Genetic Diseases
Acquiring a disease is a horrifying thought. A lot of people around us are affected by a variety of ailments which vary in severity.
There are many ways one can keep him / her self safe from many diseases; but nothing much can be done about the genetic diseases.
A genetic disease is caused due to abnormalities in genes and anomalies in chromosomes. These abnormalities are especially found in the human genetic material called genome. Let us have a look at the types of genetic disorders.
Types of Genetic Diseases
There are four basic kinds of genetic diseases.
- Single Gene / Monogenic Genetic Diseases
- Multifactorial / Polygenic (Complex) Diseases
- Chromosomal Genetic Diseases
- Mitochondrial Genetic Diseases
Now, we will look into these types of genetic disorders to understand hem more accurately.
1. Monogenic Diseases
These genetic disorders occur due to mutation of a single gene. According to reports, over 6,000 diseases are caused due to a single gene mutation. Genes have certain codes for proteins. When such a part of the gene is mutated which codes for a vital and efficient part of the protein; the protein becomes nonfunctional. Due to this serious condition, severe consequences are faced in form of diseases and ailments.
Studies show that 1 / 200 neonate has to suffer from a monogenic disorder. Some major monogenic disorders include Polycystic Kidney Disease, Marfan Syndrome, Hemophilia and Sickle Cell Anemia. As we know there are dominant and recessive genes, the genetic diseases have some classifications based no this concept. A short account is given below.
- Autosomal Dominant
As the name suggests, it is a dominant gene disorder. For a person to be affected by this kind of genetic diseases, a single mutated copy of gene is enough. Usually, every affected person has one affected parent. A small number of people who inherit this mutation develop the disease. For a child to inherit the mutated gene form parent; chances are 50%. The diseases that fall under this type of disorder include Marfan syndrome, Huntington’s disease, hereditary multiple exostoses, hereditary non polyposis, colorectal cancer and Neurofibromatosis type 1.
- Autosomal Recessive
In this kind of genetic disorders, two mutated copies of gene are required. It isn’t necessary for the parents or one of them to be affected. Usually, both the parents are carriers; that each of them carries a copy of the mutated gene but stays unaffected. Nonetheless, they can easily transmit the mutated gene to their next generation. A carrier couple has 25% chance (in each pregnancy) of giving birth to an affected child. This type includes disorders like Dry Earwax, Sickle cell disease, Roberts syndrome, cystic fibrosis, Niemann-Pick disease, Tay-Sachs disease and Spinal muscular atrophy.
- X-linked Dominant
Males are affected more by this type of disorders. These are caused when the genes on X chromosome is affected. Examples are Rett syndrome etc.
- X-linked Recessive
These are also caused by mutation of gene on X chromosome. Examples are hemophilia A, color blindness, male pattern baldness and Lesch-Nyhan syndrome etc.
- Y-Linked
This type of disorders occurs due to mutation of gene on the Y chromosome. Females are never affected by this disease. Male children inherit the Y chromosome from their fathers only, and females never inherit Y chromosome. This is why only males are affected by these disorders. An affected father will absolutely pass the disease to his every son. Examples include male infertility.
2. Polygenic Disorders
These diseases are more complex than the above mentioned. Contrary to the monogenic disorders, multifactorial or polygenic diseases are caused due to more than one mutated gene. Also, there are environmental factors and lifestyle elements involved in these diseases. These are called complex disorders because it isn’t easy to study and treat them. This is because many responsible factors are still unknown. These disorders mostly run in families like hypertension, diabetes and asthma.
Some of the most widely known disorders include
- Autoimmune disorders (e.g. multiple sclerosis)
- Mood disorder
- Cleft palate
- Diabetes
- Ciliopathies
- Inflammatory Bowel Disease
- Mental retardation
- Refractive error
- Asthma
- Hypertension
Mutated genes are not the only responsible factor for polygenic diseases; instead there are certain environmental conditions as well as lifestyle of a person which contribute to the chances of getting affected by these disorders.
3. Chromosomal Genetic Diseases
A chromosome is a DNA molecule which is made up of genes. Chromosomal genetic diseases occur due to mutation and anomaly in the number or structure of chromosomes. Sometimes, this results in very serious disorders.
Down syndrome is most commonly known chromosomal genetic disorder. In Down syndrome, a third copy of chromosome 21 is created. Turner syndrome is another famous chromosomal disorder.
4. Mitochondrial Genetic Diseases
Egg cells give mitochondria to the embryo for development purpose. This is why; this type of inheritance is called Maternal Inheritance. Leber’s hereditary optic neuropathy is a good example of this kind.
Genetic Diseases Symptoms and Diagnosis
Some of the genetic disorders might be diagnosed at prenatal stages, or immediately after birth. Tests should be conducted in order to know whether or not one’s child is going to be affected with a genetic disorder.
