Becky Abbott, MPH is Manager of Treatment and Research at the National Foundation for Ectodermal Dysplasias (NFED) which provides comprehensive services to individuals affected by ectodermal dysplasias and their families.
Ectodermal dysplasias (ED) are a group of more than 180 disorders that affect the outer layer of tissue of the embryo (ectoderm) that helps make up the skin, sweat glands, hair, teeth, and nails. Symptoms of ED can range from mild to severe and may include teeth abnormalities; brittle, sparse or absent hair; abnormal fingernails; inability to perspire (hypohidrosis); various skin problems; and other symptoms. Different types of EDs are caused by mutations in different genes, and can be inherited in a variety of ways. No cure currently exist for the different types of ED, but many treatments are available to address the individual symptoms.
Ectodermal dysplasias are genetic disorders, which means that they can be passed on from affected people to their children. They are caused by mutations in various genes; the mutations may be inherited from a parent, or normal genes may become mutated at the time of egg or sperm formation, or after fertilization. The risk for parents to have an affected child depends on the inheritance pattern of the specific type of ectodermal dysplasia with which the individual in the family has been diagnosed. Thus, a family affected by an ectodermal dysplasia should consider speaking with a geneticist or a genetic counselor for a better understanding of the specific ectodermal dysplasia and the probabilities or risks that the ectodermal dysplasia will occur in any future pregnancy.
The different types of inheritance patterns that occur depending on the specific type of ectodermal dysplasia in the family include x-linked recessive, autosomal dominant, and autosomal recessive.
X-linked recessive: If a woman is a carrier of an x-linked recessive form, there is a 50% chance that each of her male children will inherit the mutated gene and be affected, and a 50% chance that each female will inherit the mutated gene and be a carrier (like the mother). If a man has the mutated gene, he will be affected and will also pass the gene on to all of his daughters, who will be carriers. Since the gene is on the X chromosome, his sons will not be affected because they receive the man’s Y.
Autosomal dominant: When the ectodermal dysplasia is an autosomal dominant form, the parent who is affected has a single copy of the mutated gene (which is sufficient to cause the disorder in any autosomal dominant condition) 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 mutated gene and be affected, and a 50% chance to not inherited the mutated gene. All children who receive the mutated gene will be affected.
Autosomal recessive: When the ectodermal dysplasia in the family is an autosomal recessive form, the usual situation is that each parent is unaffected, but likely has one mutated copy of the gene and one normal copy of the gene. They are said to be carriers. Carriers do not typically show signs and symptoms of an autosomal recessive condition. When two parents who are carriers have children, with each pregnancy there is a 25% (1 in 4) risk for the child to have the condition, a 50% (1 in 2) risk for the child to be an unaffected carrier like each of the parents, and a 25% chance for the child to not have the condition AND not be a carrier (and therefore not pass the mutation on to future generations). To be affected with an autosomal recessive condition, an individual must have two mutated copies of the disease-causing gene.
Sometimes, when an individual is the first person in a family to be affected with an ectodermal dysplasia, it is because a new mutation occurred in that individual, and neither of the parents carry a mutated copy of the gene. Usually, in this case, there is little chance (about 1%) that it will occur in another child of the same parents. However, the affected child may transmit the disease-causing gene to future generations. It is also important to know that even in families and individuals who have the exact same mutation, there can be variability in how the condition affects each family member.