Retinal Genetics and Prosthetics: Where are we in 2013?

Retinal Genetics and Prosthetics:Where are we in 2013?

VRS Retinal Update 2013D. Wilkin Parke III, M.D.

Objectives

• Describe the clinical value of current genetic testing for AMD

• Describe some currently available retinal prostheses and clinical scenarios in which they might be beneficial

Other subjects in retina have better photos

Scenario 1• You’re on a flight out of town and the

guy next to you recognizes you as his mother’s doctor

• Mom has AMD and son desperately wants to know whether the whole family should get genetic testing

• You blame the ad for an AMD gene test that you see in the in-flight magazine

• Your smart phone is turned off and it’s a three-hour flight

• What do you say?

Genetic testing for AMD

#1: What role do genes play in development of AMD and advanced AMD?

#2: Which genes look like the big players?#3: Can we risk stratify patients yet?– Is this any better than a good exam?

#4: Can we target therapy to genotype?

AMD in the U.S.

2012• 2.2 million with AMD• 300,000 with wet AMD

2020• 3 million with AMD• 400,000 with wet AMD

• Not only is it a leading cause of blindness, but 50% of all new registered blindness!

• 30% greater than 75 will have it

Risk FactorsModifiable:• Smoking• Hypertension• Hyperlipidemia• Obesity• Sunlight exposure

Not modifiable:• Genetics• Age





How important are genes in AMD?

• FH: First degree relative is at 6-12x higher risk than the general population

• Genetic variants are responsible for 60-70% of the risk (Seddon et al 2009, Spencer et al 2011)

AMD Gene Consortium

• Confirmed 12 and identified 6 more loci of AMD “susceptibility” in a meta-analysis of 7600 cases (Holliday et al 2013)

• Asian and European gene markers appear different in prevalence and significance





Genes in AMD

• Complement factor H (CFH)– Chrom 1q31– The first one for AMD, 2005– Alternate complement pathway

• ARMS2/HTRA1– Chrom 10q26– Age-related maculopathy

susceptibility factor 2– Extracellular matrix and basement

membrane formation

Others:• Chromosome 6

• Complement component 2 (C2) and complement factor B (CFB)

• Nearby genes for VEGF-A and Col10A• Chromosome 9

• Nearby genes for Col15A1, TGFBR1, ABCA1

• Weaker associations on chromosomes 2, 3, 4, 5, 8, 12, 15, 17, 18, 21

Rare variants• CFH mutation (CFHR1*B)

associated with hemolytic uremic syndrome, – found in some individuals with

nonsyndromic AMD• PRPH2 gene mutation is

associated with a CACD-like macular atrophy

• ABCA gene polymorphisms have been associated with severe AMD

Rare variants (cont’d)• Elastin mutations identified in

Japanese with AMD– Leads some to think that IPCV may be a

subtype of AMD expressed in certain genetic variations

• Case control studies are not possible with these conditions—they’re too rare

• Distinguishing atypical AMD from other macular diseases can be difficult

Genes to remember

• ARMS2• Chromosome 10

• CFH• Chromosome 1

• What role do genes play in development of AMD and advanced AMD?

• Probably a large one, but there are too many contributing genes and too much environmental modification for us to categorize it as predominantly inherited

• Which genes look like the big players?• CFH and ARMS2 on chromosomes 1 and 10.





Talking about odds ratios• Characteristic 1q31 and 10q26 variants

have the strongest association with development of advanced AMD

• But even for these, odds ratios are difficult to define– Ratios vary based on the study– Different populations– Different phenotypic characteristics– Almost all are case control studies—

not true measurements of relative risk

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Odds ratios for high risk genotypes• CFH (Y402H variant)

– Odds ratio of 2-2.5 in Europeans• ARMS2

– Odds ratio of 6-10 for highest risk genotype• C2/CFB

– Protective alleles may reduce risk by 45-53%• CFH and ARMS2 – highest risk genotypes for both

– Odds ratio of 62

• Smoking – 10-15% current population, – Odds ratio of 2.5-6

• But these are compared to “normal” age-matched controls!• This is not from prospective monitoring of a population as it ages

What we know

• Those with the highest concentration of high risk alleles have a higher risk than those with the lowest concentration of high risk alleles

• Most patients are in the middle ground

• Most authors agree current tests lack “the level of sensitivity and specificity that one would normally demand of a clinical test” (Jakobsdottir et al 2009)

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So how can we assess risk without genetic testing?

