Notes
From Murdoch Meeting on FA
Dear INTERNAF
participants,
Considering
the high level of interest of the subject, I think an update
on FRDA research and perspectives for treatment was long
overdue. I take the opportunity of the report about the
Melbourne meeting to do that.
First, where
are we with research? In brief, investigations are
continuing at all levels.
At the DNA
level, analysis of the properties and effect on gene
expression of the GAA expansion (I remind that in FRDA there
is a GAA triplet repeat expansion in the first intron of the
frataxin gene) is going on. It is now clear that the
expansion results in a low level of frataxin (from 3-4% to
20-25% of normal), and the mechanisms are actively
investigated in a number of models.
At the
cellular level, it has been established that frataxin is a
mitochondrial protein, expressed at highest levels in the
tissues affected by the disease. Hints about its function
came from experiments in yeast, indicating that in this
organism frataxin prevents iron accumulation in
mitochondria. Yeast cells without frataxin become also very
sensitive to oxidants, and this is because iron reacts with
some oxigen-derived molecules (normally generated in cells
as by-products of respiration) to produce highly reactive
substances (free radicals) that damage cellular structures.
The Fenton reaction, quoted in a message to INTERNAF, is the
reaction of iron with hydrogen peroxide that generates the
highly toxic hydroxyl radical. Some evidence of disturbed
iron metabolism in FRDA patient was already available (e.g.
iron deposits in the heart), and additional evidence was
found recently (deficiency of some iron-containing enzymes
also in the heart). Current research is focusing on
investigating if frataxin deficiency in human cells also
results in mitochondrial iron accumulation and oxidative
damage. Mouse models of FRDA (frataxin deficient mice) are
being developed in at least two labs and will be available
in several months. These mice will make no frataxin at all,
different from the human FRDA patient who still make some
protein, so they may be very severely affected or even not
viable. We have to wait and see. In addition, blood studies
and studies with magnetic resonance imaging and spectroscopy
are planned or being done to detect possible anomalies of
iron metabolism that can be monitored in patients, and
possibly used not only to investigate the disease process,
but also to follow up the effect of any experimental
treatment.
Analysis of
mutations is also continuing, including the rare frataxin
point mutations, that is DNA abnormalities in the coding
sequence for frataxin which cause a deficiency in a
different way than the GAA expansion. Concerning FRDA cases
without any mutation in the frataxin gene, in my experience
(and also reported in published papers) there are rare
individuals with a FRDA-like clinical picture whose disease
is due to abnormalities in a different, yet unidentified
gene on a different chromosome. If there are also cases with
different, yet undetected frataxin mutations remains to be
established.
Concerning
perspectives for treatment trials in the not-so-distant
future, discussion is going on among the participants to the
network created at the Montreal meeting (29 May - 1 June,
1997). In addition, on October 29 some of us had a very
interesting meeting in Baltimore in which many issues
concerning possible drug trials in FRDA were discussed.
Participant, in addition to myself, included Drs. T.
Ashizawa (Baylor Coll. of Med., Houston), D. Geschwind
(UCLA), H. Paulson (Philadelphia), B. Keats (New Orleans),
S. Forrest (representing the Melbourne group), M. Scavina
(Dupont Institute, Wilmington), and two hematologists, one
from the Dupont Institute and one from U. of Utah. There was
a general consensus that any trial with patients should be
postponed until more basic research has been carried out.
The key points are:
a)
Determine to what extent the yeast knock-out data can be
replicated in human FRDA cells, including evidence of
mitochondrial iron accumulation and of increased
sensitivity to oxidants;
b) Collect
evidence of iron accumulation and oxidative damage in
patients pathological samples.
c)
Evaluate if iron chelators are effective in cell culture
to remove excess iron from mitochondria and to correct
any observed defect in FRDA cells;
Inclusion and
exclusion criteria for a trial, possible drug choices,
dosage, and route of administration, evaluation and testing
of patients in trials were also discussed. In summary, if
research results will confirm that this is a promising
avenue, chelator trials may possibly be planned within the
next year.
I have also
to say that some groups would like to go ahead in a shorter
time with trials involving only antioxidant drugs,
considered much safer than chelators. Antioxidants would not
remove any excess iron, but would contrast its
effects.
I
hope this summary helped.
Sincerely,
Massimo
Pandolfo, M.D.
Chercheur Agrege, Departement de Medecine, University de
Montreal
Adjunct Professor, Department of Neurology and Neurosurgery,
McGill University
Centre Hospitalier Universitaire de Montreal
Centre de Recherche Louis-Charles Simard
1560 rue Sherbrooke Est
Montreal, Quebec H2L 4M1
Canada
Phone (+1)
514-281-6000 ext.8928 (office)
(+1)
514-281-6000 ext.8935-6 (lab)
(+1)
514-896-4762 (fax)
email:
massimo.pandolfo@umontreal.ca
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