Transcript Genetic characterisation of PHARC

PHARC – en ny sykdom med ny
sykdomsmekanisme
Laurence Bindoff
Eikholt – Fagkonferanse August 2011
Oversikt

Bakgrunn
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
PHARC syndrom



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Egen
For studiet
Kliniske funn
Utredning
Jakt etter genet
Sykdomsmekanisme
Personal background


Neurologist
Clinical & research
interests



mitochondrial disease
other inherited
neurological diseases
Mitochondrial Medicine
& Neurogenetics
(MMN) group
Studying genetic disease in
Norway
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Geographical
factors
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Natural barriers
to movement
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Dark nights
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Large families?
Concentrated gene pool
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Plague (1349)
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(from England?)
30 - 70 %
population lost
Famine 1800’s
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(English blockade)
Good records
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Genealogical records back to 1500’s
Helge Boman
Limited time!
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Norwegians decide
to move to towns
Norwegians have
found the
Mediterranean

(again)
Background for PHARC
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PHARC ascertained
as “Refsum’s like”
Refsum’s Disease
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Demyelinating
neuropathy; ataxia &
retinitis pigmentosa
Also cataract,
anosmia, deafness,
icthyosis, skeletal
abnormalities, cardiac
involvement
PHARC - Family 1
Patient V:1
Patient V:2
Patient V:4
Early cataract
+
+
+
Sensorineural hearing loss
+
+
+
Sensory & motor neuropathy
+
+
+
Ataxia
+
++
+(+)
Hyperreflexia
−
+
−
Extensor plantar response
−
+
+
Tapetoretinal disease
+
+
(+)
Optic atrophy
+
−
−
Tremor (intention)
−
+
+
(+)
+
−
Anosmia
−
NT
NT
Skin involvement
−
−
−
Cerebellar dysarthria
Summary
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Patients present with:
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visual problems

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hearing impairment
gait disturbance develops late
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either cataract or retinal disease
combination of peripheral & central dysfunction
Neurological impairment
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Peripheral neuropathy is present early but
symptoms develop late!
both pyramidal and cerebellar disease
PHARC - acronym
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Peripheral
neuropathy
Hearing loss
Ataxia & pyramidal
tract (not all)
Retinal
pigmentation
Cataract
PHARC - Investigations
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Normal:
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phytanic &
pristanic acid
VLCFA
peroxisomal
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β-oxidation
α- oxidation
vitamin E
PHARC - Investigations
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Normal:
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Metabolic
screening
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inc. lactate
Muscle biopsy
Various gene tests
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SCA7
Frataxin
mtDNA

ATPase 6
So far:
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Found a new disease
But, no evidence of
which biochemical
pathway involved
Question
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How to find the
cause?
PHARC - Linkage
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Assumptions
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Autosomal recessive
disorder
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Parents distantly
related
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Common ancestral
couple linking the 2
sibs to affected third
cousin occurred 6-7
generations back.
Identity by descent
Patient homozygous for
deleterious mutation
Used homozygosity
mapping (2007)
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400 microsatellite
markers
Locus
20p11.21-q12
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LOD score 6.3
~16Mb (12 cM)
>130 genes
Sequenced 21
Did not give up!
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Found further 5 families
with similar disease
Used 250K SNP chip
Reduced region from 16 to
ca. 6 Mb
 ~60 genes
 sequenced 23
Homozygous indel mutation
in exon 3 in the ABHD12
gene (c.337_338delGAinsTTT)
Enter the rest of the world
Mutations in ABHD12
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Norwegian - frameshift leads to a premature stop codon
(p.Asp113PhefsX15).
Emirates - 14 Kb deletion of promoter region and exon 1
Algerian - 7 bp duplication in exon 9 (p.His285fsX1).
USA - nonsense mutation (c.1054C>T) in exon 12
All mutations considered NULL
19 patients from 3 continents
Finding
Yes
No ?
Age
Comment
S/M
neuropathy
19
-
-
?from
birth
demyelinating
100%
Pes cavus
19
-
-
early
= Neuropathy
Deafness
16
2
1
teens
range 6->30
Cataract
16
3
-
teens/20
range 15->40
Retinal disease
12
3
4
>20
late phenomenon
Ataxia (sensory 14
> central)
4
1
2->40
earlier M. East
families
Pyramidal tract
14
2
3
late
mild - moderate
MRI cerebellar
atrophy
11
5
3
3 – late
mild - both vermis
& hemispheres
Summary PHARC
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A clinically distinct syndrome
Caused by mutations in ABHD12
World-wide distribution
First neurodegenerative disorder
linked to endocannabinoid
metabolism
ABHD12
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Codes for an α,β hydrolase (ABHD)
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Currently 17 ABHD known, but function not known for all
Only known disease associated with ABHD5
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Chinarin Dorfman (fat storage disorder)
ABHD12 - only known substrate is endocannabinoid 2arachidonoyl glycerol (2-AG)
Not the only enzyme involved in 2-AG degradation
What do endocannabinoids
do?
CB1 & CB2 are G-protein coupled receptors
i.e. involved in signalling
Where is ABDH12 found in
the cell?
Where is ABDH12
expressed?
ABDH12 and microglia?
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CB2-receptors
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Immune modifying effect
Over-expressed in some neurodegenerative
diseases
Do endocannabinoids modulate function of
microglia & glial cells?
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Migration, activation
Phagocytosis
Secretion of cytokines
Further work
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Antibodies to
ABHD12
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confirm localisation
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Urine, blood,
macrophages
Study metabolites of
2-AG etc
Animal model?
Study PHARC-like
disorders

other defects in
endocannabinoid
related disorders?
Thank you for your
attention!
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Bergen Collaborators
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Genetics
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
Neurology
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T. Fiskerstrand; P.
Knappskog; H Boman;
S. Johansson; B.I.
Haukanes; V.M. Steen
C. Vedeler
Ophthalmology

C. Bredrup
Mutasjon i ABHD12-genet!