GENETICS
The Genetics of EB
This will be my attempt to explain the genetics of EB in terms that the average person can understand.
EB is an inherited condition.
Essentially, someone with EB is missing the "glue" that holds the skin together.
Recessive forms of EB:
Those include:
All forms of Junctional EB
Recessive Dystrophic EB
Two forms of EB Simplex(EBS-PA and EBS-MD
And a newly discovered form of EB called Kindler Syndrome
In these types, the person with EB received 2 mutations, one from each parent. In recessive EB, it takes 2 copies of any EB mutation to cause EB to develop. That is why the parents do not have EB; they just have one copy of the gene. But when each of those copies is put together, it causes recessive EB.
With recessive EB, there is a 25% chance with each pregnancy
that the baby will have EB.
Testing for Recessive EB
In testing for recessive EB, the lab will try to locate the two mutations in the child with EB. After those mutations are found, they will look in the DNA of the parents to see if they are recessive carriers. Once this is complete, you can use this information for prenatal testing in future pregnancies, or if you have other children, have them tested to see if they carry one of the mutations, so they will know for future reference when they grow up and have kids. Remember that with recessive EB, it takes 2 mutations to cause EB, so if your other child(ren) only has one of the mutations, it means they do not have EB, but carry a mutation that can cause EB.
Dominant forms of EB:
Those include:
Dominant Dystrophic EB
Most of the EB Simplex forms.
In these types, it only takes 1 EB mutation to make Dominant EB. Typically, one of the parents has EB and then passes it on to their child. In this case, there is a 50% chance with each pregnancy that the baby will have EB.
Dominant forms of EB can also occur when a spontaneous mutation occurs at conception. No one knows why this occurs; it just does. There is nothing you ate, drank, did, or did not eat, drink or do that caused this; it just happened.
Testing for Dominant EB:
In testing for Dominant EB, the lab will look for the mutation in the child. Once that is found, they will compare it to the DNA of the parents.
If they do not find the mutation in either parent, then this was a case of spontaneous mutation.
In the case of spontaneous mutation, the parents of the affected child have a
2-3% chance of having another child with EB. This is due to gonadal mosaicism.
Visual Diagnosis of EB
You may have found that many doctors will try to tell you what type of EB your child has just by looking at them. That is usually a very unreliable way to diagnose a child with EB.
In my experience and observation of babies and children with EB, typically those with recessive forms of EB tend to start out milder in the beginning and get worse as they get older.
Typically, those with dominant forms of EB tend to start out more severe at birth and get better as they get older.
But everyone with EB is different, and no two people will present the same way or progress the way the "experts" say they will based on the type of EB they have.
*NEW*
A procedure called PGD-IVF is available to those families wishing to have an EB-free child. You can learn more about the process here
Genetic Testing:
Molecular genetic studies (DNA analysis) are a must for a more accurate diagnosis of EB. Molecular studies are done to
identify the specific genetic mutation and to determine the mode of
inheritance (recessive vs. dominant). There is a new genetic test that
tests for ALL known EB mutations in one sample: It is called the Epidermolysis Bullosa (EB) XomeDx®Slice
Below are the labs in the US that can perform genetic testing for EB.
1) GeneDx
207 Perry Parkway
Gaithersburg, MD 20877
301-519-2100
www.genedx.com
2) Prevention Genetics. Currently, EB genetic testing through this lab is FREE for those who live in the United States.
EB Statistics
The incidence column estimates the number born in a given year. The last official birthrate numbers are from 2009, and that year it was 4,130,665 (2010 and 2011 are not available)
Material is based on the NEBR study population
| EB type or subtype: | Prevalence* | Incidence** | | | | | | | | | |
| EB (All types and subtypes, including unclassified patients) | 8.22 | 19.60 |
| EBS | 4.60 | 10.75 |
| EBS, Localized (formerly Weber- Cockayne) | 3.14 | 6.81 |
| EBS, all others | 1.46 | 3.95 |
| JEB | 0.44 | 2.40 |
| JEB-Herlitz | 0.07 | <0.41 |
| JEB, other | 0.37 | <2.04 |
| DDEB | 0.99 | 2.86 |
| RDEB | 0.92 | 2.04 |
| RDEB, severe generalized (formerly Hallopeau- Siemens) | 0.42 | 0.41 |
| RDEB, all others | 0.49 | 1.63 |
*Prevalence of EB patients per one million births (1990)
**Incidence of EB births per one million live births (1986-1990)
Fine, Jo-David and Hintner, Helmut. (2008) "Life with Epidermolysis Bullosa (EB): Etilogy, Diagnosis, Multidisciplinary Care and Therapy" Springer-Verlag/Wien, New York.
The number in the Incidence Column is per 1 million births, so to find the actual number of new cases of EB each year in the US, multiply that number by 4.13 (the approximate total number of births in the US each year)
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