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Genetic Susceptibility

Genetic susceptibility refers to a person’s increased chance of developing a particular disease based on their genetic makeup.Inherited genetic variation has been studied for over 100 years. Geneticists examine how different genes can increase a person’s risk of developing certain diseases. 

Genetic susceptibility studies have been done in two ways with different points of focus. The first, is based on identifying a single gene with different variations. These variations are linked to specific Mendelian patterns that give way to disease inheritance. For example, X-linked, dominant, and recessive genes. The other approach focuses more on examining and understanding how many genes and their connections can increase the likelihood of a person developing a disease. 

Typically, genetically susceptible diseases that are inherited through basic Mendelian patterns, are less common and usually rare. These diseases are usually developed at earlier ages. Some of these diseases are, sickle cell anemia, cystic fibrosis, phenylketonuria, and phenylketonuria. 

Individuals with these genes are also more susceptible as their genes connected to more severe forms of common diseases. For example, mutations in low-density lipoprotein receptors can cause familial hypercholesterolemia. This makes individuals more susceptible to early forms of heart disease.

Genetic Susceptibility and Breast Cancer

Genetic susceptibility also plays an important role in a person’s likelihood of developing breast and ovarian cancer. Some forms of breast cancer that are inherited are another example of Mendelian inheritance. These forms for breast cancer can be linked to mutations in the BRCA1 and BRCA2 genes. These mutations can make a woman more susceptible to early forms of breast cancer and ovarian cancer. 

If a woman is identified with carrying these genes, she is more genetic susceptible and has an increased chance of developing these diseases. Women with these genes are much more likely to develop breast cancer than those without the same genotype. 

These types of genetics diseases commonly exhibit a genetic phenomenon called allelic heterogeneity. This occurs when there are  multiple mutations of the same gene and are associated with the same disease. Allelic heterogeneity is usually specific to a certain population and has been known to represent demographic and mutational history of the population. Individuals belonging to this demographic have a higher level genetic susceptibility and are more likely to develop the disease.

Genetic Susceptibility and Increased Risks

The increased risk of a genetic disease can be associated with locus heterogeneity. This means that any harmful mutations of genes can increase genetic susceptibility and the risk of a person developing a disease. 

Genetic susceptibility is a common issue and can be seen in diseases like Alzheimer’s and polycystic kidney disease. Allelic heterogeneity and locus heterogeneity are both sources of variations in these disease phenotypes. They can have a variety of effects on disease development including initiation, progression and overall severity of the disease.

Environmental Factors and Genetic Susceptibility

In addition to genetic susceptibility, environmental factors also impact the likelihood of a person developing diseases. Etiologic heterogeneity is the combination of environmental and genetic heterogeneity. The phenomenon that occurs when the general population of multiple groups of disease cases demonstrate similar clinical features, despite differing in exposures, is referred to as etiologic heterogeneity. 

By discovering and examining diseases as well as environmental factors and genetic susceptibility, insight into etiology of diseases and identification of causes can be made. Through these studies, results can be examined to identify the potential gene-gene interactions as well as gene-environment connections. This is important in understanding the process of disease development and identification. Disease prevention strategies can be established by identifying etiologic heterogeneity and analysing the molecular epidemiology of diseases. 

Whereas the Mendelian approach is based on genetic susceptibility and singular genes, the other type of study focuses on how variations in genes contribute to variations in disease risks. By examining the connections between multiple genes, a deeper understanding of diseases and genetic susceptibility can be achieved.

This involves examining how genes interact together as well as how environmental factors can impact the development of diseases.This is evident in how the distribution of disease risks are seen within a population. This approach is typically used to examine and understand the genetics of birth defects, risk factors, and more common diseases. There are several steps that must be followed in order to develop this understanding.

Environmental Factors, Genetic Susceptibility, and Familial Aggregation Studies

Familial aggregation refers to the grouping of specific traits, disorders, and behaviors within a given family. Family aggregation can be a result of genetic susceptibility as well as shared environmental factors.

The first step of studying the role of environmental factors, genetic susceptibility, and familial aggregation involves examining participants. These participants are usually asked a variety of questions including a detailed history of their family. This allows the researcher to assess the potential presence of familial aggregation. 

When an individual with the disease being studied has more relatives that are also affected by the same disease than those who aren’t, familial aggregation and genetic susceptibility can be established. Although familial aggregation can also be accounted for with genetic etiology, it can also demonstrate exposure to environmental factors that contribute to the disease. This can include things like exposure to pesticides, diet, or contaminated drinking water. This occurs when multiple family members are exposed to the same environmental factors. 

If there is evidence of familial aggregation, the next step in research studies focus on estimating the heritability or genetic susceptibility of risk factors or and diseases. Heritability is the proportion of variation in the risk of disease based on a certain population that is connected to unmeasured genetic variations. This is usually inferred through familiar patterns of the likelihood of inherited diseases. 

By using this population based measure of genetic influence, researchers can determine whether additional genetic studies are warranted. It also provides investigators with a null hypothesis that genes are not involved in identifying the risk of disease. 

Heritability and Twin Studies

Some of the most common studies regarding genetic susceptibility are based on twin and biological family studies to determine heritability. 

In order to conduct twin studies, sets of identical, or monozygotic, and fraternal, or dizygotic, are both examined. These studies also focus on both genetic and cultural or environmental inheritance of diseases and genes. 

Heritability studies on identical twins are also divided between twins that have been reared together as well as twins who have undergone separate development in order to determine patterns of inheritance, genetic susceptibility, and the role of environmental factors. 

The examination of sources of phenotypic variation with familie studies have also become more detailed and advanced. This has allowed for the incorporation of model parameters to demonstrate additional genetic components and nonadditive genetic components. This also includes the study of gene-environment and gene-gene interactions as well as individual and shared family environments. The impact of these factors has been proven to vary greatly by age and population.

After significant evidence of genetic involvement is identified, the next phase in the investigation is based on identifying the genes and mutations that are responsible. This helps identify which genes and mutations are connected to increased or decreased risk of diseases. This is done by analyzing genetic linkage and genetic association studies. For instance, the examination of birth defects typically involves the search of specific chromosomal issues including translocations, insertions,duplications, and deletions.

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