Transcript RETT SYNDROME

RETT SYNDROME
UNDERSTANDING RETT
SYNDROME AND THE ROLE OF
MECP2
NEUROSCIENCE
JANUARY 2009
OUTLINE
CLINICAL BACKGROUND
MOLECULAR IMPLICATIONS
PHENOTYPE-GENOTYPE RELATION
ANIMAL MODELS
THERAPY
Rett syndrome is caused by mutations in X-linked
MECP2, encoding methyl-CpG-binding protein 2
Ruthie E. Amir, Ignatia B. van den
Veyver, Mimi Wan, Charles Q. Tran, Uta
Francke & Huda Y. Zoghbi Nature
Genet 1999;23:185
RETT SYNDROME
A NEURODEVELOPMENTAL DISORDER OF
YOUNG FEMALES CHARACTERIZED BY
 PROFOUND COGNITIVE
IMPAIRMENT
 COMMUNICATION DYSFUNCTION
 STEREOTYPIC MOVEMENTS
 PERVASIVE GROWTH FAILURE
RETT SYNDROME
CONSENSUS CRITERIA - 2001







Normal at birth
Apparently normal early development (may be
delayed from birth)
Postnatal deceleration of head growth in most
Lack of achieved purposeful hand skills
Psychomotor regression: Emerging social
withdrawal, communication dysfunction, loss
of learned words, and cognitive impairment
Stereotypic movements: Hand
washing/wringing/squeezing; Hand
clapping/tapping/rubbing; Hand mouthing
Gait dysfunction: Impaired (dyspraxic) or
failing locomotion
RETT SYNDROME
TEMPORAL PROFILE
 APPARENTLY NORMAL DEVELOPMENT
 ARREST OF DEVELOPMENTAL
PROGRESS
 FRANK REGRESSION WITH POOR
SOCIAL CONTACT AND FINGER
SKILLS
 STABILIZATION: BETTER SOCIAL
CONTACT AND EYE GAZE, BUT
GRADUAL SLOWING OF MOTOR
FUNCTIONS
RETT SYNDROME
What do we know?
 Genetic disorder - mainly in females
 Diagnosis based on meeting clinical
criteria
 Variable clinical expression
 Significant longevity
 Consistent neuropathology
RETT SYNDROME
BRAIN MORPHOLOGY
 REDUCED BRAIN WEIGHT
 REDUCED VOLUME OF SPECIFIC REGIONS
 REDUCED MELANIN PIGMENTATION
 SMALL NEURONS; SIMPLIFIED DENDRITES
WITH REDUCED SPINES
 ABSENCE OF RECOGNIZABLE DISEASE
Spine Dysgenesis in Mental Retardation
Normal
DS
MR
FraX
FMR1 KO mice
wt
Rett Syndrome
• Down’s Syndrome (Huttenlocher ‘70, ‘74; Marin-Padilla ‘72, ‘76; Purpura ‘74, ‘75); Fragile X Syndrome - and
FMR1 KO mice (Wisniewski ‘85; Greenough ‘97); Rett Syndrome (Balichenko ‘94)
OTHER NEURODEVELOPMENTAL
DISORDERS

DOWN SYNDROME
 REDUCED DENDRITIC BRANCHES AND SPINES
AFTER EARLY INFANCY

AUTISM
 INCREASED PACKING DENSITY
 DECREASED CELL SIZE

ANGELMAN AND FRAGILE X SYNDROMES:
 REDUCED DENDRITIC ARBORIZATIONS AND
SPINES





RETT SYNDROME AND MECP2
RETT SYNDROME IS A CLINICAL DIAGNOSIS
RETT SYNDROME IS NOT SYNONYMOUS
WITH MECP2 MUTATIONS
RETT SYNDROME MAY BE SEEN WITH MECP2
MUTATIONS
RETT SYNDROME MAY BE SEEN WITHOUT
MECP2 MUTATIONS
MECP2 MUTATIONS MAY BE SEEN WITHOUT
RETT SYNDROME
MECP2 AND RETT SYNDROME
 90-95% of classic RTT due to mutations in




