Genetic counseling
You may be referred for genetic counseling before, during, or during a subsequent pregnancy if it is considered that there is an increased risk of having a child with a disability. It is this question that is considered in this section. Ideally, genetic counseling should be conducted before conception. It's better to take a decision slowly, so that you can collect all the necessary information and get test results.
WHY YOU CAN HAVE TO CONSULT
Genetic counseling goals:
♦ Determine the likelihood that your child will have birth defects or genetic disorders.
♦ Get an explanation of the type of violation and the degree of risk to the child.
♦ Outline possible treatment options.
♦ Identify which prenatal( expensive) tests will determine the disease.
♦ Identify possible routes of action.
♦ Help to make an acceptable decision. Many abnormalities in the fetus can be diagnosed prenatally. However, prenatal tests are performed at will and can be discarded. If the mother undergoes a prenatal test and is told that problems are possible, or if the child is found to have serious abnormalities( during pregnancy or after childbirth), the results can be discussed on genetic counseling with a doctor, midwife or geneticist.
Many people mistakenly believe that all types of congenital abnormalities are more common in children born to older mothers. In fact, most deviations are not related to the age of the mother, and since most children are born in women under the age of 40, they give the greatest number of congenital abnormalities. However, older mothers have a greater risk of having children with Down's syndrome and other chromosomal problems.
Why you can be referred for advice
Couples who have a higher risk of having a child with a hereditary disease or congenital abnormality should be referred for a genetic consultation with
before or early in pregnancy. These people are:
♦ Children with abnormalities If the mother or anyone else in the family has( or lost) a child with disabilities, this should be reported to the doctor. On a consultation, you can find out whether it will affect how likely it is to have another child with the same problems.
♦ Belonging to a particular ethnic group Some genetic disorders are most common in a particular racial or ethnic group. Thus, the Ashkenazi( subethnic group of Jews) have a risk of having an above-average gene for a degenerative neurological disorder called Tay-Sachs disease. Afro-Caribbean residents, in turn, have a high risk of possession of the sickle cell disease gene, and descendants of the representatives of Asia and the Mediterranean-an increased risk of the presence of the thalassemia gene.
♦ If a parent has a deviation gene or an unusual chromosome is found( through testing, ethnic origin, family history, recurrent miscarriages, a general screening program), then the doctor should advise you to undergo a genetic consultation to determine if a non-how serious it is for children and other family members.
♦ Cousins and sister If the prospective parents are cousins on the first line, they will divide their genes in a ratio of 1: 8, if the second line is 1: 32. Thus, there is a risk of an above average of both spouses having the same andthe same damaged gene, so the child has a chance also above the average to have an inherited genetic condition.
However, it is important to remember that in most marriages, normal, healthy children are born between cousins and sisters.
♦ In whom repeated abortions of were registered Mother can be sent for chromosomal testing if she had repeated miscarriages, as the cause may be an unusual chromosome pattern. Usually, testing is not offered until there are two or three lost children, since miscarriage is common and not related to problems in one of the parents.
♦ If the mother believes that shortly before or during pregnancy, she could be exposed to any harmful radiation, for example X-ray, chemical or medicinal effects and it will harm the unborn child, it should be reported immediately to the doctor, as it maygenetic consultation is required.
♦ Who, with prenatal tests, has found potential problems with Genetic consultation can be prescribed if an ultrasound examination or another prenatal test detects a deviation.
What happens during the
consultation A geneticist, nurse or genetic counselor will ask you questions about your relatives to build a family tree, discovering "family disturbances" and determining the likelihood of the child inheriting this condition. For more detailed information, spouses and other family members will be asked to take a blood or saliva test for gene or chromosomal testing.
If it is considered that the child has a high risk of a gene or chromosomal disease, you will be offered amniocentesis, and if the mother is more than 20 weeks pregnant, they may suggest taking a fetal blood test.
Once all the information and test results are known and if the unborn child is diagnosed with an abnormality, you will be informed how this impairment will affect him, what are the treatment methods, and whether abortion is needed.
You will not be told what to do. All tests are performed at will, and you decide how to proceed. A consultant or doctor will tell you about all the pros and cons of each possible option and, at your request, will prepare any other necessary information, but the decision is made only by the mother herself.
