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:

Mendelian disorders which are acquired due to mutation in the genes.
Chromosomal disorders which are from the mutation in the chromosome.

Common Genetic Problems Include:

AA amyloidosis.
Adrenoleukodystrophy (ALD).
Ehlers-Danlos syndrome.
Mitochondrial Diseases.
Usher syndrome.

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

Cystic Fibrosis
Thalassemia
Huntington’s Disease
Hemochromatosis
Turner’s Syndrome
Klinefelter's Syndrome
Leber’s Hereditary Optic Atrophy
Cancer
High Blood Pressure
Obesity
Albinism
Apert Syndrome
Down’s Syndrome

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.

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FAQs on Genetic Disorders and Their Inheritance Patterns

1. What are genetic disorders?

Genetic disorders are diseases caused by abnormalities in a person’s DNA or genes. They occur when there is a mutation in a single gene, multiple genes, or whole chromosomes, affecting normal body functions.

Caused by changes in gene sequence or chromosome structure
May be inherited from parents or occur due to new mutations
Examples include cystic fibrosis, sickle cell anemia, and Down syndrome

2. What causes genetic disorders?

Genetic disorders are caused by mutations or alterations in the genetic material of an individual. These changes can disrupt normal protein production and cellular processes.

Single-gene mutations (e.g., sickle cell disease)
Chromosomal abnormalities (e.g., extra chromosome 21 in Down syndrome)
Multifactorial inheritance involving genes and environment
Spontaneous mutations during DNA replication

3. What are the main types of genetic disorders?

The main types of genetic disorders are single-gene, chromosomal, and multifactorial disorders. They differ based on how the genetic change occurs.

Single-gene disorders: Caused by mutation in one gene (e.g., Huntington’s disease)
Chromosomal disorders: Caused by structural or numerical chromosome changes
Multifactorial disorders: Result from multiple genes and environmental factors (e.g., heart disease)
Mitochondrial disorders: Caused by mutations in mitochondrial DNA

4. How are genetic disorders inherited?

Genetic disorders are inherited through specific inheritance patterns such as autosomal dominant, autosomal recessive, X-linked, or mitochondrial inheritance. The pattern depends on the location and type of mutated gene.

Autosomal dominant: One mutated copy causes disease
Autosomal recessive: Two mutated copies required
X-linked inheritance: Mutation on X chromosome
Mitochondrial inheritance: Passed from mother to offspring

5. What is the difference between autosomal dominant and autosomal recessive disorders?

The key difference is that autosomal dominant disorders require only one mutated gene copy, while autosomal recessive disorders require two mutated copies. This affects how the disorder appears in families.

Autosomal dominant: Affected parent can pass it to 50% of offspring
Autosomal recessive: Parents are often carriers without symptoms
Example dominant: Marfan syndrome
Example recessive: cystic fibrosis

6. What are chromosomal disorders?

Chromosomal disorders are genetic conditions caused by changes in the number or structure of chromosomes. These abnormalities affect many genes at once.

Aneuploidy: Extra or missing chromosome (e.g., trisomy 21)
Deletion: Loss of chromosome segment
Duplication: Extra chromosome segment
Translocation: Rearrangement between chromosomes

7. Can genetic disorders be cured?

Most genetic disorders cannot be completely cured, but many can be managed through medical treatment and supportive care. Advances in gene therapy are offering new possibilities.

Symptom management with medications
Surgical correction in some cases
Gene therapy to replace or repair faulty genes
Lifestyle and dietary modifications

8. What is gene mutation in genetic disorders?

A gene mutation is a permanent change in the DNA sequence that can alter the structure or function of a protein. Mutations are the primary cause of many genetic disorders.

Point mutation: Change in a single nucleotide
Insertion or deletion: Addition or loss of DNA bases
Frameshift mutation: Alters reading frame of gene
May be inherited or acquired

9. How are genetic disorders diagnosed?

Genetic disorders are diagnosed using genetic testing, clinical evaluation, and family history analysis. Laboratory techniques identify mutations or chromosomal abnormalities.

DNA sequencing to detect gene mutations
Karyotyping for chromosomal analysis
Prenatal testing such as amniocentesis
Newborn screening programs

10. What are some common examples of genetic disorders?

Common genetic disorders include cystic fibrosis, sickle cell anemia, Down syndrome, and Huntington’s disease. Each results from specific gene or chromosomal abnormalities.

Cystic fibrosis: Mutation in CFTR gene
Sickle cell anemia: Mutation in HBB gene
Down syndrome: Trisomy of chromosome 21
Huntington’s disease: Autosomal dominant mutation in HTT gene