Genetic Science and Human Milk

Have you ever noticed that the human is the smallest newborn mammal? It turns out that we are born, and we are so immature that we actually need to be breastfed for more time than other mammals, plus we need to have the support of our mother or community to survive. Also, human milk is part of this maturation process, and it is the continuation of the nutrients provision that we used to receive when we were inside the womb. Besides, human milk is considered optimal nutrition for every infant, and it is crucial for this development period. Genetic research and science have provided a better understanding of what can influence human milk production and quality, therefore impacting infants’ health.

Human milk is an everchanging, evolved fluid that is considered an unstructured living tissue, such as blood. In fact, it is capable of transporting nutrients, destroys and confuses pathogens leading them to excretion, and can modulate the epigenetic gene expression. Nevertheless, it is considered to change to fit the infant or infants’ needs, showing specific and modifiable properties depending on its application.

In fact, many factors can contribute to the everchanging capacity of breast milk:

Modifiable factors:

• Special requirements of the infant.
• Mother’s nutritional status.
• Dietary supplementation of Omega-3 fatty acids.
• Duration of the breastfeeding session.
• Infant’s weight.
• Genetic variations.
• Hormonal balance.

Nowadays, technology has offered us the chance to test on a deeper level and recognize genetic alterations that may lead to a lactation problem. Therefore, if we can determine the root cause of this problem, our treatment will be reliable and specific to the mother’s and baby’s needs.

Genetic variations:

• ABCG2 (BCRP)- Riboflavin secretion and milk volume

BCRP/ABCG2 protein is strongly induced in the human mammary gland during pregnancy and lactation. It is ATP-driven and has been associated with breast cancer resistance properties. Nevertheless, most studies on this matter have been performed in mice and cattle, where a mutation of this gene expression resulted in a 63-fold reduction in riboflavin serum concentration and a 3-fold reduction of milk biotin levels. Further, the mice pups fed with this milk only showed a slight reduction of plasma riboflavin 7-12 days after birth.

In women, the ABCG2 c.421C > A polymorphism was shown to affect the export of nifedipine; a calcium channel blocker used to treat hypertension, to the milk. In fact, these findings show that this gene expression alteration not only affects nutrient status but can influence the presence and pharmacokinetics of drugs used during pregnancy.

• ZnT2 (SLC30A2) Mutations and Transient Neonatal Zinc Deficiency (TNZD)

There is a clear link between mutations of the SLC30A2/ZnT2 gene and transient neonatal zinc deficiency. Furthermore, 10 different mutations of this gene have been reported and identified; all of them are linked to zinc-deficient milk production that would eventually lead to a zinc deficiency in infants fed with this breastmilk. Women harboring heterozygous mutations in SLC30A2/ZnT2, which implies that a single gene copy of the wild type (WT) allele is not sufficient for zinc secretion into the milk to meet the infant’s nutritional needs.

• Low milk supply.
• 1 in 576 frequency in the Ashkenazi Jewish population compared to the 1 in 2334 frequency in other ethnic groups.
• Recommended treatment supplementation: 5mg/day continuing with breastfeeding until weaning.

• Genetic Variations in the Sodium Iodide Symporter (NIS/SLC5A5) and Iodine Deficiency in Human Milk

Iodine uptake is crucial for the proper function of thyroid hormones that influence infants’ physical and cognitive development. Furthermore, iodine is one of the nutrients that depends on the mother’s iodine status. Some reports have shown that iodine concentrations in milk are 20 to 50-fold higher than in serum concentrations, which means that iodine maternal reserve could be affected by lactation. (NIS/SLC5A5) is an iodide symporter, highly expressed in the mammary gland during lactation and late pregnancy. Also, a mutation in this gene can lead to ITD (iodide transport defect, which can contribute to developing conditions like congenital goiter and hypothyroidism. Furthermore, in reported cases, the treatment used to aid this condition relied on mother supplementation with 50mg of potassium iodide tablet.

