Genetic Counselling Topics

It is known that sperm production is governed by genetic structures in the chromosomes and defects in these regions can lead to problems in stages such as sperm formation, maturation and differentiation.

Genetic diseases may adversely affect sperm formation through different mechanisms. For this reason, genetic examinations such as chromosome analysis etc. should be recommended in couples in whom the cause of infertility cannot be determined by other tests, and the reason for these examinations should be explained.

If a genetic disorder is detected after the examinations, the couple should be informed about this, possible risks should be explained, and detailed explanations should be made regarding the recommended procedures to be performed during pregnancy and pre-pregnancy period.

Although approximately 15-20% of pregnancies are thought to end in miscarriage, it is estimated that this rate is higher because women often fail to recognise early miscarriages or consider them as menstrual bleeding that has slipped for a few days.

Various causes play a role in the occurrence of miscarriages. These are chromosomal, endocrinological, anatomical, autoimmunological and exogenous causes.

Fetal chromosomal abnormalities, one of the most important of these causes, are responsible for 50-60% of miscarriages in the first trimester (first 3 months), 20-25% in the second trimester and 5-10% in the third trimester. These foetal anomalies are usually new events and the risk of recurrence in other pregnancies is very low.

However, in some couples, chromosomal irregularities that may cause miscarriages can be detected even if the mother and father are healthy. For this reason, chromosome analyses should be performed both in the cells of the fetal tissue in the abortion material and in blood samples taken from couples with recurrent miscarriages (2 or more miscarriages). If no chromosomal abnormality is detected in the genetic examination, other factors causing miscarriages should be evaluated by a gynaecologist.

Unlike other materials taken for genetic examination (peripheral blood, cord blood, amniotic fluid and chorionic villus), abortion material shows some differences. The absence of living tissue in the sample may prevent the study from being performed. In addition, contact with the external environment during the collection process may cause the growth of microorganisms in some samples, which does not allow genetic examination to be performed. For these reasons, the study may not be completed.

Consanguineous marriages are marriages between people who are related by blood. According to the degree of kinship, the closest is cousin marriages, which we call 1st degree consanguineous marriages, and these are marriages between aunts, aunts, uncles and uncles. The rate of consanguineous marriage in our country is 21-40% and varies according to regions. This rate is the highest rate of consanguineous marriage in the world except for a few isolated societies.

In general, 2-3 out of every 100 children born in the society (2%) are found to have anomalies due to various reasons. This risk is doubled (4-5%) in consanguineous couples. For this reason, pregnancies in consanguineous couples should be followed up regularly and level 2 ultrasonography should be performed. After birth, screening tests should be performed for common and recessively inherited diseases such as phenylketonuria in the newborn. In addition, these couples should be warned before a second pregnancy and should be advised to wait for 1-2 years, as the first findings in some recessively inherited diseases occur in the growth stages after birth.

Since consanguineous marriage increases the risk of carrying the same mutant gene, it also increases the risk of autosomal recessive diseases, which are particularly rare. If an autosomal recessive inherited disease occurs after consanguineous marriage, the risk of having sick children in new pregnancies is 25% for each pregnancy.

The human body consists of cells and these cells contain structures called nuclei. There are 46 structures called chromosomes in the nucleus and chromosomal diseases are observed in case of their deficiency or excess. There are 46 chromosomes in immature egg cells, similar to body cells.

When a girl is born, she has a certain number of egg cells in her ovaries, although the number varies from person to person. After the age of 12, one of these egg cells matures every month. If this mature egg is fertilised with a sperm, pregnancy occurs. If pregnancy does not occur, the egg degenerates and is discarded. Therefore, unlike the sperm cell, the egg cell is not a continuously new structure.

The important point in the maturation process of egg cells is that the genetic structure of the egg cell, which normally carries 46 chromosomes, is halved as a result of this process, in other words, the number of chromosomes decreases to 23. This cycle continues for many years in women. This process can develop incorrectly at any age for a number of reasons, and then chromosomal diseases such as Down syndrome appear.

One of the most important factors affecting the maturation process of the egg cell is advanced maternal age. Scientific studies have shown that the chance of defects in the maturation mechanism of the egg cell increases significantly in women aged 35 years and older. Accordingly, the incidence of babies with chromosomal abnormalities increases significantly in pregnancies of women with advanced age (>35 years).

As a result, the risk of chromosomal abnormalities increases in the pregnancies of older women and Down syndrome (trisomy 21) is most common. The incidence of Down syndrome, which is normally observed in 1 in 700-800 births (less than 0.1%), increases to 1-4% between 40-45 years of age. Therefore, the risks related to chromosomal diseases should be explained to patients with advanced maternal age before pregnancy and prenatal diagnosis should be recommended.

Environmental factors and chemical substances encountered during pregnancy may cause malformations in the foetus. The effect of a teratogenic agent on pregnancy varies depending on the period of pregnancy, the nature of the agent, the duration and the dose used.

Their effect on the embryo is all or nothing in the first 2 weeks and the embryo is lost or continues to develop completely healthy. The effects of teratogenic agents are observed especially in 3-10 weeks when organogenesis occurs. In the later stages of pregnancy, the fetus is less likely to be affected.

In women who are thought to have been exposed to a teratogen during pregnancy, information should be taken very carefully and genetic counselling should be given to the family.