Our genetic information determines our physical makeup. These genes come from our parents. Every cell in our body has 46 chromosomes. A normal male sperm and female egg have 23 chromosomes. When they are fertilized, they form a new cell with 46 chromosomes. One pair of these chromosomes are sex chromosomes, called X and Y. Although a normal sperm cell contains either X or Y chromosomes, a female egg always carries an X chromosome. So it is the sex chromosome in the sperm cell that determines the sex of the baby. If a sperm with a Y chromosome fertilizes the egg, the baby will be a boy (XY), if a sperm with an X chromosome fertilizes the egg, the baby will be a girl (XX).

Genes are part of DNA and are located in chromosomes. Each chromosome carries many genes. They control our growth and help us to be healthy. Sometimes they can be abnormal or damaged. Then they cannot do their job and cause diseases. Some genetic abnormalities are inherited, others are caused by bad luck. Genes are found in pairs. Half of them come from the mother and the other half from the father. A genetic disorder or disease is a disease caused by a complete or partial difference (variation) or change (mutation) in genes. Although the genetic make-up of humans is still not fully understood, it is now known that almost all diseases have a genetic component. Mutations in some genes can be caused by smoking and environmental factors. Some other genetic diseases are inherited in the family. In general, however, genetic diseases are multifactorial inheritance disorders, in which genetic structure and environmental factors are combined. Genes and genetic disorders can be dominant or recessive. For a recessive gene to occur, both sides (both mother and father) must inherit the gene.

Genetic diseases are classified in many ways. The classification according to their structure is as follows;

Simple gene disorders; they are caused by a mutation in only one gene. This mutation can be found on a single or double chromosome. Sickle cell anemia, cystic fibrosis and Tay-Sachs disease are included in this group. Chromosomal disorders are caused by an excess or deficiency of genes in the chromosome or by structural changes. These problems usually occur during the formation of the egg or sperm. Most babies with chromosomal disorders have physical abnormalities, but some may also have mental problems. In Down syndrome, for example, there is an extra gene on chromosome 21 (but there is no abnormality in this gene on the chromosome). This leads to medical problems such as mental retardation, abnormal facial appearance and heart problems.

Multifactorial inheritance disorders are caused by small changes in genes as well as environmental factors. In fact, it is not known exactly why they occur. Some of these disorders can be detected during pregnancy. Sometimes surgical correction is also possible. These include abdominal wall defects, cleft palate, clubfoot and spina bifida. Heart disease and cancer are also examples. Behavior is also influenced by many factors. Both genes and environmental factors influence it. Obesity, alcoholism and some mental illnesses that occur in combination with genetic and behavioral disorders are still under investigation. Classification of genetic diseases according to their inheritance; dominant, recessive or X-linked.

Only one of the parents can inherit a single gene. If one parent has the gene for a dominantly inherited genetic disease, the risk of passing it on to their child is 50% for each child. Examples include Huntington’s disease (an inherited disease of the nervous system that begins at the age of 35-50 and leads to loss of motor control and a decrease in mental functions) and polydactyly, the formation of more fingers on the hand or foot.

Both the mother and the father must carry the gene in order for the child to develop these diseases. If you carry a recessive gene for a disease, this means that you are a carrier. You will not have any symptoms or complaints about the disease. However, you are at risk of passing the disease to your baby. If both mother and father carry the genes for this recessive disease, their baby has a 25% risk of developing the disease. This is why certain diseases are common in certain ethnic groups. Sickle cell anemia, for example.

Diseases caused by genes linked to the X chromosome. These are also called sex-linked diseases. In most X-linked diseases, the abnormal gene is recessive. A woman who carries the X-linked disease gene will not get the disease. This is because normal genes on the other X chromosome are dominant. However, a baby boy who inherits the diseased X chromosome from his mother will develop the disease. This is because there is no other X chromosome with a normal gene to suppress the other one. Color blindness is an X-linked disorder. If you are a carrier of an X-linked disease, your baby boy has a 50% risk of developing the disease. Girls will be carriers at a rate of 50%. Very rarely, there is also a risk that a baby girl will develop the disease. This will only happen if a sick father and a carrier mother have a daughter. If there is a family history of such diseases, it is important to test for carriage. Hemophilia is also an X-linked disease. This is a blood disorder with problems with clotting.

