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FERTILITY GENETICS

The variation in reproductive lifespan and female fertility has implications for health, population size and ageing. Fertility declines well before general signs of menopause and is also adversely affected by common reproductive diseases, including polycystic ovarian syndrome (PCOS) and endometriosis. Substantial genetic variation exists for common traits associated with reproductive lifespan and for common diseases influencing female fertility. The understanding of data from GWAS (genome wide association studies) demonstrates the utility of genetics to explain epidemiological observations, revealing shared biological pathways linking puberty timing, fertility, and reproductive ageing and health outcomes. About 10–15% of human couples are infertile, unable to conceive. In approximately in half of these cases, the underlying cause is related to the male.

Preimplantation Genetic Screening/Diagnosis-

 Preimplantation genetic screening (PGS) and Preimplantation genetic diagnosis (PGD) are screening processes designed to increase the chances of a healthy embryo implantation. PGS screens for extra or missing copies of chromosomes, while PGD looks for single-gene defects that may lead to genetic disorders. Women of all ages are at risk of having chromosomally abnormal embryos — even women less than 30 years of age. Preimplantation genetic screening can also be used to help infertile couples learn the reasoning behind their infertility. Most people don’t know why their embryos either aren’t implanting or are resulting in early losses until after genetic testing. Especially for couples dealing with unexplained infertility, PGS can supply some much-needed answers.

Preimplantation Genetic Screening/Diagnosis involves the following steps;

1.    After 5 days of growth, a few cells are micro surgically removed from the embryo and the embryo is frozen.

2.    The DNA of the biopsied cells is evaluated to determine if the inheritance of a problematic gene is present in each embryo.

3.    One embryo is selected which is free from any genetic problems. This embryo will be placed in the uterus by an IVF procedure and wait for a positive pregnancy begins.

4.    Any additional embryos that are free of genetic problems are kept frozen for possible future use and embryos with problematic genes or chromosomes are destroyed.

PGS is recommended in following cases-

·         Women aged 35 and over.

·         Carriers of sex-linked genetic disorders.

·         Carriers of single gene disorders.

·         Chromosomal disorders.

·         Women with recurrent pregnancy losses.

·         Women with more than one failed fertility treatment.

Advantages-

  • Preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS) can help detect known genetic diseases or chromosomal abnormalities.

  • Identifies abnormal embryos, preventing unhealthy embryos from being transferred to uterus.

  • Reduces multiple pregnancy risk by identifying healthy embryos for implantation.

  • Decreases risk to couples or individuals with serious inherited disorders of having children affected with same problem

Noninvasive Prenatal Testing

At present, there are 2 options to ascertain the chromosome health of a fetus in pregnant women:

    • Non-invasive Method. e.g. Combined test(NIPT).

    • Invasive Method. This is a diagnostic test with 100% detection for the aneuploidies but there is a small risk of miscarriage. e.g. CVS and amniocentesis

NIPT, is a technique which analyses cell-free fetal DNA circulating in maternal blood, for prenatal screening and testing of trisomy 21, trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome); we can also screen for other abnormalities including triploidy and microdeletion.

  DNA from the fetus circulates in maternal blood. Unlike intact fetal cells in maternal blood, which can persist for years after a pregnancy, circulating cell-free fetal DNA (ccffDNA) results from the breakdown of fetal cells (mostly placental) and clears from the maternal system within hours. Fetal DNA detected during a pregnancy, therefore, represents DNA from the current fetus.

The testing is non-invasive, involving a maternal blood draw, so the pregnancy is not put at risk for miscarriage or other adverse outcomes associated with invasive testing procedures.

  • NIPT technologies is useful in singleton pregnancies at high risk for trisomy 21 due to:

    • advanced maternal age

    • an abnormal serum screen

    • personal or family history of aneuploidy

    • abnormal ultrasound

The NIPT test requires taking a small maternal blood sample. cfDNA in the maternal blood is then analysed with our proprietary genetic sequencing technology and bioinformatics pipelines to screen for any chromosomal abnormality in the fetus.

 

 

 

MALE INFERTILITY-

A man’s fertility generally relies on the quantity and quality of his sperm. If the number of sperm a man ejaculates is low or if the sperm are of a poor quality, it will be difficult, and sometimes impossible, for him to cause a pregnancy. Male infertility is diagnosed when, after testing both partners, reproductive problems have been found in the male.

Why test sperm DNA?

Over the last decade, a plethora of studies have confirmed that sperm DNA damage testing has strong associations with every early fertility check point. These include impaired fertilization, slow early embryo development, reduced implantation, miscarriage and, in animal studies, birth defects in the offspring. Childhood cancers have also been associated with oxidative damage to sperm DNA as a consequence of paternal smoking.

 

Sperm DNA testing will provide essential information to couples to select the treatment for their particular needs. These include couples with unexplained infertility, men with normal semen by semen analysis prior to embarking on IVF, couples who have had unsuccessful IVF and couples who have had miscarriages.

 

Y chromosome micro-deletions

Also discovered in recent years is that some men with very severe low sperm counts will be found to have deletions in a certain part of their Y chromosome, known as the DAZ gene. Their karyotype is normal (46 XY) but close inspection of the Y chromosome shows there are sections of the chromosome that are missing. A portion of these men will have no recoverable sperm in the ejaculate or on testicular surgery and donor sperm is the only option. With other deletions in the DAZ gene, there is a small amount of sperm present and conception with IVF-ICSI is possible. In these cases, the male offspring which will always inherit their father’s Y chromosome, will also have this deletion, and will themselves be infertile.

Single Gene mutations

A single gene mutation in the gene for Cystic Fibrosis (CF) is associated with absence of the part of the tube (the “vas deferens”) that leads from the testicle to the urethra in the penis. These men are usually carriers for the CF gene mutation and do not themselves have the disease of Cystic Fibrosis. Sperm can be recovered from the testicles in these men to be used for IVF with ICSI but it is imperative that their wife (or egg provider) be fully tested for CF mutations as well, otherwise there is significant risk of having a child with Cystic Fibrosis.

For men with sperm counts routinely in the less than 5 million total motile sperm range, testing for genetic conditions is warranted so that these men or couples can be made aware of the genetic issues and how these issues might affect their offspring.

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