The Genetics of Alternating Hemiplegia of Childhood A long and winding road

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The Genetics of Alternating Hemiplegia of
ChildhoodA long and winding road

• Matthew T. Sweney, MD MS
• Clinical Instructor, University of Utah
• AHC Family Meeting
• 7/22/11

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Overview 

• Introduction to AHC
• Significant Familial cases
• Early investigation
• Comparative Genomic Hybridization
• Whole Genome Sequencing

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Introduction

• Initial Characterization
• Verret Steele 1971
• 8 cases linked by hemiparesis and headache
• Migraine variant
• Disease evolution
• Estimated 1-2 affected children per 1 million
• Eye movements, focal dystonia
• Hemiparesis/plegia, ataxia
• Developmental impact

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Diagnostic Criteria

1. Onset of symptoms prior to 18 months of age
2. Repeated attacks of hemiplegia involving either
   side of the body
3. Other paroxysmal disturbances, including tonic or
   dystonic spells, oculomotor abnormalities and
   autonomic phenomena, during hemiplegic bouts or
   in isolation
4. Episodes of bilateral hemiplegia or quadriplegia
   as generalization of a hemiplegic episode or
   bilateral from the beginning
5. Immediate disappearance of symptoms upon
   sleeping, which later may resume after waking
6. Evidence of developmental delay and neurologic
   abnormalities including choreoathetosis,
   dystonia, or ataxia

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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

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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

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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

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Familial Cases
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Translocation

• T(39)(p14.3q34.3)

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BAC 370G13 Contig
human tear prealbumin
AA683210 R52874 KIAA0649 F11681
BAC-T7 BAC-sp6 hNT
neuron U46429 (brain) (infant brain)
cpG island cos3-T7

24 kb
22.4 kb
cos3-T7 5.9 kb
KIAA0649
cos27-T3 8.4 kb
cos3-T3 cos55-T7
AA778411 cos55-T3 Odorant

(fetal heart) binding
protein Total length largest contig 83 kb
cos55 37 kb
LCN1c
26.5 kb fragment with germ cell cDNA AI662518
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Candidate Genes

• Translocation breakpoint
• MRPS2, mitochondrial ribosomal protein
• KIAA1422 (KCNT1), calcium activated K channel,
  near translocation breakpoint 9q
• KIAA0649--Function unknown
• Looks promising, right?

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Unaffected Carriers
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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. 

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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

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Comparative Genomic Hybridization

• AKA Microarray Analysis
• Assesses copy number changes in DNA content
• Uses 244,000 known probes
• Covers genes and non-coding regions

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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

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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

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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

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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

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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

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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