Genetic Info about each Disease

HEMOPHILIA

(Many thanks to NHF for much of the following information.)

Hemophilia is a hereditary (genetic) disease - in other words, it "runs in families" (is inherited).

Clotting factor defects are genetic. Genes determine everything physical about a person such as eye color, hair color, and function of clotting factors. Before a baby is born, it receives half of its genetic information from its mother (through her egg cell) and half from its father (through his sperm cell). If the mother or father has the hemophilia gene, it may be passed to the baby through the egg or sperm.

In many cases it can be difficult to tell if a woman carries the gene for hemophilia, but if her father has or had hemophilia, she is called an "obligate carrier," and she carries the hemophilia gene. Boys born to an obligate carrier have a 50-50 chance of having hemophilia, and girls have a 50-50 chance of being carriers (these girls might some day have a baby boy with hemophilia). The odds are the same for each pregnancy.

If a man with hemophilia fathers a child, his sons will not have hemophilia, but his daughters will all be carriers. If a man with hemophilia fathers a child and his female partner is a carrier, the baby could have hemophilia, even if it is a girl. This is extremely rare.

Some children born with hemophilia have no family history of the disease, because genetic changes can occur for no reason. Doctors believe that 30% of all children born with hemophilia have no family history of the disease (the disease occurs spontaneously). But they can pass the hemophilia gene on to their children.

If a woman has a brother, son, or other family member with hemophilia, she may or may not be a carrier. In this case, before getting pregnant, she may choose to get tested to see if she is a hemophilia carrier. Tests look at the woman's clotting factor level and DNA (genetic make-up). They are generally accurate but not foolproof. A woman who considers having these tests should discuss them with her doctor and with a genetic counselor.

A pregnant woman concerned about passing hemophilia on to her baby can have the fetus tested to see if it has hemophilia. These tests (amniocentesis and chorionic villus sampling) are invasive - in other words, tubes or needles enter the woman's body to collect cells from the fetus. Chorionic villus sampling is done during the first trimester of pregnancy, and amniocentesis is done during the second. A woman who considers having these tests should discuss their risks and benefits with her doctor and with a genetic counselor.

VON WILLEBRAND DISEASE

Like hemophilia, the disease is passed down through the genes. But unlike hemophilia, which usually affects only males, von Willebrand disease occurs in men and women equally.

A man or woman with the disease has a 50% chance of passing the gene on to his or her child. Types I and II are usually inherited in what is known as a "dominant" pattern. This means that if even one parent has the gene and passes it to a child, the child gets the
disease. Whether the child has no symptoms, mild symptoms or, less commonly, severe symptoms, he or she definitely has the disease. Regardless of severity of the symptoms, the child can still pass the gene to his or her own offspring.

Type III von Willebrand disease, however, is usually inherited in a "recessive" pattern. This type occurs when the child inherits the gene from both parents. Even if both parents have mild or asymptomatic disease, their children are likely to be severely affected.

These patterns of inheritance differ from hemophilia, which is caused by a defect in one of the "sex-linked" chromosomes. A man with hemophilia cannot pass the gene on to a son, because the abnormality is carried on the X chromosome and a man contributes only a Y chromosome to his male offspring. von Willebrand disease is found on the autosomal chromosomes and therefore can be inherited by either males or females.

von Willebrand disease can often be traced through several generations in a family. Some have symptoms while others just carry the gene.

The chart below shows how quantitative vWD (Type 1 & 3) can be passed down from parents to their children. It should be noted that this chart is a rough guide only. To determine your particular chances of passing down vWD you must consult your doctor or a geneticist.

HEMOCHROMATOSIS

HFE, the gene for classic hemochromatosis was discovered by a team of scientists in California in August 1996. Two major mutations of HFE attributable to iron loading are C282Y and H63D.

Numerous prevalence studies support that mutations of HFE are common among whites. In this population, one in 200-250 are homozygous (have two mutated copies) for C282Y. One in 50 are compound heterozygotes (have one C282Y mutation and one H63D mutation). One in 8-10 are heterozygotes or carriers.

The chart below is a brief example of how HFE mutations occur.