Clinical severity scoreIn each eye:• 1 point for presence of large drusen• 1 point for presence of pigment epithelial abnormality

Score 5-yr risk of late stage AMD0 0.5%1 3%2 12%3 25%4 50%

Ferris FL et al. A simplified severity scale for age-related macular degeneration: AREDS Report No. 18. Arch Ophthalmol 2005; 123(11):1570-4.

Clinical severity scoreFurther modification by age, smoking status, family history

www.ohsucasey.com/amdcalculator

Score 5-yr risk of late stage AMD

70-yr-old nonsmoker

70-yr-old smoker

0 0.5% 1 1

1 3% 5 9

2 12% 11 19

3 25% 25 40

4 50% 34 52


Clinical severity score

Score 5-yr risk of late stage AMD

70-yr-old smoker 70-yr-old smoker, high risk CFH and ARMS2 variants

0 0.5% 1 2

1 3% 9 13

2 12% 19 26

3 25% 40 52

4 50% 52 66

Factoring in the CFH and ARMS2 variants changes the score, but not by much


So is this any better than a good exam?

• Probably not, at least right now





The only things to reduce risk

• Stop smoking• Low glycemic index diet• Lutein and zeaxanthin• Vitamin D (only to avoid deficiency)• Beta-carotene, zinc• UV protection

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Vitamins and genotype

• Antioxidants, lutein, zeaxanthin, and zinc might reduce impact of high risk genotypes (Ho et al 2011, Klein et al 2008)

Anti-VEGF therapy and genotype

• One homozygous CFH genotype and one VEGFA gene variant may be predictive of improved response to anti-VEGF (Chen et al 2012, Abedi F et al 2013)

• No consistent evidence yet of association between at-risk alleles on chromosomes 1 and 10 and either positive or negative responders to therapy (Orlin et al 2012)

Alternative Screening

• Home-based monitoring in the near future– iPhone app– Foresee Home device

• Can we tailor the intensity of home screening to genetic risk?

www.digisight.com

www.foreseehome.com

Patient motivation

• Testing early might motivate higher risk individuals to address risk factors more aggressively

• But this could disadvantage lower risk patients. It might produce surprise and disillusionment if they still get advanced AMD

• Genetic testing is rarely straightforward

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Genetic testing:The holy grail

• In the future we may find the risk-benefit balance for each age, clarify the pharmacogenetic associations, and develop specific monitoring and therapy.

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• “Avoid routine genetic testing for genetically complex disorders like age-related macular degeneration and late-onset primary open angle glaucoma until specific treatment or surveillance strategies have been shown in 1 or more published clinical trials to be of benefit to individuals with specific disease-associated genotypes” (Stone et al 2012)

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Scenario 2

• You had a great vacation and you’re on the flight home

• The flight attendant overhears what you do

• Her son has RP and she’s saving up to send him to Italy for a retinal prosthesis

• She’s happy to take your drink order if you’ll only tell her whether the prosthesis is worth it

• Your smart phone is turned off and it’s still a three-hour flight

• What do you say?

Retinal prosthetics

#1: How do they work?#2: What types are available, and when are

these being used right now?#3: With which patients do we have this

discussion?

Retinal prosthetics



discussion?

Retinal prosthetics:The rationale

• Outer retinal disorders

• Postmortem analyses indicate that after total photoreceptor loss in RP, that up to 90% of inner retinal neurons can remain histologically intact.

