Tuesday, October 23, 2012

Inheritance....

How is EB Inherited?


All the genes of a human body come in pairs. We receive one half from our mother and the other half from the father. Genetic disorder such as Epidermolysis Bullosa (EB) is passed to a child from the mother and/or father's chromosomes. All of the genes that cause EB are autosomal i.e. the genes are not carried on the sex-determining (X and Y) chromosomes. Chromosomes are two sets of instruction manuals that contain information on how to make everything in our body. One instruction manual is from our mother and the other is from our father. Genes on chromosomes are like pages or sections of the instruction manual that focus on a specific part of the body, like eye color.

 In individuals with EB, some of the pages (genes) of one or both instruction manuals (chromosomes) are missing or incorrect. These pages should contain the instructions to make the proteins that hold the skin together. Faulty instructions lead to missing or abnormal proteins and the skin is not as strong as it should be. One or two sets of bad instructions produce different forms of EB.
Autosomal Dominant Inheritance

Most forms of EB Simplex and Dominant Dystrophic EB are autosomal dominant - only one mutated gene is enough to develop the disease. The mutated gene is able to disrupt the function of the normal gene. The parent from whom the sufferer inherited the mutated gene also has the symptoms of the conditions.

A person with a dominant form of EB has a 50% chance in each pregnancy of passing the disease on to their child.

A person may have a dominant form of EB and not have an affected parent. In these cases, a new mutation in the egg or sperm of one parent occurred.



Autosomal Recessive Inheritance

All forms of Junctional EB and Recessive Dystrophic EB are autosomal recessive - two abnormal genes are needed to produce disease.
A carrier has one copy of mutated gene for the disease and is completely healthy. If a carrier has a child with another carrier for the same disease, their child may be affected. When two carriers for a disease produce a child, there is a:
  • 25% chance the child will have the disease
  • 50% chance the child will be a carrier
  • 25% chance the child will have completely normal genes.




This information is most useful to parents who have had one child with a recessive form of EB in determining their risk of having another affected child in the future.



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