National Foundation for Ectodermal Dysplasias

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ectodermal dysplasias through education, support, and research.

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Genetics

Are the ectodermal dysplasias hereditary?

Yes, the ectodermal dysplasias are hereditary. You must know a few things about genetics in order to understand how the ectodermal dysplasia syndromes are inherited.

The body is composed of billions of cells. Each cell has within it a small central structure called the nucleus. Within the nucleus are chromosomes, which are small thread-like strands of hereditary material (DNA). The chromosomes, in turn, are composed of genes. It is easy to understand the concept of genes by thinking of a cell as a jewelry box and the nucleus as one of the drawers in the box. The chromosomes, then, can be considered as necklaces in the drawer, and the genes as the individual beads on each necklace.

The ectodermal dysplasias are caused by alterations in genes. Altered genes may be inherited from a parent, or normal genes may become altered (mutate) at the time of egg or sperm formation or after fertilization. It is important to remember that a person cannot choose or modify the genes that he or she has, and that conception and events of pregnancy by and large do not change the genes. Thus, parents who have a child with an ectodermal dysplasias should not think that they did anything to cause the ectodermal dysplasias and cannot blame themselves or take credit for its occurrence.

The chances for parents to have affected children depend on the inheritance pattern of the type of ectodermal dysplasia that affects the family. The next section highlights these chances but cannot explain them well enough to cover all cases. Thus, a family affected by an ectodermal dysplasias should consider conversations with a geneticist or a genetic counselor for a better understanding of the specific ectodermal dysplasia and for information about the spectrum of the specific condition and the probabilities or risks that the ectodermal dysplasia will occur in any future pregnancy.

Parents of affected children should ask how the ectodermal dysplasia is inherited. Are they at risk to have other affected children? Can the children with ectodermal dysplasia pass it on to their children? Can other individuals in the family be more severely affected? What other relatives are at risk to have affected children? These questions cannot be answered without a correct diagnosis and without knowledge of the inheritance pattern in the family.

How Inheritance Works

New Mutation

Generally, when a mutation has occurred, there is little chance that it will occur in another child of the same parents. The affected child may transmit the trait, however.

Autosomal Dominant

When the ectodermal dysplasia is an autosomal dominant trait, the parent who is affected has a single copy of the abnormal gene and may pass it on to his or her children. Regardless of the gender of the parent or the child, there is a 50% chance for each child to receive the abnormal gene. All children who receive the abnormal gene will be affected.

Autosomal Recessive

When the ectodermal dysplasia in the family is an autosomal recessive trait, the usual situation is that each parent is unaffected. The parents are said to be carriers. They each have a single copy of the abnormal gene and the chance for them to have another affected child is 1 in 4 (1 in 4 children get a copy of the abnormal gene from each parent and is affected; 2 in 4 gets only one copy each and are carriers, and the remaining 1 in 4 inherits a normal gene from each parent and is not affected).

X-Linked Recessive

If a woman is a carrier of an X-linked recessive disorder, there is a 50% chance that each male child will receive the abnormal gene and be affected and a 50% chance that each female will receive the abnormal gene and be a carrier (like the mother).

If a man has the abnormal gene, he is affected and will pass the gene on to all of his daughters. The daughters will be carriers. Since the gene is on the X chromosome, sons will not be affected because they receive the man’s Y chromosome.

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