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Inherited Eye Disease

Michel MichaelidesMoorfields Eye Hospital &

UCL Institute of Ophthalmology

Single gene disorders affecting the retina

Inherited retinal dystrophies• clinically heterogeneous• variable visual loss • bilateral symmetrical retinal

abnormalities• AD, AR, XL & mitochondrial

inheritance • considerable heterogeneity even

within these subtypes

Inherited retinal dystrophies• phenotypically variable

•onset•rate of progression•severity• fundus appearance•fundus autofluorescence•electrophysiology•psychophysics

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Inherited retinal diseases

• stationary versus progressive• predominant rod vs. cone• macular vs. periphery• structural developmental disorders

Disorders• Retinitis Pigmentosa *

– progressive rod photoreceptor demise• Cone dystrophy / Cone-Rod dystrophy• Achromatopsia *

– Stationary cone dysfunction• Congenital night blindness *

– Stationary rod dysfunction• Macular Dystrophies

– Best Disease

a-wave

a-wave

b-wave

b-wave

PERG

P50

N95

EOG

ERG

PERG

Electrophysiology and retinal structure

Standard full-field ERGs

No significant contribution from the macula

Dark-adapted Light-adapted

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Pattern Electroretinography

contrast response

reflects macularfunction

no significant contribution fromthe peripheral retina

P50

N95

Inheritance• Autosomal dominant• Autosomal recessive• X-linked recessive• Mitochondrial (16,569bp)

• X-linked dominant (incontinentia pigmenti, Aicardi)• Digenic (bi- or triallelic)

– RDS +/- & ROM1 +/- -> RP (Kajiwara, Dryja Science 1994) – Bardet-Biedl Syndrome (Katsanis Science 2001)

• Rules– If male to male not X-linked– If male to anyone not mitochondrial

Number of single gene disorders affecting retinal function

http://www.retnet.org

• 46 year old male• Night blindness since teens• Mainstream education• Driving until 20s• Progressive loss of field• Family history of vision loss (mother,

maternal uncle, maternal grand-father)

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Autosomal Dominant RP

• Rhodopsin gene (RP4) chromosome 3q• Mutation

– c.1040c->t– p.Pro347Leu

Rod opsin – 25000 /µm membrane, 108 / outer segment

• Night-blindness• Fit and well, no medication history

• Acuities 6/6 6/6 (emmetrope)• Mild restriction of visual field

14 year old boy

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IV:8

III:6III:5

IV:9 IV:10

II:3 II:4

III:2 III:4III:3

IV:6 IV:7

III:1

IV:1 IV:5IV:4IV:3

V:2

IV:2

V:1

II:5 II:6

I:1 I:2

II:1 II:2

14 YRS

glaucoma

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IV:10

III:8III:7

IV:11 IV:12

II:4 II:5

III:4 III:6III:5

IV:8 IV:9

III:3

IV:3 IV:7IV:6IV:5

V:3

IV:4

V:2

II:6 II:7

I:1 I:2

II:2 II:3II:1

III:2III:1

IV:2IV:1

V:1

14 YRS

IVS 6 + 3 A>G

Exon 6

Splicing factor PRPF31

RP11• 19q ADRP Vithana et al. (2001) PRPF31• one of four splicing genes causative of

ADRP –– PRPF8 – RP13, 17p– PRPF3 – RP18, 1q– Pim-1 kinase Activating protein – RP9, 7p

• non-penetrance of carriers is due to allele from non-affected parent.

ADRP genes• rod opsin - RP4 - 3q• NRL - RP27 14q ＃• PRPF8 - RP13 - 17p• PRPF31 - RP11 - 19q *• PRPF3 - RP18 - 1q• PAP1 - RP9 - 7p *• IMPDH1 - RP10 - 7q • NR2E3 – 15q ＃• RDH12 – 14q ＃• TOPORS – RP31 – 9q• RDS - RP7 - 6p • ORP1 - RP1 8q *

Red – rod specific expressionBlue – splicing factorDark blue – other ubiquitously expressed geneGreen – expressed in both rods and cones, rods more susceptible to mutation＃ - other alleles cause recessive disease

http://www.retnet.org

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Non-syndromic ARRP genes

– USH2A– NR2E3– PDE6A– PDE6B– LRAT– MERTK – central macular hyperfluorescent plaque– CNGA1– CNGB1– CERKL– RLBP1 – white dots when early, gyrate-like appearance later– RGR– RDH12– SAG– TULP1– AIPL1– CRB1 – perivascular sparing, retinal thickening and RPE pigment– GUCY2D - severe, photophobia common, preserved retinal appearance– RPE65 - absent retinal autofluorescence– RPGRIP1– ABCA4 - starts with macular dystrophy– CYP4V2 - intraretinal crystals– NRL – similar to NR2E3 disease– SPATA7– CEP290– LCA5– EYS– IDH3B– PCDH21

