Portada Simposios - Supplements - Haematologica

130 Haematologica (ed. esp.), volumen 85, supl. 2, octubre 2000
when using a single plucked hair as a source of genomic
DNA, thus evidencing the high sensitivity of
the procedure.
Prenatal diagnosis of hemophilia, requested when
the fetus is at risk, has been traditionally performed
from chorionic villus samples because they can be
obtained earlier in pregnancy than amniotic fluid. To
offer an additional possibility, we have successfully
adapted our procedure to the diagnosis of hemophilia
from amniotic fluid obtained at very early stages
of gestation by amniofiltration. This obstetric
procedure is based on collection of the cellular fraction
of the amniotic fluid in early stages of embryonic
development by a closed system that returns almost
all the volume to the amniotic sac after filtration.
This procedure allows recovery of an adequate
number of nucleated cells after the 11 th week of gestation,
with minimal risk of altering fetal development.
Since both the PCR-based inversion study and
the direct fluorescent DNA sequence are powerful
and sensitive methods, the small amount of genetic
material obtained is enough to carry out an accurate
prenatal diagnosis.
To sum up, precise determination of the gene defect
is the only way to explain the ultimate basis of
hemophilia And the biochemical events involved in
this pathology. Our direct-sequencing approach,
which has proved to be rapid, sensitive and cost-effective,
leads us to suggest that this procedure is the
best option for high-quality molecular diagnosis of
hemophilia. Moreover, direct sequencing allows precise
genetic counseling and reliable prenatal diagnosis
without the intrinsic limitations of linkage
analysis.
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ROLE OF GENE THERAPY
IN THE TREATMENT
OF HAEMOPHILIACS
G. HORTELANO
Canadian Blood Services and Department of Pathology
and Molecular Medicine, McMaster University, 1200 Main
Street West, Hamilton, ON L8N 3Z5, Canada.
Haemophilia is a bleeding disorder caused by a
deficient factor VIII (FVIII) in haemophilia A, or factor
IX (FIX) in haemophilia B. Current treatment, based
on regular life-long infusions of plasma-derived
or recombinant factors is suboptimal 1 . An alternative
would be highly desirable. Gene therapy could be
such alternative. There are a number of factors that
make haemophilia a disease particularly suitable to
be treated by gene therapy:
1. Factor concentration in plasma is not tightly regulated,
making delivery feasible. Delivery of supraphysiological
levels of coagulation factors (up to
several-fold the physiological levels) cause no apparent
adverse effects in haemophilic animals 2,3 . This is
important, because it is reasonable to anticipate significant
individual variation in response to gene therapy
protocols.
2. Even partial restoration of the levels of coagulation
factor can be of clinical benefit. Indeed, delivery
of as low as 0.1 % of the normal FIX plasma levels had
some clinical effect in haemophilic dogs 4 . This finding
suggests that patients will benefit from even the
smallest amount of coagulation factors delivered.
3. Even though the liver is the principal organ for
FVIII and FIX synthesis in humans, synthesis and secretion
from a different cell type could restore coagulation
activity in haemophiliacs provided the delivered
clotting factors are biologically active and have
access to the circulation 5 .
4. Finally, there are excellent animal models of haemophilia.
Murine and canine models deficient in
either FVIII or FIX closely resemble the human conditions
5 , and are thus suitable models to study gene
therapy applications.
Since haemophilia A and B are life-long diseases,
gene therapy protocols aimed at treating haemophilia
should consider the long-term potential of each
protocol, and/or the possibility for regular re-administration
of the treatment. A number of gene therapy
approaches have been proposed for haemophi-