Ophthalmic Genetics, Early Online, 1–4, 2013! Informa Healthcare USA, Inc.

ISSN: 1381-6810 print / 1744-5094 online

DOI: 10.3109/13816810.2013.838273

CASE REPORT

Autosomal-dominant Leber Congenital AmaurosisCaused by a Heterozygous CRX Mutation in a

Father and Son

Karthikeyan Arcot Sadagopan1, Robert Battista2, Rosanne B. Keep1,Jenina E. Capasso1, and Alex V. Levin1,2

1Pediatric Ophthalmology and Ocular Genetics, Wills Eye Institute, Philadelphia, PA, USA and2Thomas Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA, USA

ABSTRACT

Background: Leber congenital amaurosis (LCA) is most often an autosomal recessive disorder. We report a fatherand son with autosomal dominant LCA due to a mutation in the CRX gene.

Materials and Methods: DNA screening using an allele specific assay of 90 of the most common LCA-causingvariations in the coding sequences of AIPL1, CEP290, CRB1, CRX, GUCY2D, RDH12 and RPE65 was performedon the father. Automated DNA sequencing of his son examining exon 3 of the CRX gene was subsequentlyperformed.

Results: Both father and son have a heterozygous single base pair deletion of an adenine at codon 153 in thecoding sequence of the CRX gene resulting in a frameshift mutation.

Conclusion: Mutations involving the CRX gene may demonstrate an autosomal dominant inheritance patternfor LCA.

Keywords: CRX, heterozygous mutation, isoelectric electroretinogram, Leber congenital amaurosis, retinaldystrophy

INTRODUCTION

Leber congenital amaurosis (LCA) is the mostcommon retinal dystrophy in infants. It accounts fornearly 5% of all retinal dystrophies. Features includepoor vision from infancy, nystagmus, oculo-digitalpoking, sluggish pupil response, high hyperopia andan isoelectric electroretinogram. LCA presents with aspectrum of phenotypes and is usually inherited as anautosomal recessive disorder. Mutations in severalgenes have been recognized to cause LCA. Mutationsinvolving the CRX gene have been shown to cause anautosomal dominant form of LCA. Here we report afather and son with autosomal dominant LCA due toa novel mutation in CRX adding further evidence tothis pattern of inheritance.

Case 1

A 3-month-old boy was referred to our OcularGenetics service after presenting to a communityophthalmologist with difficulty in tracking followinga normal birth and delivery. The child’s father (Case 2)was known to have visual compromise. The child’spast medical history was unremarkable.

The patient was found to have central steadymaintained fixation in each eye with no nystagmus.Pupillary responses were normal and no afferentpupillary defect or paradoxical pupil was seen. Eyemovements were full and there was no strabismus.Anterior segment examination was normal. There wasperipapillary hyperpigmentation, slightly small opticnerves, bilateral moderate macular hypoplasia, no

Correspondence: Alex V. Levin, MD, MHSc, Chief, Pediatric Ophthalmology and Ocular Genetics, Wills Eye Institute, 840 Walnut Street,Philadelphia, PA 19107-5109, USA. Tel: +1 215 928 3914. Fax: +1 215 928 3983. E-mail: alevin@willseye.org

Received 29 May 2012; revised 20 August 2013; accepted 20 August 2013; published online 4 October 2013

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abnormal blood vessels or pigmentary clumping, anda generally blond fundus. The cycloplegic refractionwas þ4.00 OU. Electroretinogram was performed inaccordance with the standards for clinical electro-retinography established by the International Societyof Clinical Electrophysiology of Vision (ISCEV). Theelectroretinogram performed under general anesthe-sia using Burian-Allen electrodes showed isoelectricwaveforms to both scotopic and photopic stimuli. Thepatient was seen 2 years later at which time, althoughhe showed preference for fixation with his left eye,visual acuity was light perception. Nystagmus haddeveloped. Anterior segment examination wasnormal. Posterior segment examination disclosedattenuated retinal vessels, optic atrophy, and mid-peripheral pigmentary dropout with some gliosis ofthe macular internal limiting membrane.

Case 2

A 37-year-old male with visual impairment sinceinfancy was seen by us as part of the evaluation of his

son (Case 1). The patient’s visual impairment wor-sened until the age of 14 years at which time he wasunable to ride his bike, and had trouble with otheractivities of daily living. His past medical history wassignificant only for adult onset obesity with hyper-tension and hypercholesterolemia, which are con-trolled with medication. There is no evidence ofparental consanguinity. There are no other affectedfamily members.