• The visual pathway downstream to the photoreceptors remains theoretically viable

Retinal prosthetics

• Electronic implants• Non-electronic implants

Retinal prosthetics

• Electronic implants• Non-electronic implants

The parts• Encoder – converts light into

electrical energy (retina’s data)

• Transducer implant– Formulates stimulation pattern– Triggers electrodes – Electrodes fire in close

proximity to target cells (usually ganglion cells)

– Target cells activated by proximal electrical charge Weiland et al, 2011

Retinal prosthetics



discussion?

Camera in glass frame

Wireless transmitter

Extraocular receiver

Epiretinal Prosthesis

Epiretinal implant/electrode array

Humayun, et al (2003)


4x4 platinum electrode array

Humayun, et al (2003)


• Yanai (2007):– Visual performance tested via simple visual tasks:

• Locate and count objects• Differentiate three objects• Determine orientation of a capital L• Differentiate four directions of a moving object

– Performance was significantly better than chance in 83% of the tests

Subretinal Prosthesis

Chow, et al (2004)

Subretinal Prosthesis

• Chow AY, Pollack JS et al (2004): – Silicon-based subretinal microchip• 5000 microelectrode-tipped microphotodiodes

powered by incident light– Implanted subretinally in 6 patients– Subjective visual improvement seen in all patients

Problems and limitations with electronic prostheses

• Power: – Large heat dissipation per electrode – Implants can’t heat tissue more than 1 degree Celsius. – Limits electrode number

• Cochlear implants do well with only 16 electrodes, but vision requires more resolution

• Triggering the appropriate “on” and “off” neurons• The inner retinal layers show some architectural and

functional change with the photoreceptor degeneration, so the downstream system may not be “normal”

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Retinal Prostheses and RP

Trial

No. of Subjects/ Centers Best Result

Optobionics (phases I and II) 30/4

Expanded visual field, improved ETDRS scores

SSMP Argus I 6/1Motion detection, VA 20/250

IMI 7/1 Some form discriminationRetina Implant Subretinal Device 12/1 Letter reading, VA 20/100 SSMP Argus II 30/10 Letter reading, VA 20/125Retina Implant Alpha Study 5/1

Object localization, letter reading

Modified from Weiland, et al, 2011

Collective experience

• Since 2002, published series with retinal prostheses have come out of the US, Italy, France, Germany, the UK, and Japan.

• The first clinically approved Argus II was performed 10/2011 in Italy.

• The Argus II received FDA approval for adult advanced RP on February 13, 2013.

• Over 70 patients with end-stage RP have received one.

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Retinal prosthetics

#1: How do they work?#2: What types are available, and when are these

being used right now?#3: With which patients do we have this

discussion?

Candidates

• After implantation, training and calibration take time and effort

• This requires a very compliant and aware patient

• Surgical complications have been uncommon but routine follow-up is required

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Candidates

• Only patients with history of functional vision loss who are now LP due to photoreceptor degeneration are candidates for prosthetics

• All prosthetics aim to bypass the PR cell and stimulate the bipolar or ganglion cell

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Where are we going

• Increased stimulator resolution (more electrodes, more transducers)

• Smaller units• More complex neural code incorporation• Determination of best location for the

transducer (subretinal, epiretinal, etc.)• Cortical and optic nerve prostheses also in

development, but no current human trials

Retinal prosthetics

• Electronic implants• Non-electronic implants– Cell/tissue transfer– Gene transfer• Optogenetics• Other gene transfer

Retinal tissue implantation

• Fetal retina/RPE implantation– Surgically transplanted

sheets of fetal neural retina and RPE

Retinal tissue implantation

• Radtke (2008):– 10 patients (6 RP, 4 AMD) – Vision 20/200 or worse – 7 patients (3 RP, 4 AMD)

had improved ETDRS visual acuity

– 2 RP patients had decreased vision

– No clinical rejection of implanted tissue

Optogenetics• Fusing optics and genetics• Concept:– Expression of photosensitive

molecules from bacteria or algae in human cells (photoreceptors, ganglion cells, other neurons)

– Host cells are conferred with optical activity (via gene delivery) and can be manipulated by light.

