Genetics

Genetic Counseling

Homapage / Genetic Counseling

How can a genetic counsellor help?/What is the role of a genetic counsellor?

A genetic counsellor provides information and advice about how a genetic disorder is likely to progress, what risks are involved and what tests and treatments are available.

Who can benefit from genetic counselling?

Genetic counselling is strongly advised if you are planning to have a child and one or more of the following apply to you:

  • You carry or have a genetic disorder such as
  1. single gene disorder
  2. chromosomal disorder
  3. multifactorial disorder
  4. mitochondrial disorder

Genetic counselling can be helpful if you are planning to have a child and you already have a child affected by any of the following:

  • a life-threatening genetic disorder requiring HLA compatible stem cell transplantation
  • chromosomal abnormality
  • congenital abnormality
  • mental and/or motor retardation
  • abnormal sexual development

What can I expect to happen at my appointment with a genetic counsellor?

  • Your genetic counsellor will ask you to provide information about your family history.
  • He or she may carry out a physical examination.
  • You may be asked to provide blood samples for chromosomal analysis, DNA analysis or enzyme tests.

Why might tests be needed?

  • Tests may help identify diseases and inheritance patterns.

What happens next?

  • To enable you to make an informed decision, your genetic counsellor will give you information related to the condition, possible risks for future pregnancies and ways of eliminating these risks.

Main Indications
Recurrent Pregnancy Losses

15 to 20 percent of all recognized spontaneous pregnancies result in miscarriage. In fact, the true rate is probably higher, since most early pregnancy losses are mistaken for delayed menstruation.

Several factors may play a role in recurrent pregnancy losses. They may be anatomical, endocrinological, genetical, autoimmunological or environmental. The most common are fetal chromosomal abnormalities. These are responsible for 50 to 60 percent of first trimester pregnancy losses, 20 to 25 percent of second trimester losses and 5 to 10 percent of third trimester losses.

Most abnormalities in the fetus occur de novo (they do not derive from the parents) and do not carry a high risk of repetition. However, some chromosomal structural fetal abnormalities result from parents being carriers of chromosomal rearrangements.

For this reason, chromosomal analysis is advised for couples experiencing pregnancy losses.  If no abnormalities are found after karyotype analysis, other factors are considered.

Advanced Maternal Age

Women of advanced maternal age have a high risk of producing chromosomally abnormal oocytes, and thus offspring with chromosomal abnormalities. The risk of giving birth to a baby with Down Syndrome increases with age. The risk becomes more pronounced after forty. For example, a woman aged forty-four has a forty times greater risk of having a baby with Down Syndrome (link to table in the PGD page showing the effect of advanced maternal age) compared to young women. For this reason, it is advisable for couples where the woman is of advanced maternal age to be counselled about the possible risks and informed about prenatal and pre-implantation genetic diagnosis techniques.

Severe Male Factor Infertility

Male factor infertility is known to be the primary factor in thirty to forty percent of all infertile cases. Underlying factors should be evaluated in the light of a detailed history, physiological examination, and hormonal and serological tests. Since genetic components have been found to be responsible for a significant percentage of cases of male infertility, genetic tests may need to be performed in order to identify the aetiology. Recent advances in molecular genetics help to identify abnormalities related to male infertility.

Most genetic abnormalities related to male infertility impair the mechanism of spermatogenesis (the process of sperm cell formation). Spermatogenesis is controlled by gene groups called AZF regions on chromosome Y. The deletion on those regions is responsible for azoospermia (no sperm in the ejaculate) and may cause  maturation arrest and morphological abnormalities. In addition, abnormalities on other chromosomes  may be responsible for low sperm count in the ejaculate. Methods used to evaluate male factor infertility include Y-chromosome deletion analysis, karyotype analysis and sperm FISH tests.

Repeated Implantation Failures:

Patients with repeated implantation failures experience absence of any clinical pregnancy in spite of good quality embryo transfers in at least 2 or more IVF cycles. The infertility could be due to male factor, female factor, endocrinologic or could be unexplained. Furthermore genetical factors may underly or accompany with other factors which at the end decreases the chances of pregnancy. Comphrehensive chromosomal analysis which screens 24 chromosomes could be used as a tool to identify and select the best quality embryo that have the best implantation potential by excluding chromosomal abnormalities.  

Structural chromosomal abnormalities

There are three main types of chromosomal rearrangement

Balanced translocation carriers may have fertility problems and may experience multiple pregnancy losses due to unbalanced segregation products in their sperms or oocytes. While the frequency of balanced translocations in the newborn population is 0,2%, this rate increases up to 2,5% for couples experiencing repeated implantation failures and 9,2% for couples experiencing recurrent abortions.

Inversions: 

There are two types of inversions

  • Paracentric inversions
  • Pericentric inversions 

Though inversions are very rarely observed, inversion carriers may experience fertility problems.  During the meiosis of gametogenesis, a single crossover event that occurs between the breakpoints produces unbalanced gametes that carry deletions, insertions, and either zero or two centromeres. PGD can be helpful in the identification of unbalanced gametes.

Consanguineous Marriages (Marriages between blood relatives)

Consanguineous marriages are marriages between blood relatives. The closest degree of consanguineous marriage is marriage between cousins. This is termed as 1st degree. In Turkey, twenty to forty percent of marriages are consanguineous, the rate varying between different regions.

Whereas approximately two percent of babies in the general population are born with congenital abnormalities, the risk is doubled in children born to consanguineous marriages. The reason for this, is that couples in consanguineous marriages have a greater risk of carrying the same genetic disease and this increases the risk of recessive disorders appearing in their offspring. For example, although the parents themselves may not have any complaints, as carriers of the same disorder, they  have  a twenty-five per cent risk of transmitting it to their offspring. For this reason they should be closely monitored to exclude any recessive inherited disorders, such as phenylketanuria and beta-thalassemia.

SAYFA BAŞINA DÖN