Ocular examination showed visual acuity to bebare light perception in each eye. Pupillary responseswere normal and no afferent pupillary defect orparadoxical pupil was seen. The patient had lowfrequency, large amplitude horizontal nystagmuswith some wandering movements. Eye movementswere full although there was a large angle rightexotropia. Anterior segment examination wasnormal. Goldmann applanation eye pressures were20 mmHg in each eye. He had subtle pallor of theoptic nerves, retinal blood vessel attenuation, andmultiple pigmentary clumps in the macula and midperiphery (Figure 1A). The macula was atrophicwith chorioretinal attenuation. Cycloplegic refraction

FIGURE 1. (A) Fundus photograph of Case 2 shows subtle pallor of the disc, moderately attenuated vessels, atrophic macular changesand pigmentary changes. There is increased visibility of the choroidal vessels and absent foveal reflex in both eyes. There are alsoareas of chorioretinal atrophy. (B) Fundus auto-fluorescence of Case 2. There are large areas devoid of auto-fluorescence.The pigmentary changes appear as corresponding areas of reduced auto-fluorescence due to blockage.

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was þ 2.00 Ds OU. An electroretinogram per-formed showed isoelectric wave forms in responseto both scotopic and photopic stimuli in both eyes.Fundus autofluoresence showed severe abnormalities(Figure 1B).

DNA screening using an allele specific assay(The John and Marcia Carver Nonprofit GeneticTesting Laboratory, Iowa city, Iowa, U.S.) of 90 of themost common LCA-causing variations in the codingsequences of AIPL1, CEP290, CRB1, CRX, GUCY2D,RDH12 and RPE65 revealed only one heterozygoussingle base pair deletion of an adenine at codon153 in the coding sequence of the CRX gene resultingin a frameshift (c. 460delA). Automated DNAsequencing of his son specifically examining exon 3of the CRX gene revealed the same mutation. Thegene was then fully sequenced (Casey Eye InstituteMolecular Diagnostics Laboratory, Portland, OR, US.)for both father and son. No other mutationswere found.

DISCUSSION

LCA is a childhood retinal dystrophy characterized byearly severe visual loss and nystagmus with orwithout pigmentary retinopathy.1,2 Visual acuity inchildren with LCA is usually no better than 20/400.3

Electroretinogram recordings typically show minimalor absent responses.2 LCA represents a significantproblem for children, accounting for approximately20% of cases of pediatric blindness and 5% of allretinal dystrophies that affect both children andadults.3–5

LCA is most commonly inherited in an autosomalrecessive fashion but there have been cases repor-ted of autosomal dominant inheritance.1,6 Currentlythere have been 17 genes identified in which muta-tions are associated with the development ofLCA: GUCY2D, CRB1, RPE65, RPGRIP1, AIPL1,LCA5, CRX, LRAT, TULP1, RDH12, CEP290, RD3,SPATA7, IMPDH1, KCNJ17, IQCB1 and NMNAT1.7

Of these genes, mutations in only CRX and IMPDH1have been associated with autosomal dominantLCA.8

CRX belongs to the orthodenticle homeobox (OTX)family of homeobox genes; the three exons of CRXencode a 299 amino acid polypeptide. The CRX geneis a photoreceptor-specific homeodomain transcrip-tion factor that is involved in regulating photoreceptordifferentiation.9 It acts synergistically with the leucinezipper transcription factor, NRL, to maintain theintegrity of the photoreceptors. Mutations in CRXhave been described in autosomal dominant LCA,dominant cone-rod dystrophy and retinitis pigmen-tosa.9–13 Mutations in CRX account for approximately2.35% of LCA cases.14 It has been proposed thatmutations in CRX lead to abnormal photoreceptor

development via altered downstream gene expressionresulting in progressive photoreceptor death.15

This explanation accounts for the progressive visualloss in our patients.

