Genetic Birth Defects in Pregnancy

Posted by Chantel Martiromo,  Article By Kyle J. Norton

Birth defects is defined as a condition in which the baby was born with structural or functional abnormalities that can lead to physical or mental disability.
Genetic disease is a inherited disease, passing down from generation to generation, caused by abnormal mutation of a gene or a group of genes or or chromosomal defects, of which can lead to birth defects.

Types of genetic diseases
Genetic diseases can be classified as the below
A. Chromosomal abnormalities
The diseases can be caused by genetic passing through from the parent or an error in cell division. Chromosomal abnormalities can be divided into two basic groups, numerical and structural anomalies.
A.1. Numerical anomalies
Numerical anomalies is a condition of missing either a chromosome from a pair or has more than two chromosomes of a pair. In other words, it has more or fewer chromosomes than the normal number. Types of numerical anomalies include
a. Down syndrome (trisomy 21)
It is a genetic disease caused by the the presence of all or part of an extra 21st chromosome genetic material and most common cause of birth defects in the US, according to the statistic 1 in 800 born with Down syndrome each year. As of today, there are no treatment for children with diseases.

b. Turner syndrome -
Turner syndrome is a type of chromosome abnormalities with the absence of part or all sex chromosomes, leaving a single X chromosome, or 45 total in new born girl. According to the statistic, 1 in 2500 babies in US are born with Tuner syndrome.

A.2. Structural anomalies
It is a result of structural problem of the chromosomes themselves and can be classified as below 1. Deletion mutation
It is a result of missing part of a chromosome or DNA code. many researchers believe that it may be the result of errors in the process of chromosome cross over during the early stage of egg fertilization.
a. Cri du chat
It is due to the deletion of part of the short arm of chromosome 5.
Currently, there is no treatment for the disease.
b. Muscular dystrophy
It is a result of weaken muscles that affect the movement of the new born as a result of the defects of muscles protein that cause the death of the cell and tissue of the muscles. Currently, there is no cure for the disease and most infant born with muscular dystrophy are died at a young age.

2. Inversion
It is a genetic disorder caused by inversion of the part of broken DNA reattachment. If the inversion of the part of DNA is small, it may not cause any problem to the newborns as in most cases, happened to part of the chromosome 9,

3. Translocation
It is a rearrangement of parts between nonhomologous chromosomes.
a. Balanced translocation - the DNA is equally exchanged between chromosomes and none is lost or added. A parent with a balanced translocation is healthy, but he/she may be at risk for passing unbalanced chromosomes in a pregnancy.
b. Robertsonian translocation
It is a case of a centric fusion, as a result of chromosomal rearrangement occurs in the five 13, 14, 15, 21, and 22. chromosome pairs, causing only 45 chromosomes in each of their cells.

4. Rings:
It is a result of a parts of a chromosome has broken off and formed a ring. Many researchers believe that ring chromosome abnormality may be caused by genetic damage of a mutagens. The disease may only cause symptoms if it happens to a region of repetitive DNA sequences at the end of a chromosome,

5. Etc.

B. Single gene defects
It is a result of single gene defect out of 40-60,000 genes presented in the human body leading to the leads to alternation of the DNA code as a result of an defect amino acid sequence in the proteins. Types of Single gene defects include
1. Dominant
As a result of only one abnormal gene from either parent. Researchers found that the risk of the disease increased by a 50% for a baby born with parent with the disorder, including Huntington's disease, Marfan syndrome, etc.

2. Recessive
As a result of both parents are diagnosed with the disease. Bay born with above parent has a 25% inherited the mutation gene, including cystic fibrosis, sickle cell disease, Tay Sachs disease, etc.

C. X-Chromosome abnormality
Women who carry the mutated genes of the X chromosome have 50% risk in giving birth to a X-link related birth defects. Types of disorder is depended to the degrees of expression of the mutation. In X chromosome abnormality, men are affected and women are carriers.
a. Duchenne muscular dystrophy
It is a mutations in the dystrophin gene of the X chromosome that cause rapid muscle desperation.
b. Hemophilia
a bleeding disorder caused by low levels, or absence of, a blood protein. Patients with haemophilia may suffer severe and frequent bleeds, depending to the severity of the disease.

D. Multifactorial problems
It is a type of genes mutation involved many factors, including the environment in the causation of birth defection, including cleft lip or cleft palate, neural tube defects, etc.

E. Teratogenic problems
It is type of mutation gene abnormality caused by exposure to certain chemicals, radiation, alcohol, heavy chemicals, certain medication, etc.

Diagnosis
1. Blood test
a. Maternal Blood Screen
It is a blood test for the levels of proteins, human chorionic gonadotropin (hCG) and pregnancy associated plasma protein A (PAPP-A). If the protein levels are either too high or low, it may be a indication of a chromosomal mutation in the fetus.
b. Maternal Serum Screen
It is a blood test used to identify the risk of birth defect of the fetus at 15 to 20 weeks of pregnancy by screening the trisomy 18 for any abnormality.

2. Ultra sound
Ultrasound allows your doctor to visualize the fetus and around structures and to assess the abnormality the fetus.

3. Chorionic villus sampling
It is a type of of prenatal diagnosis to determine chromosomal or genetic disorders of the fetus with a test of a sample of the placental tissue before 15 weeks. In a sudy of Instruments for chorionic villus sampling for prenatal diagnosis, by Zarko Alfirevic, Peter von Dadelszen, researchers suggested that chorion can be removed through the abdomen or through the cervix using fine needles, plastic or metal tubes or biopsy forceps. The woman's risk of miscarriage increases if several attempts are needed to get chorion, or the gestational sac is damaged. The review found some evidence that small forceps may be more effective and less painful than aspiration cannulae for transcervical CVS. There were no trials found on transabdominal CVS.

4. Amniocentesis (withdrawing a sample of the amniotic fluid).
Amniocentesis is a test of abnormalities of the fetus by withdrawing a sample of amniotic fluid from a woman uterus and examining it in the laboratory.

5. Etc.

Counseling
According to the Centers for Disease Control and Prevention (CDC), approximately 3% of babies born in the United States will have a birth defect. Family who is at higher risk or previous birth defect incidence and have a family history of birth defect, abnormality of the gene is identified in any test or the pregnant mother is over the age 35 are beneficial for birth defect counseling.
According to the American pregnancy association, genetic counseling includes
1. Do you have a history of diabetes, hypertension, cancer, or twins?
2. Are there any diseases that seem to run in your family?
3. Is there a history of genetic disease like cystic fibrosis, hemophilia, or muscular dystrophy?
4. Is there anyone with mental retardation or any kind of birth defect?
5 Have any of your sisters, cousins, or other relatives had problems with their pregnancies?
6. Are your parents alive, and are they healthy?
7. What is your ethnic background?
8. Is there any reason that you suspect that your baby may be born with a birth defect or other medical problem?
The aim of the evaluation is to determine the risk of your baby will get from the disease and provide available options with the family, depending to the data collection, including families risk, interpretation of information, inheritance patterns analysis, risks of recurrence, etc.

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