Human Genetics

, Volume 121, Issue 5, pp 631–633

A strong association between human earwax-type and apocrine colostrum secretion from the mammary gland

Authors

    • Department of Obstetrics and Gynaecology Nagasaki University Graduate School of Biomedical Sciences
  • Koh-ichiro Yoshiura
    • Department of Human Genetics Nagasaki University Graduate School of Biomedical Sciences
    • SORSTJapan Science and Technology Agency (JST)
  • Shoko Miura
    • Department of Obstetrics and Gynaecology Nagasaki University Graduate School of Biomedical Sciences
    • SORSTJapan Science and Technology Agency (JST)
  • Takako Shimada
    • Department of Obstetrics and Gynaecology Nagasaki University Graduate School of Biomedical Sciences
  • Kentaro Yamasaki
    • Department of Obstetrics and Gynaecology Nagasaki University Graduate School of Biomedical Sciences
  • Atsushi Yoshida
    • Department of Obstetrics and Gynaecology Nagasaki University Graduate School of Biomedical Sciences
  • Daisuke Nakayama
    • Department of Obstetrics and Gynaecology Nagasaki University Graduate School of Biomedical Sciences
  • Yoshisada Shibata
    • Department of Radiation Epidemiology Nagasaki University Graduate School of Biomedical Sciences
  • Norio Niikawa
    • Department of Human Genetics Nagasaki University Graduate School of Biomedical Sciences
    • SORSTJapan Science and Technology Agency (JST)
  • Hideaki Masuzaki
    • Department of Obstetrics and Gynaecology Nagasaki University Graduate School of Biomedical Sciences
Short Report

DOI: 10.1007/s00439-007-0356-9

Cite this article as:
Miura, K., Yoshiura, K., Miura, S. et al. Hum Genet (2007) 121: 631. doi:10.1007/s00439-007-0356-9

Abstract

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 (< 0.0002), and the measurable colostrum volume in dry-type women was significantly smaller than in wet-type women (P = 0.0341).

Keywords

Human earwax-typeColostrum secretionABCC11Polymorphism

Short reports

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.

To test this hypothesis, we compared the degree of colostrum secretion to earwax types. The colostrum was obtained from 225 Japanese women on the first postpartum day by 10-min milking both their breasts, and its volume was measured by midwives. Genotyping at rs17822931 was performed as described previously (Yoshiura et al. 2006). The midwives were blind to earwax type of any participants, while obstetricians were also blind to any information on the colostrum secretion status prior to genotyping. All study protocols were approved by IRB, and written informed consent was obtained from all participants. Ninety-two women secreted 0.1–20 ml of colostrum, while the remaining 133 women did not give any recognizable amount of colostrum. Neither the frequency of wet-earwax women without secretion nor the time from delivery to milking differed between 108 primipara and 117 multipara women (data not shown). Genotyping at rs17822931 revealed that 155 of the 225 women were AA homozygotes (dry-type) and 70 GA heterozygotes or GG homozygotes (wet-type). Women in the two groups had no significantly different cesarean-section rates: 33.5% (52/155) of dry-type women versus 38.6% (27/70) of wet-type women (= 0.546, Fisher’s exact test). The frequency of dry-type women without colostrum secretion (105/155 or 67.7%) was significantly higher (< 0.0002, Fisher’s exact test) than that of wet-type women without colostrum (28/70 or 40.0%) (Table 1 and Fig. 1). Such a difference was also seen in primipara women without colostrum: 70.5% (55/78) of dry-type women versus 36.7% (11/30) of wet-type women (P = 0.0019, Fisher’s exact test); and within multipara women without colostrum: 64.9% (50/77) of dry-type women versus 42.5% (17/40) of wet-type women (P = 0.0297) (Table 1). Furthermore, the measurable volume of colostrum (average, 1.6 ml) secreted from 50 dry-type women was significantly smaller (P = 0.0341, Savage test) than that (average, 4.0 ml) from 42 wet-type women; the 25th, 50th and 75th percentiles of the volume in the dry-type and wet-type women was (0.2, 1.0 and 2.0 ml) and (0.2, 1.1 and 4.0 ml), respectively (Fig. 1).
Table 1

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

P value

No secretion

Colostrum secreteda

All women

 Dry-type

155

105 (67.7)b

50 (32.3)b

0.000127

 Wet-type

70

28 (40.0)

42 (60.0)

 

 Total

225

133

92

 

Primipara

 Dry-type

78

55 (70.5)b

23 (29.5)b

0.0019

 Wet-type

30

11 (36.7)

19 (63.3)

 

 Total

108

66

42

 

Multipara

 Dry-type

77

50 (64.9)b

27 (35.6)b

0.0297

 Wet-type

40

17 (42.5)

23 (57.5)

 

 Total

117

67

50

 

aSecretion was defined if the volume was more than 0 ml (ranging from 0.1 to 20 ml)

bFisher’s exact test

https://static-content.springer.com/image/art%3A10.1007%2Fs00439-007-0356-9/MediaObjects/439_2007_356_Fig1_HTML.gif
Fig. 1

Distribution of the colostrum secretion volume by earwax type in 70 wet-type women and 155 dry-type women. Asterisk represents the frequency of dry-type women without colostrum (105/155) was significantly higher (< 0.0002) than that of wet-type women without colostrum (28/70). Each interval of the colostrum volume includes the right end but not the left end

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.

Acknowledgments

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.

Copyright information

© Springer-Verlag 2007