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15 Most Common Genetic Disorders

Updated on August 12, 2021
Medically Reviewed by
Dr. Dhingra
Written by
Joel
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The human genome is complex, as identified by the Human Genome Project. It contains instructions on a person’s growth and development. The human genome, however, is subject to changes. These changes can affect molecules that make up the DNA or even chromosomes.

What are Genetic Disorders?

Genetic disorders are diseases that are caused by gene mutations, or changes, in a person’s normal DNA sequence. The DNA mutations may be caused by errors in DNA replication or environmental factors. Examples of environmental factors are radiation exposure and cigarette smoking. 

The DNA contains genetic material. It supplies the code for making proteins that allow the body to perform its functions. When a part of the DNA is changed, protein-coding is affected. As a result, the body isn’t able to function as it should. 

The impact of DNA changes depends on where the mutations occurred. Some mutations will have little to no effect. Others will have such a profound effect that they will alter the body’s cell biology. This will cause a genetic disorder.

Categories of Genetic Disorders

Genetic disorders are grouped into three main categories. They are determined by the cause or location of the defect.

Single Gene Disorders 

Single gene disorders are called such because the defects are in one particular gene. Most of the time, inheritance patterns are simple and predictable. These disorders are further classified into three types

  • Autosomal dominant disorders happen when a person has only one altered copy of the applicable gene. The other copy is healthy. An example of an autosomal dominant disorder is Huntington's Disease.
  • Autosomal recessive disorders occur when a person has two altered versions of the applicable gene. An example of an autosomal recessive disorder is cystic fibrosis.
  • X-linked disorders occur when a defective gene is present on the X chromosome. These disorders are often found in males since they possess only one X chromosome. An example of an x-linked disorder is muscular dystrophy.

Chromosomal Abnormalities

Chromosome disorders are also called chromosomal abnormalities. They are genetic diseases that result from changes in the structure or number of chromosomes. Down’s syndrome, or Down syndrome, is a chromosome disorder.

Multifactorial Disorders 

These are also known as complex disorders or multifactorial inheritance. Multifactorial disorders are caused by changes that occur in multiple genes. Often, these are a result of a complex interaction between lifestyle and environmental factors. Cancer is a multifactorial disorder.

How are Genetic Disorders Diagnosed?

A genetic diagnosis is based on several approaches. They are as follows:

Physical Examination

During a physical examination, a geneticist will conduct a thorough exam. It may involve measuring distances between eyes, length of limbs, and head circumference. This is because some genetic disorders have distinct physical characteristics associated with them. Sometimes, facial features can suggest the presence of a genetic condition. 

Additionally, eye exams and neurological exams are also performed. Imaging studies such as magnetic resonance imaging (MRI), computerized tomography (CT) scans, and x-rays may be used to get a picture of the structures found inside the body.

Medical History

A person’s medical history provides valuable insights into a person’s overall health and well-being. This requires a meticulous history-taking process, with information going back as far as birth. 

It is important to include past (and present) health issues, medications, and allergies. Information on past surgeries and hospitalizations is also needed. If the individual has undergone genetic testing, the results should be divulged.

Family Health History

Genetic conditions are often passed down from generation to generation. Information regarding the state of health of family members is very important. This is an essential tool in diagnosing conditions caused by mutations in the DNA.

Parents, siblings, children, and other relatives will be asked about their health conditions. This is usually done either by a genetic counselor or a doctor. Information obtained usually holds valuable clues. It may reveal the inheritance pattern of a certain genetic disorder that runs in the family.

Laboratory Testing

Laboratory tests, such as genetic testing, are used to diagnose genetic disorders.

In the diagnosis of a genetic disorder, there are several types of genetic tests used. These include:

  • Cytogenetic testing
  • Biochemical testing
  • Molecular testing

Cytogenetic tests are used to detect structural abnormalities in chromosomes. Biochemical testing tests for protein function. On the other hand, molecular testing detects abnormalities in DNA sequencing.

Many genetic conditions can now be tested using a screening test and genetic testing. For some conditions without a genetic test, it may be because the genetic cause of such a condition is yet unknown. Or, it may be because a test has not been developed yet. 

In cases such as these, it may help to sequence the entire genome. This could help locate the genetic variant responsible for the condition.

When are genetic disorders diagnosed?

