The diseases are neither infectious nor contagious
Epidermolysis Bullosa can be transmitted via the dominant or recessive autosomsal mode. Since the number of sub-types of EB is relatively high, it is possible to encounter both modes of transmission in each of the three main groups (EBS, JEB, DEB)
However,
- Epidermolysis Bullosa Simplex is most commonly transmitted via the dominant autosomal mode
- Junctional Epidermolysis Bullosa is most commonly transmitted via the recessive autosomal mode
- Dystrophic Epidermolysis Bullosa can be transmitted via either the dominant or recessive autosomal mode.
Genetic transmission:
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| The human being is “constructed” on the basis of chromosomes transmitted by the parents. Each person has 23 pairs of chromosomes (1 pair of “sexual” chromosomes or gonosomes, determining the person’s sex, and 22 pairs of autosomes). |
The genes are written onto the chromosomes and it is the expression of the genes that gives each person their particular features. Chromosomes go in pairs. Within each pair, one chromosome comes from the mother and one from the father. Each version is called an allele.
For any given gene the alleles of the two parents can be identical (homozygotes) or different (heterozygotes). If the alleles are heterozygotes, one will express itself over the other: this is called the dominant allele. The other, which is not genetically expressed, is called recessive.
Every genetic illness is caused by a “defect” on one or several genes.
There are two ways in which the defective gene can be transmitted: dominant autosomal and recessive autosomal (links to diagrams to be added). Every pregnancy presents the same risks of transmission.
Dominant autosomal transmission:
When one of the two parents is affected by the pathology, one of their two chromosomes will be affected by the genetic defect. The genetic defect is “dominant” and the parent’s body will display the disease because the gene is expressed. There is a 1 in 2 risk with each pregnancy that the parent will transmit the defective gene to the child, who would then also present with the condition.
Recessive autosomal transmission:
Both chromosomes must carry the defective gene in order for the disease to be expressed. If only one chromosome is affected, the child will become a “carrier”, but will not present with the condition.
Two cases are possible:
- Both parents are healthy carriers: each one carries a recessive pathological allele.
Each pregnancy carries the same risks:
- 1 in 2 chance that the child will be a healthy carrier
- 1 in 4 chance that the child will not be affected at all
- 1 in 4 chance that the child will have the characteristics of Epidermolysis Bullosa
(If only one parent is a healthy carrier, there is no risk of the child developing the pathology).
- One parent presenting with EB
Every pregnancy will produce a child who is a healthy carrier.