Guide
Consanguinity and carrier status
How common marriage between blood relatives is in Türkiye, its link to recessive inheritance, premarital and expanded carrier screening, informing relatives and genetic counseling. Sourced information without blame; the decisions are yours.
How common is consanguineous marriage in Türkiye?
Figures vary by survey, year and definition; that is why we give each figure with its source and year.
National population survey (TNSA 2018)
The Turkey Demographic and Health Survey (TNSA) is carried out by the Hacettepe University Institute of Population Studies. According to 2018 data, 23.8 percent of women aged 15–49 who had ever been married were related to their spouse. 11.0 percent were married to a first cousin. In the first survey in 1968, this rate was 26.9 percent. The figures were taken from an article analyzing these data.
The rate is falling in newer marriages
The same study also grouped women by the years in which they married. Among women who married in 1993 or earlier, consanguineous marriage was 40 percent. Among those who married between 2014–2018, this rate fell to 16 percent. The share of first cousins among consanguineous marriages also fell from 85 percent to 46 percent. So marriage between relatives is still common, but it is becoming less so.
Source: Koç İ. Turk J Public Health 2022 (TNSA-2018, evlilik kuşaklarına göre)
Why do you see different figures?
In a national survey by the Ministry of Health in 2013, consanguineous marriage was found in 18.5 percent of married women. Of these, 57.8 percent were first-cousin marriages. Some sources look only at civil marriages registered in a given year. Some ask all married people. Some count only first cousins. That is why you may see different rates in the news.
Source: Kaplan S ve ark. Türkiye'de akraba evliliği sıklığı, ulusal araştırma, J Biosoc Sci 2016 (PubMed 26892044) · Koç İ. Turk J Public Health 2022
Being related, recessive inheritance and chance
For consanguineous couples, the chance of some diseases can be higher; but it is important to know how large that increase is.
Recessive inheritance in brief
Some diseases appear only if both copies of a gene are changed. This is called recessive inheritance. The mother and father are usually healthy carriers. If both are carriers, in each pregnancy the chance that the child will be affected is 25 percent. The chance that the child will be a carrier is 50 percent. The basics are also in the “Planning a pregnancy” guide.
Source: MedlinePlus Genetics: Kalıtım örüntüleri · MedlinePlus Genetics: Olasılığın her gebelikte aynı olması
Why might relatives carry the same change?
Blood relatives come from shared ancestors. That is why they share some of their genes. According to a review, first cousins share about one eighth of their genes. If there is a change in the family, it is more likely that both partners carry the same change. Experts usually define a relationship of second cousins or closer as “consanguineous marriage.”
Source: Hamamy H. Akraba evlilikleri: birinci basamakta gebelik öncesi danışma, J Community Genet 2012 (PMC3419292) · Bennett RL ve ark. NSGC önerileri, J Genet Couns 2002 (PubMed 26141656)
How much does the chance increase?
According to a review, the chance of a birth defect in first-cousin couples is given as twice that of the general population. In the example, the general chance is 2.5 percent and for cousin couples it is 5 percent. The same review also gives the increase as 1.7 to 2.8 percentage points above the general chance. In a birth study in the UK, cousin marriage also roughly doubled the risk of a birth defect. You can ask about the chance for your own family in genetic counseling.
Source: Hamamy H. J Community Genet 2012 (PMC3419292) · Sheridan E ve ark. Born in Bradford çalışması, Lancet 2013 (PubMed 23830354)
Being related is not the only factor
In the same UK study, the risk was also higher for some mothers older than 34. When the mother had a higher level of education, the risk was lower. So birth defects have many causes. Recessive diseases can also occur in children of partners who are not related. That is because anyone’s family can include carriers.
Source: Sheridan E ve ark. Lancet 2013 (PubMed 23830354) · MedlinePlus Genetics: Kalıtım örüntüleri
Talking with respect, without blame
No one chooses to be a carrier; this section describes non-judgmental language within the family and in health care.
Being a carrier is not a flaw
According to the Ministry of Health’s field guide, most thalassemia carriers do not know it. Most people only find out when a child is born with the disease or through a special blood test. So being a carrier is no one’s fault. Feeling guilty when a disease appears in the family is common. You can talk about these feelings with your genetic counselor.