♀ 32 yDifficulty seeing detail– Better seeing in the dark (?better than

others)– colour discrimination poor– wears tinted spectacles– ‘no worse’ over lifetime

• No family history, parents are first cousins• VA: BE: 6/60, nystagmus, HRR/Ishihara test

plates only

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RE

LE

N

55586

dark -adapted light -adapted Molecular Genetics

CNGA3 (2q11) : cone -subunit of the cGMP-gated (CNG) cation channel

CNGB3 (8q21-q22) : cone -subunit of the CNG cation channel

GNAT2 (1p13) : cone -subunit of transducin

Chromosome 14 (isodisomy) CNGB3

PDE6C (10q24) : cone -subunit of cGMP-phosphodiesterase (PDE)

Inherited macular dystrophies• progressive central visual loss• clinically heterogeneous• variable severity• bilateral symmetrical macular

abnormalities• AD, AR, XL & mitochondrial

inheritance • dysfunction not always limited to

macula

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Stargardt disease• AR retinal dystrophy• macular atrophy• white flecks at level of RPE• abnormal autofluorescent material

in RPE• lipofuscin accumulation in RPE• abnormal pattern ERG• normal / cone / cone-rod

ffERG

Stargardt disease

Age 14

VA 6/60 6/36

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10 year brother

VA 6/18 6/18

AF imaging in STGD disease

ABCA4 gene• Locus 1p21• 50 exons• highly polymorphic• expressed in rod and cone

photoreceptors• encodes ABC transporter protein

involved in removing all-trans retinal from OS discs

Allikmets et al Nat Genet 1997;17:8269-81

ABCA4 mutations and retinal disease

nullnull

null

normal

RP/CORD

STGD

STGD null

ENVIRONMENT

AMDmissense

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A2E formation in RPE

Sparrow, Janet R. (2003) Proc. Natl. Acad. Sci. USA 100, 4353-4354

A2E is major fluorophore of lipofuscin

Stargardt disease

Associated with accumulation of A2E in RPE

High levels of A2E :-damages cell membranesaffects lysosomal functionresults in release of pro-apoptotic proteins from mitochondria

Sparrow, Janet R. (2003) Proc. Natl. Acad. Sci. USA 100, 4353-4354

Therapy in mouse modelSlow visual cycle:limit light exposureisotretinoin (13-cis retinoic acid)

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Travis et al. (2007) Annu. Rev. Pharmacol. Toxicol. 47, 469-512

Fenretinide

Stargardt disease• primary abnormality is in photoreceptors

• defective ATP dependent transport mechanism

• leads to accumulation of A2E and lipofuscin in RPE

• secondary photoreceptor atrophy

Therapeutic agents may be targeted at the ATP dependent transport mechanism, slowing visual cycle or A2E formation

Subject OS• age 5• nyctalopia from birth• Light staring from 2/52• Squint at 6/12• Poor vision noted from 10/12• Decreased VF from 1 yr• No nystagmus

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Lancelot: 2001

Acland G. M et al., 2001. Gene therapy restores vision in a canine model of childhood blindness. Nat Genet 28, 92-95.

RPE65… is a candidate for gene

therapy

Gene therapy in patients with RPE65 mutations 2008

Maguire et al – NEJM May 2008Bainbridge et al - NEJM May 2008Cideciyan et al – PNAS Sept 2008

RPE65 trials – comparisons

• Subjective improvement in dark vision, 1 – 2 weeks, in two studies

• Improved visual function in 7/9 patients.• ERG, retinal structure (AF OCT)

unchanged• One significant complication – macular

hole (Maguire et al)

Visually-guided mobility: Subject #3; 6 months following surgery

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Gene therapy future• RPE65

– Longer follow up– Younger patients

• RPE disease– MERTK, BEST1, REP1, LRAT, CYP4V2,

RLBP1• Photoreceptor disease• Dominant disease (knock-down replacement

strategy)• Assessing efficacy in a timely fashion is a

significant challenge

Inherited Retinal Dystrophies• wide heterogeneity

• therapy may be possible in progressive disorders

• novel therapies will be directed at patients with known genotype

• knowledge of disease mechanisms will dictate therapeutic approaches

• disorders must be well characterised

• natural history must be known