Infertility and Genes (Part 1)

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Science Behind Infertility

What is infertility? It is the inability to reproduce and it can affect both male and female due to many reasons. Genes can play a role in the infertility of men and women, but what are genes? Genes are part of the chromosomes that determine different characteristics passed on from the two parents, yet genes can still contribute to disease and/or syndromes. When it comes to determining if genes are causative of infertility, scientists must study the disease further into the chromosomes to determine what particular gene. Before we can get into genes, it is important to understand the way fertility works for both sexes. When a male is fertile, they are able to produce a high sperm count making them fertile once they reach puberty and continue to produce them from then on. On the other hand, women are born with a certain amount of eggs that are released once they are around the age of 12 when they start to menstruate. This means that women have a certain amount of eggs that can become fertilize to get pregnant. So, how do both men and women become infertile? Sometimes we only think about environmental factors, yet there is the need to take a deeper look into the genes that are present since birth to understand how they can affect fertility.

Genes are big contributors to infertility and “There are 2 forms of male or female sterility: Primary and secondary.” (1) The primary forms of infertility for both male and female are due to genetics malfunctions in their reproductive system. The secondary form that they mention are syndromes that either sex can be born with such as “X syndrome” (1). Most syndromes are caused due to something going wrong in the chromosomes, causing both sexes to not be able to undergo the correct process of production of gametes. One chromosomal defect that affects male infertility is accidentally getting either XXY or XYY syndromes. Now, if it is a problem with the genes that contribute to the function of the reproductive system, the defective gene can have an effect that may lead to infertility. For women, they may form mutations in the genes that can lead them to develop “primary ovarian insufficiency” (1) which causes the women to be lose function of their ovaries which is key for them to have children. If there is no function, there will be no eggs released or the necessary hormones to get pregnant.

We know that the body makes hormones that help with reproduction such as Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH). Both of these hormones trigger the production of testosterone for males and estrogen for women if the production of these hormones is jeopardized infertility may occur. In this case, the hormone binder of FSH which is FSHR, the gene which makes up the binder is mutated can cause the binder to not bind this hormone. Gene defects that affect the binder affect the “Follicle-stimulating hormone (FSH)” because it “plays a major role in the development of follicles and regulation of steroidogenesis in the ovary, and in spermatogenesis in the testis”. (2) This hormone can contribute to women becoming infertile when their FSHR gene becomes mutated. As for males, their sperm plays an important factor when it comes to being fertile. If their sperm count is low, then there is a possibility of them not having enough sperms that can make it in the women to fertilize the egg. Now, if the male has a good sperm count but their sperms are abnormal such as they are missing their flagella, then they would not be able to fertilize an egg. These sperms would die from the start since they are not able to swim to their target. Some genes that have been determined to affect the way sperms form are “AKAP4, CCDC39, DNAH1, CFAP43, CFAP44, and CFAP69” (3) but in the study scientists also want to prove that the gene “QRICH2 is a functional molecule essential for sperm flagellar development by regulating the genes associated with the accessory structure of sperm flagella” (4). Now, for women, there is the gene BRCA1 that when changed could affect the egg production in a female. Just as in men, if the gametes are jeopardized it would be very hard for them to conceive. With this gene, women would have lower egg reserves this raises the possibility of becoming sterile. All these genes are key players to allowing either sex to reproduce, and most of these genes can be found in the reproductive organs, except for the FSH which is released from the pituitary gland.

Math/Analytical

Understanding that infertility is not one-sided, meaning not only women are prone to being sterile is important. First off, women are the ones that carry the baby so what percentage of them are affected? For women in the United States, the ages of infertility are “15-44” (5) and this age group is at a “12.0%” (5) risk of being sterile. These are women that cannot conceive after six months or one year of trying to get pregnant and have been affected by genes or other factors such as a syndrome named polycystic ovary syndrome (POF) which has been linked to infertility in women. This is an “endocrine condition that affects 5%-10% of women.” (6) and we know this system is in charge of hormone production. When the hormones are not being produced then the luteinizing hormone (LH) and follicle-stimulating hormone (FSH) will not be generated and are essential in the process of reproduction. “About 10 percent of women (6.1 million) in the United States” (7) cannot conceive and this can be an onset of menopause at an early age, usually women do not go through it until they are in the age of 40 years and older. There is a condition caused by genes called premature ovarian failure that leads to women having fewer eggs reserves contributing to early menopause. A condition where “genes have been studied in POF patients, and mutations in FSH, INHA, FOXO3A (forkhead box O3), FOXL2 (forkhead box L2), and BMP15 (bone morphogenetic protein 15) have shown to cause POF” (6). Now, the percentage of women being infertile is partially understood as not only genes are attributes, but other factors as well that are not mentioned in this paper.

