretion from the mammary gland is associated with human earwax-type, leading to an issue that could have very substantial health implications in a wide range of settings from newborn care to cancer etiology. Although several reports suggested a positive association (Petrakis et al. 1975, 1990), our preliminary data denied it (unpublished). Therefore, a role of milk production or lactation initiation in breast cancer remains inconclusive. Endocrine control of lactation develops during pregnancy, and the pituitary gland supplies prolactin and oxytocin as central regulators of apocrine secretion from the mammary gland. Our results suggest that the ABCC11 gene product (MRP8), an amphipathic anion transporter functioning as an efflux pump (Guo et al. 2003), also plays a role in the colostrum secretion as a peripheral factor independent from the endocrine control. Since there has been no evidence that the colostrum from mothers with dry earwax nourishes their infants less, a role of MRP8 in the colostrum may be confined to its volume. Finally, breast feeding or not, and length of time spent feeding might be associated with colostrum secretion. This could have important implications for anticipatory guidance for mothers planning to breastfeed and based simply on their earwax-type.
We thank the volunteer women for their participation in this study, midwives in Nagasaki University Hospital for their assistance to measure the colostrums, and Dr. Joseph Wagstaff for his help and valuable advice. H. M. and N. N. were supported in part by Grants-in-Aid for Scientific Research (Nos. 17591748 and 17019055, respectively) from the Ministry of Education, Sports, Culture, Science and Technology of Japan.