TRAINING and EDUCATION
Demystifying the Lab
approximately 30 percent of patients with
hemophilia A develop inhibitors to FVIII
infusions, making their treatment extremely
difficult to manage. 5
Several factors, both genetic and environmen-
tal, are thought to increase the likelihood that
a patient develops inhibitors, but accurate risk
prediction remains a challenge. Specific genetic
mutations, like FVIII(null), have been associated
with inhibitor development; so, if genetic testing
reveals that a patient has such a mutation, a clini-
cian can discuss the risk with the patient and his
family to decide whether an alternative treatment
such as emicizumab (a monoclonal antibody that
can substitute for FVIII but doesn’t resemble the
protein itself) might be a better option than fac-
tor replacement.
Genetic testing also can be a valuable tool
in guiding treatment decisions in patients who
experience “spontaneous bleeding or who
have no family history of bleeding disorders or
whose family history is unknown,” Dr. Doshi
added. In those instances, she said, “we will –
after fighting with insurance – try to get genetic
testing done in patients with severe hemophilia
[to find out if] this a mutation that’s associated
with inhibitors.”
Genetic Testing for All?
Results from genetic tests can reveal impor-
tant information, but the experts interviewed
agreed that clinicians need a better under-
standing of whom to test – and what to look
for. “There is more and more to be learned
that sometimes only the genetic testing will
reveal. That said, it makes sense to do the right
testing for all patients,” Ms. Dugan noted.
The technology used to identify the most
common genetic variants involved in hemo-
philia is readily available to most laboratories,
but Ms. Dugan advised that clinicians consult
experts in hematologic genetics to ensure that
the appropriate tests are ordered and that the
results are interpreted correctly.
“It is important that the clinician, as well as
the patient and the patient’s family, appreciate
what has been tested,” she said. “I have worked
with providers who have ordered what they
thought was ‘hemophilia genetic testing’ and
received a negative result, but they learned
later that they had really only ordered one part
of the hemophilia testing.” The test may come
back negative, she explained, but only for one
pathogenic variant associated with that condi-
tion. “So, while that part was negative, they
actually had to order a different test – the right
test – to identify the cause of hemophilia in
that family,” she added.
In vWD, there are fewer instances where
genetic testing is justified, “because the clinical
impact of genotyping in [this disease] hasn’t
really been clear,” according to Steven Pipe,
MD, director of the coagulation laboratory at
Michigan Medicine and chair of the medical
and scientific advisory council of the National
Hemophilia Foundation. Because the disease-
causing vWF gene is so large and contains more
than 300 single nucleotide polymorphisms,
it is difficult to sequence, and results from
genetic testing don’t always provide conclusive
answers. 6
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ASH Clinical News
However, in some situations, genetic test-
ing is justified because its results could aid in
genetic counseling or help guide treatment
decisions, as with vWD type 3, where iden-
tifying certain deletions can predict which
patients are at a higher risk for developing
neutralizing antibodies. In these situations,
mutations are typically clustered in specific
areas of the vWF gene, simplifying sequenc-
ing and interpretation.
As Dr. Doshi noted, genetic testing is rarely
covered by insurance, so advocacy organiza-
tions have begun partnering with academic and
hemophilia treatment centers to genotype large
numbers of patients and grow the genomic
database.
For example, in 2012, the American
Thrombosis and Hemostasis Network, National
Hemophilia Foundation, and Bloodworks
Northwest partnered to launch the My Life,
Our Future program to offer genetic testing
to patients with hemophilia at low or no cost. 7
Their stated goal was to create the world’s
largest genetic hemophilia repository, which
would eventually help scientists answer ques-
tions about why the disease’s severity differs
widely among patients, who is likely to develop
inhibitors, and which genes will be optimal
targets for gene therapies. My Life, Our Future
participants also can elect to have their genome
sequenced through the National Institutes
of Health’s National Heart, Lung and Blood
Institute’s Trans-Omics for Precision Medicine
(TOPMed) Program. 8
So far, the program has genotyped nearly
10,000 patients with hemophilia, and Dr. Pipe
reported that the program has identified near-
ly 700 previously unreported variances caus-
ative for hemophilia. “This has provided a rich
resource for investigators who study molecular
mechanisms in hemophilia,” he said, “and they
can start to tackle some of the questions about
previously unknown mutations.”
