Transcript Developing a diagnostic service for Stargardt disease – a

Developing a diagnostic service for
Stargardt disease – a feasibility study
Emily Packham
Oxford Regional Molecular Genetics Laboratory
Introduction
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Inherited eye disorders
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Services currently available for some of the
AD and X-linked conditions
Limited services currently for AR conditions
(Asper Ophthalmics offer commercial
genotyping of some genes)
Why?
Significant clinical overlap
 Genetically heterogeneous
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Stargardt disease may be feasible
Stargardt disease
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Autosomal recessive juvenile macular degeneration
Prevalence of 1 in 10,000
Stargardt disease/Fundus
Flavimaculatus (STGD/FF)
Characterised by yellow-white flecks and atrophy
STGD
FF
Symptoms
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Age of onset varies from early childhood
to twenties
Early stages – difficulty reading, watching
TV, missing patches in vision,
photophobia, slow dark adaption
Later stages – always disturbance of
central vision and sometimes: peripheral
disturbance, increasing photophobia or
problems with dark vision
Diagnosis
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Clinical diagnosis
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Sophisticated imaging but dependent on tests
performed, experience and stage of disorder
Late stage shows clinical overlap
Genetic diagnosis
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Support or confirm diagnosis
Provide prognosis information
Aid genetic counselling
Therapeutic intervention
Genetics of Stargardts disease
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ABCA4 (1p13-p22)
50 exons (6819bp ORF)
Highly polymorphic
No mutation hotspots
500+ variants identified
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Most common seen in ~ <10% of patients
Many missense variants
ABCA4 protein (ABCR / Rim)
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ATP-binding cassette (ABC) transporter
superfamily
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Transmembrane proteins involved in
transportation of compounds across cell
membranes
2273 amino acid protein expressed in
cones and rods
ABCA4 function and disease pathology
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Actively ‘flips’ Ret-PE across disc rim
membrane
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Enables retinal signalling to continue
Loss-of-function mutations
Loss of/reduction in ABCA4 function
results in accumulation of toxic lipofuscin
deposits
Destroys retinal pigment epithelium and
rod and cone cells, resulting in visual loss
ABCA4 and other retinopathies
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Stargardt disease
AR cone-rod dystrophy
AR retinitis pigmentosa
Age-related macular degeneration?
Genotype/phenotype correlation model
based on residual activity of protein
Screening strategy
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30 patients selected for testing
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Highly polymorphic, 50 exon gene with
no particular hotspots
Bi-directional sequencing
Robotics approach –5 patients per batch
Pathogenicity investigations performed
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MLPA
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Results
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37 different potential pathogenic variants detected
in 26 patients
No. of variants
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No. of patients
0
4
1
6
2
18
3
2
13/20 patients with two or more variants had all of
them classified as either likely or highly likely
Most common seen in 4 patients
Results
Results
Variant classification
Number detected
Highly likely pathogenic
17
Likely pathogenic
10
Intermediate
10
Total 37
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Extensive published data
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MLPA normal in all 10 patients tested
Feasibility
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Clinical sensitivity
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67% or 43% (+/- intermediate variants)
Higher than literature
 Different screening methods and patient selection
Clinical utility
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Able to interpret most variants
Supports clinical diagnosis, aids counselling and
therapy
Improves equity of access
What next?
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Report our 30 patients
Determine if variants are in trans
Submit gene dossier
Collaborate with BRC retinal research
project
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Evaluating use of high throughput sequencing
to test numerous inherited retinal conditions
NHS lab
BRC
Acknowledgements
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Oxford Molecular Genetics Laboratory
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Oxford Clinical Genetics and BRC
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Anneke Seller
Treena Cranston
Tina Bedenham, Louise Williams, Kate Gibson
Andrea Nemeth
Oxford eye hospital
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Susan Downes