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Optogenetics

• Research into use throughout body, but eye lends itself to optogenetic technology because it is light accessible

• Unlike electronic prostheses, this offers potential to control gain or loss of function, not just stimulation.

Optogenetics:What can we do right now?

• Mostly using a channel rhodopsin (ChR2), a membrane transport ion channel

• Transfection into neural cells via viral vector

• Virus vector, transfected gene, and expressed protein have been shown to be safe

• Light production by the cells is safe (no phototoxicity reported)

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Credit: Viviana Gradinaru, Murtaza Mogri, and Karl Deisseroth, Stanford University via Science Daily

Optogenetics:Current limitations

• Indiscriminate stimulation– Unable to target specific cells or groups of cells– No discrimination between “on” and “off” cell

types• Response intensity is insufficient

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Other gene therapy

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• Retina is an early clinical adapter because small volumes are needed, there is less risk of systemic toxicity, and there is a contralateral control

• Not necessarily just for genetic defects• Turning off unwanted gene expression

(neovascularization, autoimmune processes, etc.)• Inducing expression of therapeutic molecules (anti-VEGF

agents, corticosteroids)

Gene therapy:Vectors

• Adeno-associated virus, lentivirus, and adenovirus have been studied in the eye

• AAV has the best safety record and transduces cells efficiently

• Nonviral vectors being investigated include lipid or nanoparticles

Gene therapy:Delivery

• Currently vitrectomy and subretinal injection to access the photoreceptor layer

• Suprachoroidal catheterization to target RPE or choroid• Vector penetration through the retina may allow for

intravitreal injection.

Gene therapy:Trials

• LCA Trial: Gene transfer with AAV vector is safe

Current trials:• 9 for inherited dystrophies

– Promising early results for Stargardt, Usher, and choroideremia

• 20-30 for AMD

Stem Cell Companies• Advanced Cell Technology (ACT) – RPE cells for dry AMD and

Stargardt• AstraZeneca – diabetic retinopathy• Janssen R&D – RPE cells for AMD• Cell Cure Neurosciences – RPE cells for dry AMD• Mesoblast – VEGF producing cells for wet AMD• Neostem inc – vessel growth for AMD• Neurotech – RPE cells for AMD, Usher, RP• Pfizer – RPE cells for AMD; stem cells for DR, ROP, RP• Stemedica, • Stem Cells Inc

Conclusions• Genetic testing is appropriately an area of active research in AMD• At this time clinical genetic testing for AMD outside of research does not

have a clearly defined role and is not generally recommended• An old fashioned clinical exam and history are remarkably predictive of

risk for advanced AMD

• Electronic retinal prosthetics are currently available for select patients with very poor vision due to outer retinal degenerations

• Several implant designs have achieved remarkable results in previously blind eyes

• Optogenetics = optics + genetics = very newsworthy right now• Gene therapy trials in the posterior segment will continue to proliferate

References• Abedi F et al. Variants in the VEGFA Gene and Treatment Outcome after Anti-VEGF Treatment for Neovascular Age-

related Macular Degeneration. Ophthalmology 2013 Jan;120(1):115-21.• Acland GM, Aguirre GD, Ray J, Zhang Q, Aleman TS, Cideciyan AV, Pearce-Kelling SE, Anand V, Zeng Y, Maguire AM,

Jacobson SG, Hauswirth WW, Bennett J. Gene therapy restores vision in a canine model of childhood blindness. Nat Genetics. 2001; 28: 92-95.

• Ali RR, Reichel MB, De Alwis M, Kanuga N, Kinnon C, Levinsky RJ, Hunt DM, Bhattacharya SS, Thrasher AJ. Adeno-associated virus gene transfer to mouse retina. Hum Gene Ther. 1998;9: 81-86.

• Berson EL, Rosner B, Sandberg MA, Hayes KC, Nicholson BW, Weigel-DiFranco C. A randomized trial of vitamin A and vitamin E supplementation for retinitis pigmentosa. Arch Ophthalmol. Jun 1993;111(6):761-72.