When people think of infertility men are not the first thought, but the reality is that they are affected by this disease too. Sex does not matter because chromosomes and genes are present in everyone. “About 9%” (7) of men cannot become fathers and play a contributing factor since the older they get, the production of sperm goes down. So how do genes give rise to this percentage of infertility in men? Spermatogenic failure is one leading cause for men to not have children and the reason is that the sperm is not able to mature. The genes that can be traced to this disease are “RBYMIAI, BPY2, DBX3Y, USP9Y, DAZI, HSFYI, TSPY1 CDY2A, HSFY1 TAF4B, SMYD3, DMRT1 POWIL2” (6). Not just one gene can be defective but many that can bring rise to a man developing spermatogenic failure. Disease like this one is brought on by “Chromosomal aberrations and single gene mutations account for 10%-15% of male infertility.” (6), so it is important to consider genes changing not for the good of the men. A low sperm count is usually the reason men are infertile but spermatogenic failure can be seen as the culprit as well since the sperm is not able to reach maturity. What can be another reason for sterility in men? First of all the structure of sperm consists of the head and the tail, in order for sperm to move, they must have a working tail and “Persistent poor motility is a predictor of failure in fertilization” (8). As mentioned before, there is a large number of genes that affect the sperm in forming a functioning or no tail at all. The sperm has to be able to have this mobility structure in order to reach the egg since the journey is long because it has to go from the cervix, womb, fallopian tubes, and eventually the egg. Having faulty genes that affect this structure leads to men becoming infertile and not be able to reproduce.

Couples that marry began to plan for a baby, thus they must have unprotected sex during the time the women are ovulating. If they try to conceive for 6 months to a year without being successful, then it is important for them to seek medical help. The doctor will then test sperm count, women egg count, and a vast of other exams to conclude whether the couple is capable of conceiving. Unfortunately, “12% to 15% of couples are unable to conceive, and after 2 years, 10% of couples still have not had a live-born baby.” (7). It can be either the men and women that are not able to reproduce, but genes are to be something to consider as causing diseases that make either sex infertile.

References

  1. Yatsenko, A., and Zorilla, Michelle. (2013). The Genetics of Infertility: Current Status of the Field. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3885174/pdf/nihms-532130.pdf
  2. Erdogan Aydos, O., Eryilmaz,O., Ilgaz, N., Karadag, A., Sunguroglu, A., and Taspinar, M. (2015). Impact of follicle-stimulating hormone receptor variants in female infertility. Retrieved from: http://content.ebscohost.com/ContentServer.asp?T=P&P=AN&K=26404793&S=R&D=mdc&EbscoContent=dGJyMMvl7ESep7U4yOvsOLCmr1Gep7VSsqi4SrGWxWXS&ContentCustomer=dGJyMPGut0qwrrdLuePfgeyx44Dt6fIA
  3. Shen, Y., Zhang, F., Li, F., Jiang, X., Yang, Y., Li, X., Xu, W. (2019). Loss-of-function mutations in QRICH2 cause male infertility with multiple morphological abnormalities of the sperm flagella. Nature communications. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6347614/pdf/41467_2018_Article_8182.pdf
  4. Centers for Disease Control and Prevention. (2016). Infertility. National Center for Health Statistics. Retrieved from: https://www.cdc.gov/nchs/fastats/infertility.htm
  5. Suresh, P., Tsutsumi, R., and Venkatesh, T. (2014). New insights into the genetic basis of infertility. Dovepress. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4259396/pdf/tacg-7-235.pdf
  6. Office on Women’s Health. (2019). Infertility. U.S. Department of Health & Human Services. Retrieved from: https://www.womenshealth.gov/a-z-topics/infertility.
  7. NIH. (2018). How common is infertility? Eunice Kennedy Shriver National Institute of Child Health and Human Development. Retrieved from: https://www.nichd.nih.gov/health/topics/infertility/conditioninfo/common
  8. Kumar, N., and Singh, A. (2015). Trends of male factor infertility, and important cause of infertility: A review of literature. Journal of Human Reproductive Sciences. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4691969/?report=reader

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