Understanding Genetic Inheritance in EDS

By Barbara Uggen-Davis

Just because you have EDS, doesn’t mean your kids will automatically have EDS too. Before deciding whether or not to have children, it is a good idea to learn about the genetic inheritance patterns associated with your type of EDS. It may also help to spend some time talking to a genetic counselor to address any concerns you have about genetic inheritance. The following is an overview of how EDS may be inherited.
There are six types of EDS, but not all types of EDS are inherited in the same manner. There are two inheritance patterns associated with EDS: autosomal dominant and autosomal recessive. In addition, some cases of with EDS result from a new genetic mutation, in which there is no family history of EDS.

Autosomal Dominant Types of EDS

The most common types of EDS are inherited in an autosomal dominant pattern. The Hypermobility Type, Classical Type, Vascular Type, and Arthrochalasia Type are all autosomal dominant. Hypermobility is the most common form of EDS, affecting between 1 in 10,000 to 15,000 people. Classical Type affects between 1 in 20,000 to 1 in 40,000 people. The Vascular type affects between 1 in 100,000 to 200,000 people. Half of the people with this type of EDS inherited it from a parent, while the other half of EDS cases resulted from a new genetic mutation. Finally, the Arthrochalasia type is reported to affect fewer than 30 people worldwide.

Autosomal Recessive Types of EDS

The rarest forms of EDS are inherited in an autosomal recessive pattern. Kyphoscoliosis type is reported to affect fewer than 60 people worldwide and the Dermatosparaxis type, less than 10 people.

Basic Genetics

Each person has 46 chromosomes. We inherit 23 from our father and 23 from our mother. Of the chromosomes we inherit from each parent, 22 are autosomes, which are the same for both men and women, and 1 is a sex chromosome which is designated either X or Y. Women inherit two X chromosomes and men inherit one X and one Y chromosome. Each chromosome contains thousands of genes. These genes determine our traits, such as hair color, eye color, height, and other characteristics. Genes are also responsible for disorders, such as EDS. The genes we inherit from one or both of our parents determines whether or not we have EDS.

Autosomal Dominant Inheritance

In autosomal dominant inheritance, only one copy of the EDS gene needs to be passed to the child in order for the child to have EDS. Let’s say the mother has EDS. She has 46 chromosomes, but will only pass half of the chromosomes to the child. She will have one EDS gene and one non-EDS gene. There is a 50% chance that she will pass the EDS gene to the child, meaning the child has a 50% chance of having EDS. The EDS gene overrides or dominates the healthy gene. The majority of EDS types are autosomal dominant.

Autosomal Recessive Inheritance

In rare types of EDS, the inheritance pattern is autosomal recessive. In recessive inheritance, there must be two copies of the bad gene in order for the person to have EDS. If the mother has a recessive type of EDS, she has two copies of the EDS gene. Because she does not have the non-EDS gene, she is guaranteed to pass the gene to her child. However, the father must also pass a copy of the EDS gene to the child in order for the child to have EDS. The father might not have EDS symptoms, but could be a carrier of the EDS gene, meaning he has only one copy of the gene.

X-Linked Recessive

Another type of genetic inheritance you may have heard about is called X-linked Recessive. At one time, there was an EDS type that was X-linked Recessive. This type has been reclassified and is no longer considered part of the Ehlers-Danlos Syndromes. X-Linked Recessive is an inheritance pattern that is related to the X-Chromosome. Like autosomal recessive inheritance, you must inherit two copies of the gene in order to have the disorder. Because the gene is on the X-Chromosome, only people who inherit two X-Chromosomes (women) will have the disorder.

Mutation

Sometimes people have EDS when there is no history of EDS in the family. If the EDS type is not a recessive type, then it is most likely that the individual has EDS as a result of a new genetic mutation. Each gene is made up of a series of bases, which form the instructions for making a single protein. There are four bases, designated A (adenine), T (thymine), G (guanine), and C (cytosine). A mutation is a change in the sequence of the bases that form a particular protein. Imagine that the bases form words, and each word represents a protein. A mutation occurs when one of the words is misspelled. Approximately half of the cases of Vascular type EDS are the result of a new mutation.

Genetic Counseling

Genetic counseling is a valuable tool for people with genetic conditions. Genetic counselors are educated about numerous genetic conditions and can help patients understand genetic inheritance patterns. Where appropriate, genetic counselors recommend and arrange for genetic testing and help explain the test results. If you have questions about having children, a genetic counselor may help provide guidance and support.

References

• Ehlers Danlos Syndrome, Genetics Home Reference, Accessed March 4, 2004

• Adams, A., Genetics 101 Overview of Genetics, Accessed March 9, 2004,

• Adams, A, Resources, What is Genetic Counseling?, Accessed March 9, 2004,

Websites on Genetic Inheritance and EDS

• Ehlers-Danlos Syndrome: Causes (University of Washington, Orthopaedics & Sports Medicine)

• Hereditary Patterns in Ehlers-Danlos Syndrome (EDNF)

• Human Genome Education Model Project II: Fact Sheet #15 Non-Traditional Inheritance I

• Genetic Drift: Non-Traditional Inheritance

• Mutation Analysis in Various Types of Ehlers-Danlos Syndrome (EDS).

• Ehlers Danlos Syndrome, Genetics Home Reference

• Genetics 101 Overview of Genetics

• Resources, What is Genetic Counseling?

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