Transcript The Genetics of Alternating Hemiplegia of Childhood A long

The Genetics of Alternating
Hemiplegia of Childhood
A long and winding road
Matthew T. Sweney, MD MS
Clinical Instructor, University of Utah
AHC Family Meeting
7/22/11
Overview
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Introduction to AHC
Significant Familial cases
Early investigation
Comparative Genomic Hybridization
Whole Genome Sequencing
Introduction
 Initial Characterization
 Verret & Steele 1971
 8 cases linked by hemiparesis and headache
 Migraine variant
 Disease evolution
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Estimated 1-2 affected children per 1 million
Eye movements, focal dystonia
Hemiparesis/plegia, ataxia
Developmental impact
Diagnostic Criteria
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Onset of symptoms prior to 18 months of age
Repeated attacks of hemiplegia involving either side of the
body
Other paroxysmal disturbances, including tonic or dystonic
spells, oculomotor abnormalities and autonomic phenomena,
during hemiplegic bouts or in isolation
Episodes of bilateral hemiplegia or quadriplegia as
generalization of a hemiplegic episode or bilateral from the
beginning
Immediate disappearance of symptoms upon sleeping, which
later may resume after waking
Evidence of developmental delay and neurologic
abnormalities including choreoathetosis, dystonia, or ataxia
Introduction
 Diagnostic challenge
 Relationship to known paroxysmal diseases
 Familial Hemiplegic Migraine
 Episodic Ataxias
 Periodic Paralysis
 Relationship to epilepsy
 Typical events not epileptic
 Suspected epileptic events in ~50% of cases
 As yet unknown pathophysiology
 Suspected channelopathy
University of Utah AHC database
 Affected individuals referred by Physicians,
Family Support Organizations
 Clinical data and DNA/cell line collection
via IRB approved protocol since 1999
 Contact with patients by phone/written
communication/in-person at regional
meetings
University of Utah AHC database
 Pediatrics, March 2009
 172 patients consented to enrollment
 103 patients met diagnostic criteria
 Largest database of AHC patients in the world
 Familial cases
 5 kindreds with multiple children affected
 Others reported, however inadequate medical records or
no blood specimen available
Familial Cases
Translocation
T(3;9)(p14.3;q34.3)
BAC 370G13 Contig
human tear
prealbumin
cos3-T7
5.9 kb
AA683210
hNT neuron
R52874 KIAA0649 F11681
U46429 (brain) (infant brain) cpG island
BAC-T7 BAC-sp6
cos3-T7
24 kb
22.4 kb
KIAA0649
cos27-T3
8.4 kb
cos3-T3 cos55-T7
LCN1c
Total length largest contig 83 kb
cos55 37 kb
26.5 kb fragment with
germ cell cDNA AI662518
AA778411
(fetal heart)
cos55-T3 Odorant
binding protein
Candidate Genes
 Translocation breakpoint
 MRPS2, mitochondrial ribosomal protein
 KIAA1422 (KCNT1), calcium activated K+
channel, near translocation breakpoint 9q
 KIAA0649--Function unknown
 Looks promising, right?…
Unaffected Carriers
Gene Candidates
 CACNA1A, Calcium channel associated with FHM,
19p13.2--bridge phenotypes?
 ATP1A2, Positive lod score and shared haplotype for
K7940; mutations in two families associated with FHM2
phenotype
 SCN1A, mutations found in 3 families with familial
hemiplegic migraine (FHM3)
 SLC1A3-EAAT1, Glutamate transporter. Joana Jen
identified a point mutation in one sporadic affected
individual.
More Genes
 CACNA1D, Brain expressed calcium channel,
near translocation breakpoint 3p
 SLC6A11, Distal 3p near breakpoint
 ATP2B2, Near breakpoint in K4323
 CACNA1I, Calcium channel, Positive lod in
K4323
 In all, from 1999 to 2008, 25 candidate
genes screened
Comparative Genomic Hybridization
 AKA Microarray
Analysis
 Assesses copy number
changes in DNA
content
 Uses 244,000 known
probes
 Covers genes and noncoding regions
CGH
 10 subjects in small pilot trial
 All met classic criteria
 Numerous single-probe copy number
variations shared across all 10
 No contiguous probe deletion or duplication
shared by all subjects
 No clear answers revealed
Current work
 AHC: Pepsi Refresh Grant
 $250,000 grant awarded for the purposes of
identifying the genetic cause of AHC
 23 samples sent for whole genome sequencing
 Sent via ISB to Complete Genomics, Inc
 Provides sequenced data and variant reports
 Preliminary data in August, 2011, complete
analysis may take additional 6-12 months
Why is this important?
 Sequencing represents the standard by
which other modes are judged
 Finally the cost of sequencing is practical
 The service we use provide both genetic
sequencing as well as preliminary statistical
analysis
 Data will hopefully serve as foundation for
therapy or cure
Where do we go from here?
 Wait for sequencing to be completed
 Statistical analysis of the sequencing
 Identify if it is one gene or combination of
genes
 Identify the function of those gene(s) and
model them
 Once the function is delineated, identify
ways to modify/improve it
Conclusions
 Complicated, rare disease
 Highlights the rationally haphazard
approach in a gene hunt
 Exemplifies the challenges present with
under-recognized disease, underfunded
research, understaffed workforce
 Presents great opportunity to make an
impact
Acknowledgments
 Kathryn J. Swoboda, MD
 Pediatric Motor Disorders Group: Sandy
Reyna, MD, Aga Lewelt, MD, Abby Smart, RN
 Fran Filloux, MD, Stefan Pulst, MD, Art
Brothman, PhD
 Alternating Hemiplegia of Childhood
Foundation