Changes in the genes, chromosomes, and protein are identified in a medical test called Genetic testing. This test is performed to know someone’s chances of developing or passing the genetic disorders. This test can either confirm or rule out the suspected genetic condition. This test looks for changes in the following.
1. Genes
Changes in the DNA sequence to identify the mutation in genes are determined by genetic testing. These changes can either cause genetic disorders or increase the risk of such disorders. The gene test analyzes individual DNA building blocks of one or more genes. The gene test can also analyze a person’s genome, meaning all DNA of a person.
2. Chromosomes
The whole chromosome or long length of the DNA is analyzed by this testing which enables us to know large genetic changes. For example, an extra copy of the chromosome. This extra copy of the chromosome can cause a genetic condition.
3. Proteins
This test enables us to study the amount or activity level of protein or enzyme. Any abnormality of these two indicates DNA changes that can cause a genetic disorder.
Types of genetic testing
Changes in the genes, chromosomes, and protein can be analyzed in many tests. While recommending a test for genetic changes, the doctor takes many factors into the consideration before he decides on an appropriate test. These factors include suspected condition(s) and their association with genetic changes. If the diagnosis is not helpful then a special test is used to study many genes or chromosomes at the same time.
Following are some tests used for genetic testing
Molecular tests
This test enables us to know the order of DNA building blocks in someone’s genetic code. This process is called DNA sequencing. The molecular test can determine changes in single or more genes. The molecular tests vary in their scope and are discussed below.
1. Targeted Single variant
This test is performed to look at specific variants in the single gene which can cause a specific disorder. For example, the specific variant in the hemoglobin subunit beta gene can cause a disorder called sickle cell disease. If someone is known to have a particular variant then this test can also be used to know about other family members’ conditions about the same variant.
2. Single gene
Many genetic changes in a single gene can be studied in a single gene test. These tests are done to confirm the specific diagnosis when a suspected condition involves many variants in single gens causing this suspected condition.
3. Gene Panel
These tests are used to determine variants in more than one gene. This test is ordered by the doctors to pinpoint the diagnosis when symptoms of a particular condition are also present in many other conditions. A Gene panel test is also performed when the suspected condition is caused by variants in many genes. For example, epilepsy is characterized by many variants in many genes.
4. Whole-genome sequencing and whole-exome sequencing
These tests are performed to know genetic variations by analyzing the bulk of DNA of an individual. This test is particularly helpful when the single-cell or panel testing fails to complete the diagnosis of a particle condition. This test is also used when the genetic cause is unclear. This test is more expensive but time-saving multiple single genes or panel testing. These technologies are comparatively new and also called next-generation sequencing (NGS). These NGS tests are helpful in the diagnosis of nasopharyngeal carcinoma even in the person who has not developed any symptom.
Nasopharyngeal carcinoma is more common in China than in other parts of the world. That is why diagnosis techniques of this type of cancer are quite advance in china. Take 2 health has commercialized the next generation sequencing (NGS) test in China to diagnose the nasopharyngeal cancer
Chromosomal tests
Large-scale genetic changes can be identified by analyzing whole chromosomes or long lengths of DNA. These changes are given below.
1. Presence of an extra copy of chromosome or a missing chromosome. These are also called Trisomy (extra copy of chromosome) and Monosomy (missing chromosome), respectively
2. A large piece of the chromosome is added or missing. Added means duplicated and missing means deleted.
3. Translocations of the segments of the chromosome. Translocations mean rearrangements. genetic
This type of testing is important because certain conditions are related to specific genetic conditions and the chromosomal test is one of the best ways of detecting suspected conditions. For example, a genetic disorder called William’s Syndrome. This syndrome is caused by the missing part of chromosome 7.
Gene expression tests
The genes can be active or inactive in a different types of cells. The active genes are called ‘On” and inactive “off”. Gene expression tests are performed to know which genes are on or off in different types of cells. When the gene is active, the cell produces mRNA (a molecule called messenger Ribonucleic Acid). The cell produces mRNA by responding to instructions from genes. This mRNA serves as the blueprint to make protein. The gene expression tests are employed to study the mRNA present in the cell to determine which genes are on. Overexpression also called too much activity of the gene can be an indicator of any type of cancer. Similarly, underexpression also called little active genes is also suggestive of many types of cancer.
Biochemical tests
Biochemical tests allow studying the amount or activity level of the proteins or enzymes that are produced by the genes. These tests are an indirect way of analyzing DNA. Abnormalities in the number of activity levels of the protein indicate that some changes in the DNA are present which are responsible for the genetic disorder. For example, biotinidase deficiency is a genetic disorder caused by the deficiency of an enzyme called the biotinidase enzyme. This biotinidase deficiency is caused by a BTD gene variant
In conclusion, genetic disorders can lead to cause many diseases and conditions which are difficult to diagnose. Advancement in genetic testing especially Next Generation Sequencing enabled us to pinpoint the diagnosis of many disorders including cancer and also for differential diagnosis.