MECP2
4 missense and 4 nonsense mutations
account for ~ 65%; c-terminal truncations
and large deletions account for another 1518%
Sporadic RTT: majority of paternal origin
Familial RTT (<<1% of total): majority due
to large deletions
Phenotypes extend beyond classic RTT
Females
Continuum of MECP2
Associated Phenotypes
Males
Normal*
Learning Disabilities*
Behavioral Phenotype*
Autistic; OCD
Hyperactive/aggressive
Moderate cognitive delay
Forme fruste
Preserved speech variant
MECP2 Duplication syndrome*
+/- recurrent infections
X-linked cognitive impairment*
+/- progressive spasticity;
other NDD features/OCD;
aggression
Rett syndrome
95% with MECP2
mutation; 80-85% of RTT
and variants
Rett syndrome
XXY; somatic mosaicism
Early onset seizure variant
Severe encephalopathy*
Congenital variant
*
*Likely under-represented
Medical Issues
Longevity
Growth
Epilepsy
GI dysfunction
Scoliosis
Osteopenia
Breathing irregularities
Sleep
Cardiac conduction
Sexual Maturation
LONGEVITY IN RETT
SYNDROME
 Unpublished study from Baylor College of
Medicine: survival follows that of all
females until age 10; 70% survival to age
35 versus 98% in all females
 Recent study from Australia: 78% survival
to age 25 versus 99.9% in all females Laurvick et al. J Pediatr 2006;148:347
RETT SYNDROME – SURVIVAL BY DATE OF
BIRTH
Figure 1
1. 00
0. 75
0. 50
0. 25
0. 00
0
10
20
30
40
50
Y E A RS
S T RA T A :
B Y E A R= 1 9 3 5 - 1 9 5 9
B Y E A R= 1 9 8 0 - 1 9 8 9
B Y E A R= 1 9 6 0 - 1 9 6 9
B Y E A R= 1 9 9 0 - 1 9 9 9
B Y E A R= 1 9 7 0 - 1 9 7 9
B Y E A R= 2 0 0 0 - 2 0 0 9
60
70
MOLECULAR IMPLICATIONS
METHYL-CpG-BINDING PROTEIN 2
 ONE OF FAMILY OF METHYL-BINDING
PROTEINS
 CAPABLE OF TRANSCRIPTIONAL
SILENCING OR REGULATION
 UBIQUITOUS IN MAMMALIAN
TISSUES
 HIGHLY EXPRESSED IN MAMMALIAN
BRAIN
 SPECIFIC TARGET GENES UNDEFINED
 MAY FUNCTION IN MAINTENANCE OF
DEVELOPING AND MATURE NEURONS
MeCP2 DISTRIBUTION IN HUMAN
BRAIN DURING DEVELOPMENT
 CAUDAL-ROSTRAL GRADIENT OF MeCP2 IN HUMAN

