Leah Brunnings was a healthy 7-year-old when her 10-month-old brother, Zachariah, was diagnosed with severe hemophilia A. It was 1987, and her parents were baffled. As far as anyone knew, no one in the family had the disorder. Leah’s mother wondered if it could be a new genetic anomaly or if the gene had been in the family tree for generations without anyone knowing it.
In 1998, the family got its answer when Leah’s mother signed up to participate in a clinical trial on hemophilia genetics. Through the trial, the entire family was able to be tested. It turned out Zack’s hemophilia wasn’t a fluke. Leah’s mother was told she had a deletion in her genetic code that causes hemophilia, and Leah’s test results showed she carried the mutation, too.
At the time, Leah filed away the information. She was “asymptomatic,” which meant she showed no physical signs or symptoms of bleeding. At 18, children were not in her immediate thoughts. “I do remember thinking about the implications this would have on the future,” she says. “I knew when I was ready to have kids, it would affect me.”
Until more sophisticated testing methods were developed, many women in the hemophilia community had few clues about their carrier status. Before researchers began discovering the mutations that cause bleeding disorders in the 1980s, doctors tried to determine carrier status by measuring factor levels. The trouble was, that didn’t always produce accurate results.
Through molecular testing, women and their families can now know with certainty their mutation. The identification and diagnosis can help women make better health decisions for themselves and their families. For symptomatic carriers, the diagnosis can prompt them to seek appropriate preventive care or treatment for menorrhagia, dental and surgical procedures, and postpartum bleeding.
“Molecular testing has opened up a world of opportunity to provide a more definitive diagnosis,” says Kristin Pauly-son Nuñez, MS, CGC, a senior genetic counselor at Duke University Medical Center in Durham, North Carolina. “A clear diagnosis gives women more control not only over their own healthcare, but also their reproduction.”
How It Works
Mutations in the gene that causes hemophilia are located on the X chromosome. Males have one X and one Y chromosome (XY), and females have two X chromosomes (XX). Males who inherit an X chromosome with a mutation in the gene (also known as a “change” or “alteration”) have hemophilia. Females who inherit the mutation are carriers for hemophilia, unless both X chromosomes carry the mutation. In that case, they have hemophilia. Carriers can experience bleeding symptoms and can pass on the gene to their children. Although hemophilia is a hereditary condition, about 30% of the time it’s caused by a spontaneous mutation (often in the maternal grandfather of the affected child) with no family history.
There are more than 1,000 mutations each that cause hemophilia A and hemophilia B—and more mutations are being discovered. One type of mutation is an “inversion” of the genetic code, in which sections of DNA are reversed. Two inversions cause 40% to 45% of the cases of severe hemophilia A, says Connie Miller, PhD, team leader for clinical research at the Division of Blood Disorders at the US Centers for Disease Control and Prevention in Atlanta.
Another type of mutation occurs when there are changes to segments of the genetic code. Known as “missense” mutations, they hinder factor VIII (FVIII) and factor IX (FIX) proteins. A “nonsense” mutation causes a premature stop signal, which means that clotting factor protein production is halted prematurely. Nonsense mutations account for approximately 10-15% of hemophilia A and hemophilia B cases, which are typically severe. Other mutations include duplications, in which DNA segments are repeated, and insertions, in which extra pieces of DNA are added. Deletions are mutations in which part of the DNA is missing.
Testing a proven or suspected female carrier often begins by testing an “index patient,” a male in the family with hemophilia. Because women have two X chromosomes, it can be harder to find a hemophilia mutation without knowing the exact type of mutation to scan. Identifying the mutation first on the index patient’s one X chromosome makes testing the woman easier.
Index patients can be a woman’s father, brother, uncle, grandfather or great-uncle with hemophilia, says Carol Kasper, MD, former medical director of the Los Angeles Orthopaedic Hospital. If no male with hemophilia is available for testing, sometimes a known female carrier, or “obligate” carrier, can be tested instead.
Testing a suspected carrier for the family’s known mutation—performing what is called a targeted mutation analysis—often saves money because gene sequencing, which is necessary when the genetic mutation is unknown, can be expensive. It can cost about $2,000 and take eight weeks or longer to run, according to Kasper. Tests to check for specific mutations cost about $250.
Genetic carrier testing starts with a blood draw. Lab technicians use a centrifuge to separate the white blood cells, which contain the important DNA information, from the rest of the blood. The proteins are removed from the cells, and the DNA sequences are extracted from the proteins using alcohol, explains Miller. Then, a technician makes copies of the DNA for the extensive screening to come. If the prescribing doctor suspects the hemophilia was caused by an inversion of the genetic code, the lab tech places the strands of DNA on a gel and passes an electronic current through it to separate the size of the fragments. How the strands break into pieces determines whether an inversion is present, says Miller.
If an inversion is not suspected or known, the lab tech applies “primers,” manmade polymers that attach to different portions of the DNA double helix, to isolate the part where the mutation might exist. The genetic mutation is identified when that section of DNA is compared with a normal section of DNA.
Deciding Whether to Test
All women do not need to be tested to confirm their hemophilia carrier status. Enid Carter, 43, a massage therapist from Dearborn Heights, Michigan, knew she was an obligate carrier, the daughter of a man with hemophilia. (Daughters of men with hemophilia are carriers or have hemophilia themselves.) Still, she felt the test was important to explain why she had blood in her urine, which turned out to be from bleeding in her kidney.
Further, she was able to determine the mutation for her entire family line. “I realized as an obligate carrier, the testing was valuable for those I might pass the information along to,” she says. “As women, we really need to start writing our own histories down.”
