[Biology Class Notes] on Genetic Disorders Pdf for EXAM

Genetic disorders can also cause rare diseases. This group of cases affects less than 200,000 people in the U.S. According to experts, there may be as many as 7,000 cases. Genes are the basic functional unit of heredity. Genes are composed of DNA that holds the genetic information to instruct the cells to translate different proteins and other hereditary components. DNA or many times RNA is the genetic material in almost all living organisms. RNA is more unstable than DNA which is why DNA is the genetic component in all organisms except some. Sometimes, under some faulty conditions, the genes undergo mutation causing to falter the genetic code. Faulty genes produce faulty proteins that do not work properly. This leads to malfunctioning and genetic disorders.

Some of these genetic disorders are present by birth and some are acquired due to mutations in genes. Hence, genetic disorders are categorized into two categories:

Common Genetic Problems Include:

We will explore more about genetic disorders in this chapter.

Types of Genetic Disorders

1. Mendelian Disorder

Mendelian disorders are either autosomal dominant, autosomal recessive, sex-linked dominant, sex-linked recessive, or mitochondrial and occur due to mutations in a single gene. These disorders can be detected by pedigree analysis. The genetic locus at which the mutation takes place may be a sex chromosome or an autosome and it may be in a recessive or a dominant mode. An autosomal recessive disease is articulated when the mutant gene is present in the homozygous state. In such cases, both the parents are heterozygous, carrying one copy of the mutant gene and one copy of a normal functional gene. In autosomal traits, females and males are equally expected to be affected. Other types of Mendelian disorders are Autosomal dominant, autosomal recessive, sex-linked dominant, sex-linked chromosomal, and mitochondrial.

Examples of Mendelian Disorders are:

• Autosomal Recessive Disorder – Cystic Fibrosis.

• Sex – Linked Disorder- Hemophilia.

• Autosomal Recessive Disorder – Albinism and Sickle Cell Anemia.

2. Chromosomal Disorders

Genetic disorders arising due to mutation in the chromosome are chromosomal disorders. Alteration in the number and functioning of the chromosomes leads to chromosomal disorders. A chromosomal disorder affects many genes at a time and can be fatal. It may occur due to the loss or gain of a whole chromosome.

Examples of Chromosomal Disorders are as Follows:

• Down’s Syndrome which occurs due to the addition of a chromosome on chromosome 21.

• Turner’s syndrome is marked by the absence of an X chromosome.

• Kleinfelter’s syndrome is marked by the addition of an X chromosome, and so on.

3. Multifactorial Genetic Inheritance

Multifactorial inheritance also refers to polygenic inheritance. When many factors occur at the same time leading to genetic anomalies, it is known as multifactorial genetic inheritance. In such cases, environmental factors take place along with gene mutation.

Examples of Multifactorial Diseases are as Follows:

• Heart Disease

• High Blood Pressure

• Alzheimer’s Disease

• Obesity

• Diabetes

• Cancer

• Arthritis

4. Mitochondrial Inheritance

These kinds of genetic disorders arise as a result of mutations in the non-nuclear mitochondrial DNA. Generally, in such cases, each mitochondrion has 5 to 10 pieces of DNA. These anomalies are inherited from the mother. 

Examples of Such Diseases are:

• Leber’s Hereditary Optic Atrophy (LHON).

• Myoclonic epilepsy with ragged red fibers.

• Mitochondrial encephalopathy.

• Lactic acidosis.
  

List of Some Genetic Disorders

Genetic Counselling

Genetic counseling is the process of communication to help individuals or families understand and adapt to the medical implications of genetic disorders. It is the way of detecting if the child before birth will have a genetic disease or can develop any genetic disorder. Counselors in this field can help individuals and their families cope with the effects of a genetic disorder and treat them in some ways.

A few genetic disorders are treated by gene therapy. Research is still underway to know more about genetic diseases and how to treat them. Medical science professionals are trying their best to deal better with such anomalies.

What are the Symptoms of Genetic Disorders?

Symptoms vary depending on the type of disease, affected organs and severity. You may have:

• Behavioural changes or distractions.

• Respiratory problems.

• Mental deficiency, in which the brain is unable to process information as it should.

• Developmental delays involving speech or community skills challenges.

• Eating and digestive problems, such as difficulty swallowing or not being able to process nutrients.

• Orthopaedic organs or face, including missing fingers or lips and a broken lip.

• Movement disorders due to muscle stiffness or weakness.

• Neurological disorders such as fainting or stroke.

• Poor growth or short stature.

• Sight or loss of hearing.

What is the Treatment for Genetic Disorders?

Many genetic disorders have no cure. Some have over-the-counter medications that may slow down the progression of the disease or reduce its effect on your health. The type of treatment that is best for you depends on the type and severity of the disease. With others, we may not get treatment but we can provide health monitoring to try to catch problems early.

You may need:

• Symptomatic medications or chemotherapy to slow the abnormal cell growth.

• Nutrition advice or dietary supplements to help you get the nutrients your body needs.

• Physical, occupational or speech therapy to improve your skills.

• Blood transfusions restore healthy blood cell levels.

• Surgery to repair unusual structures or treat problems.

• Special treatment, such as radiation therapy.

• An organ transplant, a procedure to replace a deformed limb from a healthy donor.

What are the Methods of Identification of Genetic Problems?

If there is a family history, DNA testing of genetic disorders can be an important part of starting a family. Options include:

• Carrier Testing: This blood test shows that you or your partner are experiencing genetic mutations. This is recommended for anyone considering pregnancy, even if you do not have a family history.

• Prenatal Screening: This test usually involves a blood test for a pregnant woman that tells the person how much the fetus is likely to have a normal chromosome.

• Prenatal Diagnostic Tests: You can find out if your unborn baby is at high risk for certain genetic problems. Prenatal testing uses a sample of uterine fluid (amniocentesis).

• Newborn Test: This test uses a sample of your newborn’s blood and is performed on all babies born in Ohio. Early detection of genetic disorders in life can help your child to receive timely care if needed.