Source: HSGM, Evlilik Öncesi Hemoglobinopati Tarama Programı Saha Rehberi (2018) · MedlinePlus Genetics: Genetik testin riskleri ve sınırları
Fear of stigma
According to a review, some families feel they have to hide a hereditary disease. The reason is fear of stigma within the family and the community. This silence can also make it harder for relatives to get accurate information. You have the right to expect non-judgmental language from health professionals.
Respect for culture and belief
Marriage between relatives is a long-standing tradition in many societies. One review recommends making counseling easier to access rather than condemning these marriages. An expert group also included respect for cultural and social issues in its recommendations. The European Society of Human Genetics defines the aim of screening as enabling the couple to make their own decision. The decisions belong to the couple.
Source: Hamamy H. J Community Genet 2012 (PMC3419292) · Bennett RL ve ark. NSGC önerileri, 2002 (PubMed 26141656) · Henneman L ve ark. ESHG genişletilmiş taşıyıcılık taraması önerileri, Eur J Hum Genet 2016 (PMC4867464)
Premarital screening: lesser-known details
The programs are described in general in the “Newly diagnosed” and “Planning a pregnancy” guides; here you will find only additional information.
Legal basis
Under the Kalıtsal Hastalıklarla Mücadele Kanunu (Law No. 3960 on Combating Hereditary Diseases), the state works to combat hereditary blood diseases. These include thalassemia and sickle cell anemia. Other hereditary diseases that lead to disability are also covered. This work is carried out as part of preventive health services (Art. 1). The details are set by a Ministry of Health regulation.
Source: 3960 sayılı Kalıtsal Hastalıklarla Mücadele Kanunu, md. 1 (mevzuat.gov.tr)
Being a carrier does not prevent marriage
According to the Ministry of Health’s field guide, both partners being carriers does not prevent marriage. Once both candidates’ results are available, a marriage report can be issued whatever the result. However, the couple is always given counseling. According to the guide, beta thalassemia carrier frequency in Türkiye is 2.1 percent. An informed consent form is also obtained from the couple.
Source: HSGM, Evlilik Öncesi Hemoglobinopati Tarama Programı Saha Rehberi (2018) · HSGM, Hemoglobinopati Kontrol Programı
SMA carrier screening: additional information
According to the Ministry, about 1 in 40 to 60 people is an SMA carrier. The blood sample is taken by the family doctor. You can see your result in e-Nabız (the Ministry of Health’s personal health record system). The test is not repeated for someone who has already had this screening. The Ministry recommends this screening before pregnancy to all couples, whether or not there is an affected child in the family.
If both partners are carriers
According to the Ministry’s pages, these couples are referred for genetic counseling. For SMA, counseling is given by medical genetics specialists. In each pregnancy, the chance that the baby will be affected is 25 percent. Options such as testing during pregnancy and embryo testing in IVF are explained in the “Planning a pregnancy” guide. You decide which path to take.
Source: HSGM, Evlilik Öncesi SMA Taşıyıcı Tarama Programı · HSGM, Hemoglobinopati Kontrol Programı
Expanded carrier screening
The views of two major professional organizations on screening that looks at many recessive diseases with a single test.
What is expanded screening?
This screening uses newer testing methods to look at many genes at once. It can be offered to everyone, regardless of a person’s ancestry. Its aim is to identify in advance couples with a higher chance of having an affected child. The couple can then make decisions knowing their options. The state’s premarital screening, by contrast, looks only at SMA and hereditary blood diseases.
Source: Henneman L ve ark. ESHG önerileri, Eur J Hum Genet 2016 (PMC4867464) · HSGM, Evlilik Öncesi SMA Taşıyıcı Tarama Programı
View of the American College of Medical Genetics and Genomics (ACMG)
In a document published in 2021, ACMG recommends offering a certain level of screening to everyone who is pregnant or planning a pregnancy. This level covers diseases carried by 1 in 200 people or more often. It recommends broader panels in certain situations. One is when the partners are second cousins or more closely related. Another is when there is a reason in the family or personal history.
Source: Gregg AR ve ark. ACMG taşıyıcılık taraması uygulama kaynağı, Genet Med 2021 (PMC8488021)
View of the European Society of Human Genetics (ESHG)
According to ESHG, the aim of screening is for the couple to make an informed decision. Success should not be measured by how much affected births decrease. Screening should preferably be done before pregnancy. This allows more options and more time. Every couple found to be carriers should be offered genetic counseling. Panels should focus mainly on severe diseases that begin in childhood.
