In this case, the risk of blood bond increases, according to the degree of closeness between persons. For example; The risk of having a child with a hereditary disease of a couple who married a 1st-degree cousin. This risk is higher than in the case of a couple who married a 2nd-degree cousin (like a marriage between grandchildren of siblings).
Consanguinity between partners plays a role in the detection of many autosomal recessive inheritance diseases. For this reason, consanguinity couples are required to receive genetic counseling to reduce the risks in terms of hereditary diseases.
Genes provide the transmission of various hereditary features from mother and father to the next generation. In these genes, for any reason, disorders, called mutations that affect human health, can transmit to the next generation.
A Disease will call an Autosomal dominant if it can lead to disease when there is a mutation even in one of two related genes. But it is called Autosomal recessive if it can lead to disease when there are mutations in both related genes. For each human, there is a possibility of carrying mutations that cause recessive diseases without any symptoms of the disease, and it is difficult for these people to be diagnosed unless they have relatives who have this disease. Since consanguineous persons receive their genes from a common ancestor, the probability of carrying a mutation on the same gene is higher than for non-consanguineous persons.
In this way, the risk of emerging of this disease in each child of a couple carrying a mutation in the same gene will be 25%. Unfortunately, many families realize the importance of this situation, only after the birth of a sick child. For this reason, before marriage for couples who want to marry their relatives and before the child is born, the couples should do some geneticist tests.
Some of the hereditary diseases which its emerging risk increases as a result of consanguineous marriages are:
Phenylketonuria: One of the rarely seen hereditary metabolic diseases.For babies who are born in our country, the average frequency of this disease is 1 / 3000-1 / 4000. The most important features of the disease are progressive mental retardation and other nervous system symptoms. Babies with this disease appear completely healthy for 1-2 months after born. Symptoms begin to show after the second month. The development steps lag behind their peers, they can not develop their sitting, speaking, walking skills, they have learning disabilities, problems with behavior.
It is very important to make an early diagnosis and appropriate approach without affecting brain development in this disease. After birth, the disease is screened with heel blood from the baby, the babies diagnosed with this disease should be fed poorly in terms of amino acid of the phenylalanine. If phenylketonuria is detected by neonatal screening and treatment is not initiated in the first 3 months. the mental retardation inevitably develops in line with the severity of the disease.
Cystic fibrosis: The frequency is approximately 1/2500 among live births. The main cause of the disease is the functional disorders of chlorine channels in the skin and various internal organs because of the mutation. As a result of this, problems such as frequently recurrent lung infections, retarded development, chronic and persistent sinusitis, pancreatitis, bowel function disorder in the neonatal period as well as diabetes, liver diseases, infertility in male individuals in later ages arise. The diagnosis of the disease is carried out by biochemical and genetic tests as well as clinical symptoms. The treatment of the disease lasts for lifelong, there is the only supportive treatment for the systems affected by the disease, there is no definitive treatment for the disease.
Familial Mediterranean Fever (FMF): It is a hereditary disease and in some cases, symptoms of this disease are recurrent fever, abdominal pain, recurrent chest, and joint pain.
As a result of recurrent painful attacks, it accumulates in the body a protein called amyloid. Over the years, accumulation, especially in the kidneys, can lead to kidney functional disorder and kidney failure. A medicine called colchicine is used in the treatment of the disease. This medical treatment does not completely remove the disease, but it reduces the frequency and severity of attacks, it prevents the loss of kidney function. The medicine needs to be taken for lifelong.
Thalassemia: It is also known as Mediterranean anemia and it is a type of anemia that is more common in Mediterranean countries. According to the loss of function in the beta globin (haemoglobin beta) genes, thalassemia classified clinically as major and minor. If there is an impairment in a single allele in the individual, it will call the thalassemia minor (thalassemia carrier), and if both alleles are impaired, it will call thalassemia major (Mediterranean anemia). Thalassemia major beginseven before birth. Anemia at a significant level, shape changes in the facial bones due to anemia, and heart failure in the later stages are observed. The patient's need for a lifetime repeated blood transfusions. Thalassemia minor is less dangerous than thalassemia major and requires fewer blood transfusions. As a result of repeated blood transfusions, iron deposits can be seen in various organs in the body and the disease must treat accordingly.
5. Recessive Inherited metabolic diseases are diseases that affect various systems as a result of mutations in both alleles of related genes or as a result of a deficiency or absence of a specific protein or enzyme.
There are many metabolic diseases. The characteristic feature of these diseases includes developmental and mental retardation, internal organ diseases, musculoskeletal disorders, phenotypic changes, visual or hearing problems. These diseases have no definitive treatment. For some diseases, treatments such as substituting the missing enzyme have been tried.
Early diagnosis of these diseases is so much important since only supportive treatment can be given to genetic diseases that occur after consanguineous marriage. For this purpose, prenatal diagnostic methods should be applied during pregnancy or, most importantly, by applying pre-implantation genetic diagnosis, transfer of embryos that do not carry disease to the mother.