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Lessons from the Mouse:
Rett Syndrome is Potentially
Treatable
John Christodoulou
NSW Centre for Rett Syndrome Research
Western Sydney Genetics Program, Children’s Hospital at Westmead
Disciplines of Paediatrics & Child Health and Medical Genetics,
University of Sydney
Testing the motor ability of
Mecp2-deficient mice
Is the brain impairment
in Rett syndrome
permanent?
new research suggests NO!
Reversal of Neurological Defects in a
Mouse Model of Rett Syndrome
Guy et al. Science, 2007
Experimental Design
• created a mouse model where expression of
Mecp2 is blocked
– males have severe neurological abnormalities & reduced
lifespan
– females have less severe neurological abnormalities & normal
survival
• mouse engineered so that Mecp2 expression
is restored on exposure to a specific drug
MECP2 Gene Organisation
MBD TRD
tel
MBD
TRD
3’UTR
3’UTR
cen
Methyl Binding Domain
Transcription Repression Domain
Untranslated Region
Western blot –
absence of
Mecp2 protein
In situ
Survival characteristics
hybridisation
of dentate
typical of null mouse
gyrus
- symptoms develop
@
-no Mecp2
protein
~ 6 weeks & average
survival 11 weeks
The Stop cassette can be cut out of the gene by a
specific enzyme to restore the Mecp2 gene allowing
it to make the normal Mecp2 protein again.
Toxic effect
resembled that seen
when Mecp2 is
overexpressed in
mice.
With reactivation of
Mecp2, 9/17 male RTT
mice developed
toxicity and died.
The rest showed no
toxicity and had
normal survival
Before
12 week old male mouse:
Note low stance, inertia, tremor, arrhythmic breathing, and
moderate hind limb clasping.
Drug treatment was initiated on this day.
After
The same mouse as shown in the previous movie four
weeks later after a course of five weekly drug injections.
Female mice with the Stop cassette develop RTT
features @ 4 – 12 months, have a normal lifespan,
and the phenotype appears to stabilise. Often
become obese.
Female mice that received identical drug treatment regimes 26 weeks prior to filming.
The first mouse seen is a mutant female that displayed symptoms at the beginning of
the treatment and is now indistinguishable from normal.
The second mouse entering the frame is a normal female.
The third mouse to appear is a mutant female not treated. Note inertia and obesity of
this third mouse.
Summary
• absence of MeCP2 does NOT irreversibly
damage brain cells
• there is now real hope that a cure for Rett
syndrome might be possible
• translating this to treatment in humans will
be the next trick!
An Emerging Therapy PTC124
Welch et al. Nature 2007: 447; 87 - 91
Background
• nonsense mutations (in frame UAA, UAG or UGA)
cause the production of the MeCP2 protein to stop
dead
– this is called premature termination
• gentamicin prompts ribosomes to read through
premature termination codons (PTCs)
– but not particularly potent; toxic to the kidneys and inner ear
• small non-toxic compounds identified through high
throughput screening that promote PTC read through
http://www.ptcbio.com/3.1.1_genetic_disorders.aspx
Structural effects of PTC124
on mdx mouse
... and was associated with functional
improvements... PTC124 therapy
results in the
generation of
- improved muscle strength
normal
dystrophin
- reduced exercise associated muscle
damage
protein
- reduced CPK levels (marker of muscle damage)
The Potential for
PTC124 Therapy
• no obvious toxicity
• relatively frequent type of mutation (5 – 70%)
– Duchenne dystrophy
– Rett syndrome
13%
cystic fibrosis
10%
30%
• phase 2 trials in DMD and CF currently under
way