Source: Henneman L ve ark. ESHG önerileri, Eur J Hum Genet 2016 (PMC4867464)
Limitations
No screening can find every change. According to ACMG, a negative result does not reduce the chance of being a carrier to zero; it only lowers it. Sometimes the meaning of a change found may be uncertain. Sometimes only one of the partners turns out to be a carrier. SGK does not pay for genetic tests a person has done at their own request; details are in the “Genetic tests” guide.
Source: Gregg AR ve ark. ACMG, Genet Med 2021 (PMC8488021) · Henneman L ve ark. ESHG, Eur J Hum Genet 2016 (PMC4867464)
If there is a diagnosis in the family: informing relatives
If there is a known gene change in the family, relatives can also be tested; this is called cascade testing.
What is cascade testing?
When a genetic disease is found in a family, relatives are informed. Then relatives who wish to can be tested. This is called cascade testing. Testing is first offered to those most likely to carry the change. These are parents, brothers and sisters, and children. Depending on the results, testing moves on to more distant relatives.
Source: CDC: Kaskad test hakkında
How can you tell relatives?
You can talk with relatives face to face. You can also write a letter explaining the situation. You can ask another family member for help. You can also go to a genetic appointment together. A copy of your test report can help your relative get tested more quickly. Your counselor can help you plan what to say.
Source: CDC: Kaskad test hakkında
Privacy and personal choice
In Türkiye, a genetic center cannot share a result with third parties without the person’s explicit consent. This rule is written in the regulation (Art. 22). So it is usually you who informs relatives. Whether or not to be tested is each adult’s own decision. Children are generally not tested for diseases that begin in adulthood.
Source: Tıbbi Laboratuvar Hizmetleri ve İleri Teknoloji Tıbbi Laboratuvar Uygulamaları Hakkında Yönetmelik, RG 24.10.2025 · CDC: Kaskad test hakkında
Genetic counseling for consanguineous couples
Counseling is described in general in the “Newly diagnosed” guide; here you will find points specific to consanguineous couples.
When can you seek counseling?
MedlinePlus lists couples who are blood relatives and are thinking of having children among the reasons for counseling. You can also seek counseling if there is a hereditary disease or birth defect in the family. Several miscarriages or a stillbirth are also a reason. Talking before pregnancy allows more time and more options. You can ask your family doctor for a referral.
Source: MedlinePlus Genetics: Genetik danışmanlık neden yapılır? · Henneman L ve ark. ESHG, Eur J Hum Genet 2016 (PMC4867464)
A family tree is drawn at the appointment
According to a review, a detailed family history is taken at the appointment. A family tree covering four generations is drawn. The specialist also asks about shared ancestry on both the father’s and mother’s sides of each partner. If there is a disease with a known diagnosis in the family, the partners can have carrier testing for that disease. Noting the diseases in your relatives before the appointment will help.
Expert views have changed over time
In 2002, the National Society of Genetic Counselors in the US did not recommend additional screening for consanguineous couples beyond a detailed family history. It recommended offering these couples the screening offered to every couple in their community. In 2021, by contrast, ACMG recommended broader panels for consanguineous couples. You can talk with a medical genetics specialist about which test is right for you. Pregnancy options are in the “Planning a pregnancy” guide.
Source: Bennett RL ve ark. NSGC önerileri, J Genet Couns 2002 (PubMed 26141656) · Gregg AR ve ark. ACMG, Genet Med 2021 (PMC8488021)
Questions to ask your doctor
You can print this list, take it to your appointment and note the answers below each question.
- Based on how closely my partner and I are related, how much does the chance change for our children?
- There is a known disease in our family; are we carriers too, and which test looks for this?
- How can we read the result of our premarital screening in e-Nabız, and what does the result not cover?
- Since we are related, is broader carrier screening right for us, and what are its limits?
- If the result is negative, how much chance remains?
- Which of our relatives would it be useful to inform, and where can we refer them?
- Which specialty should we see for genetic counseling, and how can we get a referral?
- What information about our family history should we gather before the appointment?
- What options do we have when planning a pregnancy, and which ones does SGK cover?
This guide is for information only and does not replace medical or legal advice. If you notice missing or incorrect information, please write to us.