A genetic disorder may be diagnosed during a person’s lifetime. From birth to old age, a diagnosis of a genetic disorder may be made. This is because some features of the genetic condition appear very early or too late. The availability of testing may also affect diagnosis.

A diagnosis is very important, even if there’s currently no treatment available. This can help manage expectations and identify advocacy resources and useful support. 

Common Genetic Disorders

There are more than 6,000 genetic disorders, and most of these are seriously debilitating. Some cause birth defects, and some are even fatal.

Below are some of the most common genetic disorders. It includes their mode of inheritance and the clinical features they present.

Achondroplasia

  • Mode of Inheritance: Autosomal dominant
  • Clinical Features: The affected person will have short limbs relative to the trunk. They will also have a low nasal root, prominent forehead, and redundant skin folds on legs and arms.

Cystic Fibrosis

  • Mode of Inheritance: Autosomal recessive
  • Clinical Features: The patient will have pancreatic insufficiency because of fibrotic lesions. Thick mucus obstructing the lungs and presence of lung infections are also present.

Cri-du-chat Syndrome

  • Mode of Inheritance: Chromosomal abnormality
  • Clinical Features: A high-pitched cry resembling that of a cat is the most common sign. The person will have a small skull, downward slanting eyes, and abnormally shaped ears. Intellectual impairment and delayed motor development are obvious.

Down Syndrome

  • Mode of Inheritance: Chromosome abnormality
  • Clinical Features: Slanted eyes, shortened hands, stunted growth, abnormal teeth, and mental impairment are present.

Duchenne Muscular Dystrophy

  • Mode of Inheritance: X-linked recessive
  • Clinical Features: Skeletal muscle gradually degenerates with impaired respiratory and heart muscles.

Glucose-6 Phosphate Dehydrogenase (G6PD)

  • Mode of Inheritance: X-linked recessive
  • Clinical Features: Anemia because of increased hemolysis is seen.

Hemochromatosis

  • Mode of Inheritance: Autosomal recessive
  • Clinical Features: The patient will exhibit arthritis and enhanced absorption of dietary iron. Cardiomyopathy, cirrhosis, diabetes, and skin pigmentation are also seen.

Huntington’s Disease

  • Mode of Inheritance: Autosomal dominant
  • Clinical Features: There is progressive cognitive, motor, and psychiatric abnormalities. Non-repetitive jerks (chorea) are observed.

Marfan's Syndrome

  • Mode of Inheritance: Autosomal dominant
  • Clinical Features: There is disproportionate height and scoliosis. Heart and pulmonary problems develop. There is also excessive skin elasticity and hypermobility of joints.

Myotonic Dystrophy

  • Mode of Inheritance: Autosomal dominant
  • Clinical Features: Muscle weakness, cardiac arrhythmias, and testicular atrophy in males are present. Cataracts may also develop. An open triangle-shaped mouth is seen in children with congenital form.

Osteogenesis Imperfecta

  • Mode of Inheritance: Autosomal dominant
  • Clinical Features: Deformed and demineralized bones are seen in this disease.

Phenylketonuria

  • Mode of Inheritance: Autosomal recessive
  • Clinical Features: Mental retardation

Polycystic Kidney Disease

  • Mode of Inheritance: Autosomal dominant
  • Clinical Features: Renal cysts, blood in the urine, and kidney failure

Tay-Sachs Disease

  • Mode of Inheritance: Autosomal recessive
  • Clinical Features: There is spasticity, hypotonia, and seizures. A cherry-red spot on the retina is usually the first sign. Blindness may occur. The patient may die at 2 years old.

Turner Syndrome

  • Mode of Inheritance: Paternal error in the transmission of sex chromosome
  • Clinical Features: A patient will have a short stature and webbed neck. They will have a broad chest with widely spaced nipples. There will be sterility and lymphedema. However, they possess normal intelligence.
Dr. Dhingra
Dr. Harshi Dhingra
Medical Reviewer
Dr Harshi Dhingra is a licensed medical doctor with a specialization in Pathology. Dr. Dhingra has of over a decade in diagnostic, clinical, research and teaching work, including managing all sections of Pathology laboratory including histopathology, cytology, hematology and clinical Pathology.
Joel
Content Contributor
Joel is a writer with a passion for the science of DNA and the power of its manipulation.
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