Other women who may want to have a genetic test include those with a family history of bleeding disorders who are considering pregnancy or who are already pregnant, Nuñez says. Known symptomatic carriers with no family history may also want to know their mutation, according to “Hemophilia: A Practical Approach to Genetic Testing.” The article was published in Mayo Clinic Proceedings in 2005 by Rajiv Pruthi, MBBS, associate professor of hematology at the Mayo Clinic in Rochester, Minnesota. “In symptomatic carriers with no family history of hemophilia, and thus no information on clinical phenotype, genotyping of the carrier and/or fetus or child can predict severity of the disease,” Pruthi wrote. This is also true for adopted women who are carriers and unaware of their family history.
What’s more, some women can have normal factor levels but still experience bleeding symptoms, says Danielle Nance, MD, fellow in hemostasis and thrombosis at the Puget Sound Blood Center and University of Washington in Seattle. She is a symptomatic carrier from a spontaneous mutation and mother of a son with severe hemophilia A. A March 2011 study in the journal Haemophilia found that women who are carriers of severe mutations (inversions or deletions) in their FVIII genetic code are two to three times more likely to have bleeding problems, even if their FVIII levels are in the normal range of 40% to 80%.
“That result wasn’t something we expected,” says Nance. “We always knew that if a woman’s factor VIII level was below 30% or 35%, she had an increased chance of bleeding. Now it looks like even if the factor level is in the normal range, a woman could have an increased risk of bleeding if she has a severe mutation.” The study did not examine FIX mutations.
Suzanne Swietnicki, MD, an ob/gyn at Northern Montana Medical Group in Havre, agrees that knowing your genetic code makes it easier on everyone when you have surgery or during childbirth. “The last thing we want is a carrier woman to end up in an emergency room and be seen by someone not familiar with bleeding disorders or be treated inappropriately surgically,” she says.
Testing During Pregnancy
For those who are already pregnant, carrier testing is safe and effective. All it takes is a simple blood test. It’s also the only definitive way to tell a woman whether she’s a carrier. Further, the test identifies her mutation, which allows doctors to test the fetus using amniocentesis.
But not everyone opts for a genetic test, says Pruthi. The wait time for the test results and the cost often cause people to choose to compare FVIII, FIX and von Willebrand factor (VWF) levels instead. If low enough, those levels can indicate that a woman might be a carrier without the need for expensive molecular tests, says Pruthi. However, FVIII and VWF levels increase during pregnancy, so a woman could believe she’s not a carrier when she is. (FIX levels aren’t affected by pregnancy.) The DNA test is the gold standard, Kasper says. It’s the only way to definitively prove that a woman or her fetus is not a carrier.
Health insurance providers, including Medicaid in many states, may not cover genetic testing. However, such testing is not always spelled out in insurance policies. It’s important for women to advocate for coverage for themselves—and perhaps for the affected male in their family—with the insurance company. They may want to enlist the help of their hemophilia treatment center or hematologist. It is up to women and their doctors to make a clear case about why they need the test.
“With insurance companies, it’s always a bottom-line issue. If they step up and help this one time, it could be over with the one test,” Pruthi says. “It would benefit the whole family, not just the one individual.”
Ethical Issues of Testing Girls
Knowing their status helps women who are carriers take control of their lives in a way they couldn’t otherwise. Leah decided after a miscarriage to undergo preimplantation genetic diagnosis to select zygotes that did not have hemophilia and weren’t carriers. Her 15-month-old daughter, Allison, is a product of those tests. “I just couldn’t see myself having the strength to go through all that with my own child if I had a chance to avoid it,” says Leah, recalling the strain and confusion her own mother experienced.
Leah wants Allison to be tested, if only to ease her own mind. When Allison was 1 year old, Leah asked her doctor if she could test her to make sure she wasn’t a carrier. The doctor said it would be difficult to draw enough blood from an infant for such a test and it wasn’t entirely necessary, as Allison wasn’t having any symptoms. Leah still plans to test Allison in the next few years.
However, national and international organizations are concerned about testing children for hereditary disorders. The American College of Medical Genetics issued a statement in 1995 recommending that genetic counselors and doctors not give genetic tests to children who could be carriers of any hereditary disease if they don’t have symptoms themselves. Doing so, they argued, could cause psychological harm.
Further, the United Nations Convention on the Rights of the Child has stated that any action or decision that affects children should be in their best interests, according to a 2010 study in the Journal of Pediatric and Adolescent Gynecology. “A view is now evolving both in the UK and the USA that the motivation for testing children should be to improve their medical care, rather than to obtain reproductively significant information,” the journal authors wrote.
Some also argue that young girls should be old enough to agree to the blood test and understand the implications if it’s positive. But it’s also recognized that there’s a difference in the ability to understand medical tests and make informed decisions between, for example, a 5-year-old and a 15-year-old.
“Testing daughters who are at risk of being carriers is a gray area,” Nuñez says. There’s no consensus on what age is appropriate to test a girl to learn if she’s a carrier. “I think it makes sense to consider testing girls if they are presenting with symptoms,” she says. “It may be able to provide clinical evidence in the management of their disease.”
Whether a woman is seeking to learn if she’s a carrier or to define her gene mutation, knowing her hemophilia status can allow her to make informed decisions about her healthcare. “When you have the results, you can decide how they will affect your life and prepare yourself for whatever they might mean,” Leah says. “It’s important to know about yourself so you’ll have the resources when your carrier status comes into play.”