Inheritance of lymphedema
Lymphedema is the swelling, usually of an extremity, resulting from poor drainage of fluid out of the body's tissues. There are two types of lymphedema. Although the cause is not well understood, primary lymphedema is thought to result from an inherited abnormality of the lymphatic system. Secondary lymphedema is the result of a damaged or blocked lymphatic system caused by traumas such as surgery or injury.
Primary lymphedema has been estimated to occur in about 1 in 6000 people, more often in females than in males (Dale, 1985). Age of onset tends to be similar within families. Primary lymphedema can be present from birth (congenital lymphedema or Milroy's Disease), symptoms can begin at the time of puberty (lymphedema praecox or Meige's Disease), or onset can occur in adulthood (lymphedema tarda) (Lewis and Wald, 1984).
Primary lymphedema seems to be inherited in several different ways. Milroy's and Meige's Disease are two forms of primary lymphedema that tend to show swelling below the waist and are dominantly inherited in some families. Milroy's Disease (congenital lyphedema) is characterized by swelling present from around the time of birth. Meige's Disease, also known as lymphedema praecox, may appear suddenly around the time of puberty (Wheeler et al., 1981). When the first signs of swelling appear after age 35, this condition is called lymphedema tarda. A recessive form of lymphedema has also been described, as well as lymphedema in association with other traits (syndromic lymphedema).
Except for genes on the sex chromosomes, both men and women have two copies of each gene. If only one altered copy of a gene (mutation) causes a condition, the condition will be inherited in what is called a dominant pattern. If an individual has a dominant condition such as Milroy's or Meige's Disease, the chance of passing the gene to a child is 1 in 2 or 50% with each pregnancy. These odds are the same as getting "heads" in a coin toss.
Dominant disorders are ones that run from generation to generation or are passed along through the family. If a person has the mutation for a dominant form of primary lymphedema, there is usually a 50% or 1 in 2 chance of passing that mutation on to his or her children. However, not everyone with the mutation for this form of lymphedema will actually develop symptoms. Therefore, even if a child does not inherit lymphedema from a parent, he or she may still have inherited the mutation and pass the mutation that causes lymphedema on to a child. Although we do not yet understand why this "reduced penetrance" sometimes occurs, it is more common in men. In other words, a brother would be less likely than his sister to have symptoms of lymphedema even if they both inherit the same lymphedema mutation.
We hope a new understanding of the genetic basis of inherited lymphedema will provide insights into its treatment and contribute to early identification of individuals at risk.