The Promise of Gene Therapy
The end goal of collecting genetic sequencing
data from a large group of hemophilia patients
is to understand the disease fully so that it can
be cured on a genetic level. Gene therapy has
been on the radar for decades, especially for
diseases, like hemophilia, that are caused by a
mutation in a single gene; now, researchers are
getting closer than ever to that dream.
Methods to “correct” faulty genes using
viral vectors have been used in the laboratory
in model organisms since the 1950s, but only
recently have researchers begun testing them
in humans. Currently, there are three gene
therapy candidates for hemophilia in phase III
clinical trials: valoctocogene roxaparvovec for
hemophilia A and AMT 061 and fidanacogene
elaparvovec for hemophilia B.
These therapies all rely on engineering
recombinant adeno-associated virus (rAAV)
vectors to carry a gene of choice to “invade”
the genome of another organism. For hemo-
philia, that means using the technology to de-
liver functional FVIII and FIX genes to replace
defective genes.
Although the progress is promising, few
gene therapies actually have been approved
for any genetic diseases because there are
myriad difficulties in engineering a vector able
to carry enough of the functional genes and
insert them in the appropriate places at the ap-
propriate times. In early-phase trials, research-
ers found that many patients had dangerous
inflammatory responses to the vectors.
The efforts are further complicated by
the complexity of the FVIII and FIX genes.
Each is large – too large to fit into the vector.
FVIII, the gene that is dysfunctional in the
more common hemophilia A, is especially
large, so most early advances in gene therapy
were made for treatments of hemophilia B.
Recently, scientists have found that truncated
versions of the genes can fit inside the vectors,
and while they may not be as desirable as a
fully functional gene, they may be able to
improve patients’ symptoms.
For vWD, researchers are adopting a dif-
ferent approach to using genetic technologies.
Rather than delivering a fully functional gene,
Dr. Swystun described a “workaround” being
explored by some scientists. “For example,
they now are making portions of the vWF pro-
tein that can bind to FVIII independently of
the full-length vWF protein, [suggesting] you
might be able to treat some patients with this
fragment [instead of the whole gene],” he said.
There is still a long way to go before
gene therapy finds its way to routine clinical
practice. And there are still limitations to gene
therapy for inherited disorders; for one, while
gene therapies may be able to help patients,
they will not prevent them from passing the
dysfunctional gene on to their own children
in the future. Most investigational therapies
have been tested only in adults at this point,
and more studies are needed to determine the
safety of these treatments in younger patients.
Still, researchers are optimistic. “We should
see results from the three phase III trials in the
not-so-distant future, hopefully followed by an
approval not too much later,” Dr. Doshi said.
“I think it’s very close.” —By Emma Yasinski ●
REFERENCES
1. National Hemophilia Federation. “History of Bleeding
Disorders.” Accessed February 27, 2019, from https://www.
hemophilia.org/Bleeding-Disorders/History-of-Bleeding-
Disorders.
2. Centers for Disease Control and Prevention. “Diagnosis of
Hemophilia.” Accessed February 27, 2019, from https://
www.cdc.gov/ncbddd/hemophilia/diagnosis.html.
3. National Human Genome Research Institute. “Learning
About Hemophilia.” Accessed February 27, 2019, from
https://www.genome.gov/20019697/learning-about-
hemophilia/.
4. Swystun LL, James P. Using genetic diagnostics in
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5. Hemophilia Federation of America. “Inhibitors.” Accessed
February 27, 2019, from https://www.hemophiliafed.
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6. Ng C, Motto DG, Di Paola J. Diagnostic approach to von
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7. My Life, Our Future. “Research.” Accessed February 27,
2019, from http://www.mylifeourfuture.org/research.
html.
8. National Heart, Lung, and Blood Institute. Trans-Omics for
Precision Medicine (TOPMed) Program. Accessed February
27, 2019, from https://www.nhlbi.nih.gov/science/trans-
omics-precision-medicine-topmed-program.
May 2019