BRAIN
CORTICAL NEURONS LAST TO EXPRESS
Shahbazian et al. Hum Mol Genet 2002;11:115
Mecp2 plays complex role in the nucleus
with differential effects on transcription
Yasui et al. PNAS 2007
Chahrour et al. Science 2008
Mutated MeCP2
HDAC
Sin3A
MeCP2
Methylated
CpG
Chromatin
PHENOTYPE-GENOTYPE
RELATION
Does mutation predict
outcome
R133C, R294X, and R306C mutations
and c-term truncations are
associated with lower severity
scores, slower progression,
preserved speech
Classic RTT: missense and nonsense
Variant RTT: nonsense
Non-RTT: missense and frameshift
Medical Issues
Frequency (%) by Mutation Type
Mutation (n)
Seizures
Scoliosis
Sc Surgery
R106W (20)
78
45
15
R133C
(28)
50
25
0
T158M
(64)
74
50
16
R168X
(55)
54
35
11
R255X
(60)
49
42
7
R270X
(34)
53
50
12
R294X
(37)
69
43
3
R306C
(45)
49
31
4
Lrg del (49)
57
55
12
c-ter del (53)
69
51
9
Medical Issues
Frequency (%) by Mutation Type
Mutation (n)
R106W (20)
Constipation
75
GERD
50
Fractures
20
R133C (28)
T158M (64)
R168X (55)
75
78
73
43
56
55
7
16
16
R255X
R270X
R294X
(60)
(34)
(37)
75
74
81
52
62
49
17
27
19
R306C (45)
Lrg del (49)
c-ter del (53)
62
69
75
47
55
38
13
20
13
MOUSE MODELS
Knock-out mouse: Mecp2 deleted
Knock-in mouse: Insertion of
mutation in Mecp2
KNOCK-OUT MUTANT
Is Mecp2 knock-out reversible?
Using estrogen receptor
controlled Mecp2 promoter:
– Mecp2 knock-out phenotype
reversed in both immature male
and mature male and female mice
with estrogen analog, tamoxifen
– Rapid re-expression in immature
males resulted in death in 50%
Guy et al. Science 2007;315:1143-1147
KNOCK-IN MUTANT
Note
humped
back and
forelimb
clasping
Young and
Zoghbi, Am J
Hum Genet
2004;74:511520
KNOCK-IN MUTANT
Impaired hippocampusdependent social, spatial, and
contextual fear memory
Impaired long-term potentiation
and depression
Reduced post-synaptic densities
No change in BDNF expression
327
Moretti et al. J Neurosci 2006;26:319-
KNOCK-IN MUTANT
Enhanced anxiety and fear based
on:
– Elevated blood corticosterone levels
– Elevated corticotropin-releasing
hormone in hypothalamus, central
nucleus of amygdala, and bed
nucleus of stria terminalis
– MeCP2 binds to Crh promoter
methylated region
McGill et al. PNAS 2006;103:18267-18272
KNOCK-IN MUTANT
Implications of Crh overexpression:
– Anxiety plays central role in clinical
RS
– Amygdala has direct input into
hypothalamus and brainstem
autonomic nuclei correlating with
clinical problems of respiration, GI
function, and peripheral
sympathetic NS
– Suggests strategies for therapeutic
intervention
But overexpression is
detrimental
Collins et al., HMG 2004
THERAPY
Therapeutic interventions in
Rett syndrome
Genetic
Gene therapy
Post-transcriptional
repair
Protein
Reintroduce
protein
Modifiers of mutant
MECP2 function
http://fajerpc.magnet.fsu.edu/Education/2010/
New treatments on the horizon?
Gene repair, replacement strategies
 Gene therapy
 Reintroduction of protein
Can we modulate expression of the gene/protein?
 Up-regulation in “normal” cells in heterozygotes
 Reactivate normal gene
Post transcriptional repair
 Treatment being tested in CF and Duchenne muscular
dystrophy of a drug that allows the cell to “read through” a
nonsense mutation
Targeted treatments based on what Mecp2 does in neurons
 Can we improve protein function?
 Can we make another protein take over?
Can we intercede on specific downstream targets?
Can we modulate neurophysiology?
Challenges across the board for
therapies in Rett syndrome
 No clear-cut reliable outcome measure for all
the girls.
 Natural history study may be key.
 ?EEG or other objective physiologic measure.
 Girls will be heterogeneous in genetic
background and XCI.
 Even in cultured cells, outcome measures are
tricky.
 But the mice can help us here…..
What about gene therapy for Rett
syndrome?
Disorders due to mutations in
one or more genes
–Single-gene disorders are
more easily treated
The responsible gene is
known
+/- The role of the protein
encoded by the gene is known
+ Adding a normal gene will fix
the problem
The affected tissues are
known and accessible
Gene therapy
Post-transcriptional repair:
aminoglycosides
Aminoglycoside
antibiotics allow “readthrough” of premature
stop signals
 Nonsense mutations
 Problems with
toxicity
 Need to be given IV
Introduce a missense
mutation at the “stop”
site
http://www.ptcbio.com/3.1.1_genetic_disorders.aspx
Post-transcriptional repair?
PTC124: New Agent
developed by PTC
Therapeutics with
similar action
 Orally available
 Less toxic
 Being tested in cystic
fibrosis and Duchenne
Muscular Dystrophy with
very promising results
 Phase 2 trials- increased
walking duration in DMD,
improved chloride
conductance in CF
http://www.ptcbio.com/3.1.1_genetic_disorders.aspx
Therapies for Rett Syndrome
Nutrition
Physical Therapy
Occupational Therapy
Communication Therapy
Hippotherapy
Music Therapy
Aquatherapy
TOE WALKING
ANKLE-FOOT DYSTONIA
A successful
intervention
Conclusions
Current investigations into neurobiological
underpinnings of CNS dysfunction opening
doors to new therapies in immediate future.
– Repurposing existing drugs
– Development of new agents
Gene based therapies are potential avenues
of treatment in the future.
Role of environmental enrichment (supports
early intervention programs)
Need to examine treatments in female mice
Cogent planning needed for clinical trials for
selected agents
The Team
Baylor College of
Medicine
–
–
–
–
–
Daniel Glaze
Kay Motil
Jeff Neul
Judy Barrish
Carmel Lusk
Greenwood Genetic
Center
–
–
–
–
Steve Skinner
Fran Annese
Joy Graham
Lauren McNair
UAB
–
–
–
–
–
Alan Percy
Jane Lane
Suzie Geerts
Jerry Childers
Russell Kirby
NIH/NCRR/NICHD
DTCC – Hye-Seung Lee
Girls and women with
RS and their families
…Rollin’ with Curly