• MTHFD1 and human milk choline concentrations.

Although choline is not a vitamin, it is an essential part of lipid membrane formation and acetylcholine neurotransmitter; choline is essential for rapid growth and infant development. Nevertheless, the importance of MTHFD1 is that it encodes a protein that allows 3 enzymatic actions. This will also provide one-carbon derivates that will serve as substrates for methionine, thymidylate, and de novo purine syntheses. Lastly, the overall effect of a modified SNP in MTHFD1 will lead to an increased choline concentration in human milk.

• Fat percentage in breast milk and DGAT1

Diacylglycerol o-acyltransferase 1 (DGAT1) gene encodes for one of the enzymes that covalently attaches diacylglycerol to long-chain fatty acyl-CoAs to form triglycerides. Furthermore, fat is the major energy source in the infant’s diet. Fat has been largely studied, and it is concluded that it varies greatly depending on the lactation duration and the baby’s needs. Also, any alteration in the DGAT1 code is associated with congenital diarrhea and protein-losing enteropathy in infants. Nevertheless, more studies are needed to elucidate the specific action that this gene has over human health and milk production.

• Fatty acids desaturases (FADS1 and FADS2) and fatty acid composition of human milk

These two enzymes participate in the synthesis of DHA from alfa-linolenic acid. DHA levels in plasma and breast milk of women with FADS1 rs174561, FADS2 rs174575, and intergenic rs3834458 were found in lower proportions. Multiple studies found that the low levels of DHA could not be compensated for by dietary fish consumption.

• Variation of FADS1 rs174556 has an important influence on EPA and ARA levels.
• ELOVL2 and ELOVL5 mutations, along with FADS, can also affect the PUFA composition on human milk. ELOVL codes for elongase enzyme and therefore affects long-chain polyunsaturated fatty acid content on human milk.

Multiple genes have been associated with cow’s milk variations; therefore, studies of these genes should be applied to human milk.

• Lipid metabolism: TRIB3, SAA1, SAA3 and M.SAA3.2.
• Secretory functions in the mammary gland: VEGFA.
• Mammary gland development: PTHLH.

DNA assessment:

DNA assessment can provide a vast array of information. Take a closer look at how a DNA test can be applied to your health.

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As new studies rise up with novel genetic information and assessment tests become available for patients, the nutritional treatment can be personalized to the patient’s needs. Nevertheless, the importance of human milk and breastfeeding its application and benefits are receiving increasing attention, this can provide better knowledge and better treatment plans to breastfeeding mothers and babies.

Breastfeeding is never easy, and even if it is liked to many benefits, for mothers and babies, sometimes is unachievable. Indeed, the feelings that come with not being able to provide the best nutrition to your baby, or having a low milk supply can cause stress and guilt to the mother. Therefore, having the right genetic assessment, and providing the right nutritional supplementation treatment (whenever it is needed) can guarantee better health to the mother and baby, and relieve mom from worries.- Ana Paola Rodríguez Arciniega. Master in Clinical Nutrition

The berry genetic smoothie:

• 1/2 cup blueberries (fresh or frozen, preferably wild)
• 1 medium carrot, roughly chopped
• 1 tablespoon ground flaxseed or chia seed
• 1 tablespoons almonds
• Water (to desired consistency)
• Add a small piece of ginger

Blend all ingredients, best served at the moment.

References

Golan, Yarden, and Yehuda G. Assaraf. “Genetic and Physiological Factors Affecting Human Milk Production and Composition.” Nutrients 12.5 (2020): 1500.

Wambach, Karen, and Becky Spencer. Breastfeeding and human lactation. Jones & Bartlett Learning, 2019.

Andreas, Nicholas J., Beate Kampmann, and Kirsty Mehring Le-Doare. “Human breast milk: A review on its composition and bioactivity.” Early human development 91.11 (2015): 629-635.

Dr. Alex Jimenez’s Blog Post

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