How the diseases are inherited
The child receives two genes for each symptom: one from the mother and one from the father. Remember that only one couple can have six boys or six girls in a row, so she can have many children with a problem, the risk is 1: 2 or 1: 4, or the couple can have many healthy children.
New mutations of
Sometimes a child is born with a dominant or X-chromosome-localized disease that neither of the spouses had - the new
. DOMINANT GENES
. Examples of diseases: Huntington's disease, achondroplasia and myotonic dystrophy.
. If a person is the carrier of a dominant gene, thiswill be immediately obvious, unless signs of the disease appear later in life. If there is such a gene, each egg or sperm has a 50:50 probability of producing a defective gene.
Probability of occurrence of a hereditary disease in a child: the probability of each child's disease is 1: 2.
RECEIVING GENES
Examples of diseases: fibrosis, thalassemia and sickle cell disease
A defective recessive gene will not affect the health of the mother and father provided that the paired gene is normal. However, if a child inherits two copies of a defective gene, one from each parent, he will fall ill. If he inherits one copy, he will be a healthy carrier of the disease-like his parent.
Probability of a hereditary disease in a child: , the probability of each child's disease is 1: 4. Unhealthy children are likely to become carriers of the disease in a 2: 3 ratio.
LOCALIZED IN THE X-CHROMOSOME GENES
Examples of diseases: hemophilia, Duchenne muscular dystrophy and color blindness
If a woman is a carrier of a defective gene in the X chromosome, she probably will not manifest the disease, since her other X chromosome, ratherin all, will have a normal version of the gene. A man carrying a defective gene in the X chromosome will suffer from this disease, since he does not have another X chromosome with a normal gene variant.
Probability of a hereditary disease in a child: if the carrier is a mother, the daughter has a chance of becoming a carrier in the ratio 1: 2.Sons have chances to fall ill in the ratio 1: 2. If the father is sick, then all the daughters will be carriers, and the sons will not get sick.
is a mutation. Mutations arise due to errors in copying the gene during the process of producing an egg or sperm. Even if has an child with a new mutation, the following children are not at high risk of developing this disease, but the problem child will pass the gene to their children.
CHROMOSOMAL DISEASES
It is extremely important for a child to inherit the correct number of chromosomes( 46) - the appearance of an additional chromosome means thousands of extra genes;the absence of one - thousands of lost genes.
Trisomy( including Down Syndrome)
If the child inherits an extra copy of the chromosome, he will have three copies instead of two. This condition is called trisomy. Most trisomy lead pregnancy to miscarriage, but some allow the child to grow. The most common is Down syndrome, also called trisomy 21, because the child has three copies of the 21st chromosome. Edwards' syndrome( trisomy 18) and Patau syndrome( trisomy 13) are less common, and are more serious disorders. The risk of a child with Down syndrome increases with the age of a woman: at age 20, it is 1 : 1500, at 30 - 1 : 900 and in 40 - 1: 100.
Additional sex chromosomes
Studies show that at least one in a thousand childrenhas an additional sex chromosome. Such children are usually normal in appearance and behavior, and many live their whole lives without even knowing about the extra chromosome. However, some such children may have problems, for example, men with an additional X chromosome will be infertile. If prenatal tests show that your child has an excess X- or Y-chromosome, then you will be offered a genetic consultation to discuss the consequences.
Translocation
About one person in five hundred has one or more chromosomes, parts of which are replaced by others or broken. Such structural changes are called translocations. A balanced translocation does not cause any problems, since all genes are present, although they are placed differently. If there is an unbalanced translocation( with additional or missing information), miscarriages usually occur, and if the child is born, then he will have the basic physical and mental diseases. People with a balanced translocation have a high risk of producing eggs and spermatozoa with an unbalanced translocation.
MULTIFACTOR
OR POLICY DISTURBANCES OF
Many diseases, for example spina bifida, are usually not the result of a defective gene or chromosome, but result from the combined effects of different genes and the environment. Such diseases are called multifactorial or polygenic. If a child is born with one of such abnormalities, the risk of recurrence in the parents is calculated from the statistical data of observations of other couples who had children with similar diseases.