5 Genetic Illnesses

What are genetic illnesses?

Genetic illnesses are often called by different names and terms. The most common include: rare disease, genetic disorder, genetic syndrome, genetic condition.

The broad definition of a genetic illness is one that is caused by a genetic or chromosomal change or mutation in the DNA of an affected individual. A gene or chromosome change can trigger any one of a number of unique symptoms, including characteristic facial features and specific medical conditions, that then make up a rare disease. 

Some genetic illnesses are inherited. This means that the gene or chromosomal change which causes them are passed down from one generation to another, typically from parents to their children. There are a number of types of inheritance patterns. Some genetic illnesses are not inherited, and are the result of a de novo or new mutation. This gene change is usually spontaneous. 

5 genetic illnesses

Apert syndrome

This rare disease or genetic illness has an estimated prevalence of around 1 in every 60-80,000 live births. This prevalence makes it a rare disease. In the US, a rare disease is described as one that affects less than 200,000 people nationally. Apert is known as a multi-system syndrome, meaning its symptoms affect multiple parts and systems of the body. However one of the main symptoms of this genetic illness affects the development of the skull. People with this syndrome often experience a premature fusing of the skull bones which can dramatically change the structure and shape of their skull. 

The genetic cause of Apert is still unknown. Research suggests that mutations in the FGFR2 gene may have a part to play in causing the syndrome but this is yet to be confirmed with any certainty. This is not unusual for a genetic illness to have an unidentified genetic cause. Apert is an inheritable condition, and patients with the syndrome have a 50% chance of their children inheriting the same illness. 

Angelman syndrome

This genetic illness or syndrome is believed to affect around half a million individuals around the world. One of the first main signs of the syndrome is developmental delay in an infant, specially with their crawling and walking skills. This rare disease also presents with other serious medical conditions, including seizures, sleep issues, speech delay and intellectual disability. 

Angelman is not inherited and is usually the result of a spontaneous gene change. There are currently 3 genes identified with Angelman – GABRB3, 15q12 UBE3A, 15q11.2, CDKL5, Xp22.13 

The syndrome is caused by a deletion of several genes on a chromosome. The syndrome is also a result of a chromosomal inheritance action known as disomy. This is when both copies of a chromosome pair are received from one parent, when usually we receive one copy of each chromosome from each of our parents. This does not always trigger a genetic illness, but when it affects the 3 genes currently identified with Angelman, it triggers the symptoms of this rare disease.

Down syndrome

Down syndrome is perhaps the most well known of all of the genetic syndromes. It is also one of the most prevalent, with around 1 in every 700 babies in the US being born with the condition. The syndrome is the result of the presence of an extra chromosome 21 in affected individuals. This is why it is also sometimes referred to as Trisomy 21. The exact cause of this is not known, although older maternal age is recognized as a risk factor for all chromosomal syndromes. 

The main symptoms of Down syndrome include characteristic facial features – a flat face and nose. Individuals may also experience low muscle tone (hypotonia), mild-moderate intellectual delay and disability, and congenital heart defects. 

Fragile X syndrome

This genetic illness generally affects more males than females, and its symptoms are more severe in males as well. This is due to the way in which it is inherited. As an X-linked disorder, the mutation in the FMR1 gene responsible for the syndrome, occurs on the X chromosome. As males have just one X chromosome, as opposed to females who have two, they tend to be affected more severely by the symptoms of this rare disease. 

This genetic syndrome affects an individual’s intellectual ability and their behavior. 

Marfan syndrome

This genetic disorder has a reasonably high prevalence rate for a rare disease. It occurs in around 1 in every 5,000 live births. It is sometimes referred to as a connective tissue disorder, or a multi-system disorder. The main symptoms of this syndrome affect the skeletal, ocular and cardiovascular symptoms of the body. However not all symptoms are obvious in early childhood, some are not apparent until adulthood. 

The gene responsible for the syndrome is the FBN1 gene located on chromosome 15. It is believed that around 75% cases are inherited, with the remainder being the result of a new genetic mutation. 


The diagnosis of a rare genetic illness can be a long and difficult process. There is still much that is not known about many rare diseases, including their cause and symptoms. The more we understand about genetic syndromes, the more accurately we can diagnose them as well. 




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