• Chakravarthy U et al. Clinical risk factors for age-related macular degeneration: a systematic review and meta-analysis. BMC Ophthalmol 2010 Dec 13;10:31.

• Chen H et al. Association between variant Y402H in age-related macular degeneration (AMD) susceptibility gene CFH and treatment response of AMD: a meta-analysis. PLoS One 2012;7(8):e42464

• Chow AY, Chow VY, Packo KH, Pollack JS, Peyman GA, Schuchard R. The artificial silicon retina microchip for the treatment of vision loss from retinitis pigmentosa. Arch Ophthalmol. 2004 Apr;122(4):460-9.

• Edwards AO et al. Complement Factor H polymorphism and age-related macular degeneration. Science 2005; 308(2720):421-4.

• Ferris FL et al. A simplified severity scale for age-related macular degeneration: AREDS Report No. 18. Arch Ophthalmol 2005; 123(11):1570-4.

• Fishman GA, Gilbert LD, Fiscella RG, Kimura Ae, Jampol LM. Acetazolamide for treatment of chronic macular edema of chronic macular edema in retinitis pigmentosa. Arch Ophthalmol. Oct 1989;107(10):1445-52.

• Hageman GS et al. Clinical validation of a genetic model to estimate the risk of developing choroidal neovascular age-related macular degeneration. Human Genomics 2011; 5(5):420-40.

• Holliday EG et al. Insights into the genetic architecture of early stage age-related macular degeneration: a genome-wide association study meta-analysis. PLoS One 2013;8(1):e53830

References• Humayun MS, Weiland JD, Fujii GY, Greenberg R, Williamson R, Little J, Mech B, Cimmarusti V, Van Boemel G, Dagnelie G,

de Juan E. Visual perception in a blind subject with a chronic microelectronic retinal prosthesis. Vision Res. 2003 Nov;43(24):2573-81.

• Jakobsdottir J et al. Susceptibility genes for age-related maculopathy on chromosome 10q26. Am J Hum Gen 2005; 77(3):389-407.

• Klein M et al. Risk assessment model for development of advanced age-related macular degeneration. Science 2005; 308(5720):385-9.

• Klein M et al. CFH and LOC387715/ARMS2 genotypes and treatment with antioxidants and zinc for age-related macular degeneration. Ophthalmology 2008; 115(6):1019-25.

• Orlin A et al. Association between high-risk disease loci and response to anti-vascular endothelial growth factor treatment for wet age-related macular degeneration. Retina 2012 Jan;32(1):4-9.

• Phelan JK, Bok D. A brief review of retinitis pigmentosa and the identified retinitis pigmentosa genes. Mol Vis. Jul 2000;6:116-24.

• Radtke ND, Aramant RB, Petry HM, Green PT, Pidwell DJ, Seiler MJ. Vision improvement in retinal degeneration patients by implantation of retina together with retinal pigment epithelium. Am J Ophthalmol. 2008. [Epub Jun].

• Seddon JM et al. Prediction model for prevalence and incidence of advanced age-related macular degeneration based on genetic, demographic, and environmental variables. Invest Ophthalmol Vis Sci 2009;50(5):2044-53.

• Sofat R et al. Complement factor H genetic variant and age-related macular degeneration: effect size, modifiers, and relationship to disease subtype. Int J Epidemiol 2012 Feb; 41(1):250-62.

• Spencer KL et al. Using genetic variation and environmental risk factor data to identify individuals at high risk for age-related macular degeneration. PLoSOne 2011 Mar 24;6(3):e17784.

• Stone EM et al. Recommendations for Genetic Testing of Inherited Eye Diseases: Report of the American Academy of Ophthalmology Task Force on Genetic Testing. Ophthalmology 2012 Nov; 119(11):1408-10.

• Yanai D, Weiland JD, Mahadevappa M, Greenberg RJ, Fine I, Humayun MS. Visual performance using a retinal prosthesis in three subjects with retinitis pigmentosa. Am J Ophthalmol. 2007 May;143(5):820-827.

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Retinal Genetics and Prosthetics: Where are we in 2013?