Introduction:
Some or other kind of health problem due to congenital genetic mutations is present in approximately 65 percent of people. Hereditary genetic disorders are conditions that are passed from generation to generation. Genetic screening determines whether a couple has a high risk of having a baby with a hereditary genetic disorder.
What Is Genetic Screening?
The medical process of testing a person for the existence of any genetic disease is called genetic screening. This voluntary process which is a part of genetic consultation assesses the changes in the following:
a) Chromosomes - Analysis of genetic changes in the whole chromosome or a part of DNA (deoxyribonucleic acid) or the presence of an extra copy of chromosomes.
b) Genes - Analysis of variation in DNA sequences that might increase the risk of developing a genetic disorder. The scope of gene tests varies from detecting changes in a single nucleotide to the entire genome.
c) Proteins - Any abnormality in the amount or activity level of biochemical proteins or enzymes suggests changes to the DNA (deoxyribonucleic acid).
When Is Genetic Screening Recommended?
Although some genetic disorders are not hereditary and thus cannot be identified by screening of parents, genetic screening is particularly recommended when:
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One or both partners have a genetic abnormality.
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Family members with a genetic abnormality.
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Partners who belong to a high-risk group.
What Are the Types of Hereditary Disorders?
There are four different types of inherited genetic disorders:
Single Gene Inheritance - Also called Mendelian or monogenic inheritance. Here the changes occur in the DNA sequence of a single gene. They have different patterns of genetic inheritance: autosomal dominant inheritance in which only one copy of a defective gene (from either parent) is necessary to cause the disorder, autosomal recessive inheritance, in which two copies of a defective gene, that is, one from each parent is necessary to cause the disorder and X-linked inheritance, in which the defective gene is present on the X-chromosome.
Examples of single gene mutations include cystic fibrosis (inherited disease that can cause damage to lungs and digestive tract), alpha and beta thalassemia (inherited blood disorder), sickle cell anemia (an inherited red blood cell disorder), Marfan’s syndrome (disorder that affects the connective tissues), fragile X syndrome (genetic disorder causing learning difficulty), hemochromatosis (condition in which body absorbs more iron), and Huntington's disease (genetic disorder of breakdown of nerve cells).
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Multifactorial Inheritance, Complex or Polygenic Inheritance - This is caused by a combination of mutations in multiple genes and certain environmental factors. Examples include heart disease, obesity, Alzheimer’s disease, diabetes, arthritis, cancer, and high blood pressure.
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Chromosome Abnormalities - Usually occur due to problems with cell division. For example, Down’s syndrome occurs when there are three copies of chromosome number 21, Klinefelter’s syndrome (XXY), and Turner's syndrome (XO).
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Mitochondrial Inheritance - Caused by mutations in the non-nuclear DNA of mitochondria. Since only the egg cells keep their mitochondria during fertilization, mitochondrial DNA is always inherited from the female parent. Examples include Leber's hereditary optic atrophy (eye disease), myoclonic epilepsy with ragged red fibers, lactic acidosis (when lactic acid accumulated in the bloodstream), and stroke-like episodes (a rare form of dementia).
What Is the Correlation Between Genetic Screening and Reproductive Health?
Large-scale research in reproductive health has led to a better understanding of genetic risk factors, which form a vital part of planning and growing a family, increasing the probability of successful pregnancies, and healthy future generations. In today’s era, genetic disorders are prevalent in a broad population rather than a specific ethnic group. Genetic tests may be performed during any stage of the reproductive life cycle, which is as follows:
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Preconception Stage: Expanded carrier screening (ECS) is diversely used to delineate the carrier status information, thereby assessing appropriate reproductive options.
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Preimplantation Genetic Testing (PGT): Provides information regarding embryo prioritization. In recent times, testing of genetic aneuploidy (PGT-A), as well as gene variants (PGT-M), can be done simultaneously.
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Prenatal Genetic Testing: Assesses the health of the fetus. Various chromosome microarray analysis (CMA) tests form an ideal platform for detecting submicroscopic copy number variation (CNV).
How Is Genetic Testing Done?
The test is usually requested by a person’s doctor or genetic counselor. Before the tests, the individual is informed thoroughly about the benefits and limitations, and possible consequences of the test, known as informed consent. The tests are done on samples from hair, skin, amniotic fluid, blood, and other tissues like the inner surface of the cheek (buccal smear). The sample is then sent to a laboratory where depending on the suspected disorder, the technician looks for specific changes in chromosomes, DNA, or proteins. Screening tests for newborns are usually done using a small blood sample from the baby’s feet. The direct-to-consumer testing option is also available for people who do not need to go to a healthcare provider to obtain a test and, therefore, can directly contact the testing company.
What Are the Various Types of Genetic Tests?
Depending on what condition is suspected in a person, the healthcare provider or genetic counselor selects the appropriate test. If a diagnosis is non-conclusive, a test that looks at multiple genes or chromosomes may be used. However, if a specific condition is suspected, a more focused test is usually preferred.
1. Molecular Tests: Assess changes in one or more genes. They determine the order of nucleotides in one's genetic code, known as DNA sequencing. Types of molecular tests are:
- Targeted Single Variant - Identifies a specific variant in one gene known to cause the disorder. Example testing for HBB gene for sickle cell anemia.
- Single Gene Test - Identify mutational changes in one gene. They help rule out a diagnosis when there are multiple variants in the suspected gene.
- Gene Panel - Identify variants in more than one gene. Often useful to delineate a diagnosis when the symptoms fit a wide array of conditions. For example, epilepsy has multiple genetic causes.
- Whole Exome Sequencing - They analyze a significant amount of a person’s DNA to find the genetic variation. Usually done when single gene tests provide inconclusive results.
2. Chromosomal Tests - They analyze whole chromosomes or DNA to identify large-scale changes, like an extra or a missing copy of a chromosome. For example, William’s syndrome is caused by the deletion of a section of chromosome 7.
3. Gene Expression Tests - Identifies which genes are expressed or active in different types of cells. They study the mRNA in cells. Overexpression or underexpression of a certain gene may be responsible for various types of cancer.
4. Biochemical Tests - These tests study the quantity as well as the quality of proteins as well as enzymes that are transcribed and translated by the genes.
Conclusion:
Genetic screening benefits high-risk individuals with prevention, early treatment, or reproductive options. Advancements in the field of genetics have made it possible to detect numerous genetic conditions. A balanced and informed approach to the development of genetic policies and regularisations must be followed to promote greater equality and support vulnerable groups susceptible to various hereditary diseases.
