Frequently Asked Questions

Genetic disorders can be grouped under four main headings: chromosomal disorders, single-gene disorders, multifactorial disorders and mitochondrial disorders. Chromosomal disorders occur when the number of the structures called chromosomes, normally 23 pairs (46), is lower or higher than normal, or when part of a chromosome is missing or duplicated. Single-gene disorders, of which there are around 10,000, arise from changes, called mutations in medicine, in the genetic units called genes that are located on the chromosomes. This group also includes multifactorial disorders, caused by the interaction of genetic and environmental factors, and disorders caused by genetic changes in the mitochondria, the energy source of the cell located outside the nucleus.

We perform these tests in babies, children and adults at genetic risk, in high-risk pregnancies and in some couples who will undergo assisted reproductive techniques.
Situations in which genetic testing is recommended
- A physical abnormality detected after birth
- Developmental delay and short stature
- Disorders of sex development
- Intellectual disability
- Recurrent pregnancy loss
- Infertility
- Advanced maternal age (35 years or older)
- A high-risk result in the triple test
- A history of a child with a chromosomal anomaly
- A history of a child with multiple anomalies
- An anomaly detected in the baby on ultrasound during pregnancy
- One of the partners carrying a numerical or structural chromosomal abnormality
- Sex-linked inherited disorders (if the disorder could not be identified by other methods)

- After birth: in babies, children and adults
- During pregnancy
- In the preimplantation period (before pregnancy)

Today some genetic disorders can be identified in the 3rd to 4th month of pregnancy with prenatal diagnostic methods (CVS, amniocentesis and cordocentesis), and the pregnancy is terminated if a serious abnormality is found in the baby. Recent advances in genetics make it possible to examine embryos produced by IVF. This procedure, called preimplantation genetic testing (PGT), is performed by taking 1 or 2 cells from embryos that develop after eggs and sperm are fertilized in the laboratory. Special methods are applied to these cells, and numerical and structural chromosomal abnormalities as well as single-gene disorders (such as thalassemia, sickle cell anemia and cystic fibrosis) can be diagnosed in the future baby.

– A numerical or structural chromosomal abnormality detected in the mother or father
– A single-gene disorder in the mother or father, or both parents being carriers of the same single-gene disorder
– Increasing the chance of success in couples undergoing assisted reproductive techniques
– Women aged 37 and over
– Couples with recurrent pregnancy loss
– Couples with severe male infertility
– Recurrent implantation failure

• The primary aim of preimplantation genetic testing is to identify, before pregnancy (at the embryo stage), genetic disorders that are commonly seen during and after pregnancy.
• It is also used to identify genetic disorders that may occur in embryos of couples who will undergo assisted reproductive techniques because of infertility.

• It helps families have healthy children.
• It spares families the medical and psychological trauma of terminating a pregnancy.
• Compared with the lifelong health problems of affected individuals, the difficulties of treatment and the high cost of treatment, diagnosis before pregnancy is a far more beneficial and less costly method.

• Chromosome analysis
• Fluorescence In Situ Hybridization (FISH)
• Polymerase Chain Reaction (PCR)

Genetic counselling means informing people who have or are at risk of carrying a hereditary disorder, and their relatives, about the course of the disorder, treatment options, recurrence risks and possible solutions. The primary duty of the genetic counsellor is to give the family accurate and complete information on the subject being discussed and to present the options. For this reason genetic counselling should never be directive. On the contrary, all information should be explained in a way the person or persons can understand, and the decision should be made by those concerned.
Situations in which genetic counselling is recommended:

• A genetic or hereditary disorder, or being a carrier of one
• Having a child or children with a genetic disorder
• A physical abnormality detected after birth
• Developmental delay and short stature
• Anomalies of sex development
• Intellectual disability
• Recurrent pregnancy loss
• Exposure to a teratogenic agent
• Advanced maternal age (35 or older)
• Consanguineous marriage
• Infertility
• A problem detected in the baby during pregnancy

Consanguineous marriages are marriages between people who are blood relatives. In Turkey the average rate of consanguineous marriage is 21%, one of the highest rates in the world apart from a few isolated communities. In general, anomalies from various causes are found in 2 to 3 of every 100 children born (2%). In consanguineous couples this risk doubles (4 to 5%). If an autosomal recessive disorder appears after a consanguineous marriage, the risk of an affected child in each new pregnancy of the couple is 25%. Pregnancies of consanguineous couples should be followed regularly, and a level 2 ultrasound should always be performed. After birth, the newborn should be screened for common disorders such as phenylketonuria. Because in some genetic disorders the symptoms appear in later stages of development, couples should be advised before a second pregnancy and encouraged to wait 1 to 2 years.

In women of advanced maternal age (35 or older), the risk of chromosomal disorders in pregnancy increases, Down syndrome being the most common. Normally seen in about one in 700 to 800 births, the likelihood of a child with Down syndrome increases with age and ranges from 1% to 4% between the ages of 40 and 45. For this reason, women of advanced maternal age should be informed about the risks before pregnancy, and genetic diagnosis should be recommended during pregnancy.

Various causes play a role in miscarriage. One of the most important, chromosomal anomalies of the baby, accounts for 50 to 60% of first-trimester miscarriages, 20 to 25% of second-trimester miscarriages and 5 to 10% of third-trimester losses. These anomalies are usually new events, and the risk of recurrence in other pregnancies is very low. However, in some couples chromosomal irregularities that can cause miscarriage may be found even though both parents are healthy. Chromosome analysis should therefore be performed both on fetal cells in the pregnancy loss material and on blood samples from couples with recurrent miscarriages. If no cause is found, other factors that cause miscarriage should be evaluated by an obstetrician.

Today reduced fertility is found in about 15% of couples. In most of these cases the cause is male infertility, and genetic disorders are known to affect sperm production negatively through different mechanisms. Therefore the necessary genetic tests should be recommended to couples whose cause of infertility could not be found with other tests, and the reason for the tests should be explained. If a genetic abnormality is found, the couple should be informed, the possible risks explained, and detailed information given about the procedures recommended before and during pregnancy.

• In male infertility the cause is often obstructive azoospermia characterized by congenital absence of the vas deferens due to Y chromosome microdeletions and cystic fibrosis transmembrane conductance regulator (CFTR) gene mutations.
• In addition, numerical anomalies of the sex chromosomes and structural chromosomal abnormalities cause problems in spermatogenesis and therefore in fertilization.
• Mutations of the KAL (X-linked Kallmann syndrome), DAX1 (X-linked congenital adrenal hypoplasia), GNRHR (impaired GnRH secretion) and PC1 (prohormone convertase-1) genes that cause hypogonadotropic hypogonadism, and androgen receptor gene mutations, may be seen together with spermatogenic failure.
• Also, in couples described as secondarily infertile, recurrent pregnancy loss and stillbirths may be seen because of certain genetic abnormalities they carry.

Because there are so many genetic disorders, and especially because each single-gene disorder needs its own test, it is impossible to perform every test in one center. Even today, testing is not possible for many disorders because their genetic cause has not been found or defined. However, tests for some disorders with a known genetic cause can be performed in Turkey. People at genetic risk can therefore apply to the genetic diagnosis centers of universities or private hospitals, where the necessary tests can be performed after evaluation by a geneticist. For genetic tests not performed in Turkey, blood samples can be sent, under the guidance of the geneticist, to centers abroad that work on the disorder concerned.

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