When you start your pregnancy check-ups, it is a good idea to answer the following questions. If your answers are yes, you are at risk of having a baby with a genetic disorder. However, even if this is the case, most couples have a baby without any genetic disorders. Your doctor will help you with genetic counseling and the necessary tests. In addition, even couples who have no family history and no problems themselves can rarely develop genetic disorders in their babies. Therefore, some tests are performed on all women, whether they have a problem or not. First answer the following questions.

– Will you be 35 or older when your baby is born?

– Will the father be 50 or older when your baby is born?

– Do you or your partner or your families have inherited anemias such as Mediterranean anemia?

– Is there a family history of neural tube defects

– Have you or your partner had a baby with neural tube defects?

– Is there anyone in the family with congenital heart disease?

– Is there anyone in the family with Down syndrome

– Have you or your partner ever had a baby with Down syndrome?

– Does anyone in the family have sickle cell anemia?

– Is there a family history of hemophilia

– Do you have a family history of muscle disease?

– Does anyone in the family have cystic fibrosis?

– Is there anyone in the family with mental retardation?

– Is there a family history of genetic diseases, chromosomal disorders or congenital anomalies?

– Do you have a metabolic disease such as type 1 or type 2 diabetes?

– Have you ever experienced miscarriage or stillbirth in previous pregnancies?

Tests on blood and other tissues to detect genetic disorders. There are about 900 tests. Your doctor will order tests according to the risks they find in you. These tests are used to detect genetic disorders in your unborn baby. People who are carriers of a disease are at risk of passing it on to their baby.

This type of testing is also a personal choice. Some people may not want to have these tests, even if there is a high risk. However, it is useful to have it done in case of conditions that can be prevented.

They are performed during pregnancy and can detect certain congenital anomalies. However, these tests only give an indication of the risk, after which other, more detailed and diagnostic tests are necessary. Maternal blood tests are usually performed between 15 and 20 weeks of pregnancy. They can tell the risk of certain conditions such as neural tube defects, abdominal wall defects, Down syndrome and trisomy 18. Sometimes these tests can give a positive result even though the baby is healthy and does not have any disease. The opposite is also possible. In other words, the test may be negative even though the baby has a problem. In addition, most tests are targeted at specific diseases and it is not possible to detect all diseases with these tests.

If an increased risk is detected by screening tests, diagnostic tests are necessary. We can list them as follows; Detailed ultrasonography examination. Ultrasound examination is a test that can be performed at any period of pregnancy. However, detailed ultrasonography performed after the 18th week of pregnancy can provide more information about the health status of the baby. Amniocentesis. This is a procedure in which a small amount of fluid and cells in the sac surrounding the baby are sampled using a needle. The chromosome structure of this fluid and cells is analyzed to see if there are any abnormalities. It is usually performed in the 15-20th week of pregnancy. Chorionic villus sampling. Cells from a small piece of the placenta (the partner) are examined. As in amniocentesis, chromosomal abnormalities are tried to be detected. It can be performed earlier than amniocentesis, at 10-12 weeks. Fetal blood sampling. Also known as cordocentesis, this procedure is used to detect chromosomal abnormalities and other diseases. Here, blood is taken from the vein in the umbilical cord and analyzed. It is usually done if the results of ultrasonography, amniocentesis and chorionic villus sampling are inconclusive. This test can take a week or more to be completed.

The results of all these tests can be explained by a genetic counselor. A genetic counselor is a person with special training in genetic diseases. They help the family to understand the risks and the options available to them. In fact, most babies are born healthy. But some have an increased risk of congenital anomalies. Tests can help identify the risks of these diseases. However, no test is 100% accurate. If you are at risk of a genetic disease, talk to your doctor and get the necessary tests done. Also seek counseling if necessary to make your decision easier.