In 2007, Wang and colleagues showed that aheterozygous CRX deletion of cytosine at the secondnucleotide of codon 153 (c.458delC), segregatedwith AD LCA in a three-generation Chinesefamily.7 This deletion caused a frameshift whichresulted in a premature stop codon and led toproduction of a variant protein, p. Pro153GlnfsX34.All six affected individuals had severe visualimpairment with nystagmus since infancy, andabsent pupillary light reflexes. Fundoscopic examrevealed optic atrophy, attenuation of retinal vessels,generalized grayish retinal degeneration and pig-mentary clumps in the periphery and posterior pole.Electroretinogram showed no appreciable rodand cone responses. In 2010, Nichols and col-leagues described two de novo novel mutations inCRX which resulted in a presumed autosomaldominant LCA. One of their patients had a G264Tmutation predicted to change lysine to an aspara-gine in position 88 in the third helix of thehomeodomain. The other had a frameshift mutation(c.413delT) which is predicted to result in shorten-ing of the OTX tail of the protein. The authors showreduced transactivation through functional studies,and postulate an adverse effect of the abnormalproteins on other transcription factors.

Our case report provides further evidence of anautosomal dominant inheritance pattern for LCAand its association with an adenine nucleotidedeletion in codon 153 of the CRX gene. This deletioncauses a frameshift which affects codons 284-295and alters the OTX motif encoded at the carboxylterminus resulting in an abnormal protein(Pro153fsX132). The clinical findings in our casesare similar to the findings in the previous casereported by Wang and colleagues.7 While our casesalso involve codon153, they differ in the specificsequence change, the codon at which the frameshifthas an effect, and hence the protein product.A heterozygous base pair deletion of an A atcodon 153 (Pro153del1ccA) was detected in thecoding sequence of the CRX gene in the father.Automated DNA sequencing of the son alsorevealed the same mutation. The estimated patho-genic probability (EPP Score) of this mutation is 3,which suggests that this mutation is probablydisease causing (The John and Marcia CarverNonprofit Genetic Testing Laboratory, Iowa City,Iowa, USA).

Although dominant LCA is much less commonthan autosomal recessive LCA, our cases demonstratethat dominant LCA must be considered in the work-up and management of patients who present withretinal dystrophy in infancy.

Autosomal-dominant Leber Congenital Amaurosis 3

! 2013 Informa Healthcare USA, Inc.

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DECLARATION OF INTEREST

The authors report no conflicts of interest. The authorsalone are responsible for the content and writing ofthe paper.

Funded in part by the Foerderer Fund (AVL) andthe Alcon Ocular Genetics Fellowship (ASK).

REFERENCES

1. Den Hollander AI, Roepman R, Koenekoop RK, et al. Lebercongenital amaurosis: genes, proteins and disease mech-anisms. Prog Retin Eye Res 2008;27:391–419.

2. Lambert SR, Taylor D, Kriss A. The infant with nystagmus,normal appearing fundi, but an abnormal ERG. SurvOphthalmol 1989;34:173–186.

3. Cremers FP, van den Hurk JA, den Hollander AI.Molecular genetics of Leber congenital amaurosis. HumMol Genet 2002;11:1169–1176.

4. Ahmad A, Daud S, Kakar N, et al. Identification of a novelLCA mutation in a Pakistani family with Leber congenitalamaurosis and cataracts. Mol Vis 2011;17:1940–1945.

5. Li L, Xiao X Li S, et al. Detection of variants in 15 genes in87 unrelated Chinese patients with Leber congenitalamaurosis. PLoS ONE 2011;6:e19458. Accession date 15May 2012. doi:10.1371/journal.pone.0019458.

6. Perrault I, Hannein S, Gerber F, et al. Evidence ofautosomal dominant Leber congenital amaurosis (LCA)underlain by a CRX heterozygous null allele. J Med Genet2003;40:e90 (1–3).

7. Koenekoop RK, Wang H, Majewski J, et al. Mutations inNMNAT1 cause Leber congenital amaurosis and identify anew disease pathway for retinal degeneration. NatureGenet. Published online 29 July 2012; doi:10.1038/ng.2356.

8. Wang P, Guo X, Zhang Q. Further evidence of autosomaldominant Leber congenital amaurosis caused by hetero-zygous CRX mutation. Graefe’s Arch Clin Exp Ophthalmol2007;245:1401–1402.

9. Furukawa T, Morrow EM, Cepko CL. CRX, a novel OTX-like homeobox gene, shows photoreceptor-specific expres-sion and regulates photoreceptor differentiation. Cell 1997;914:531–541.

10. Freund CL, Gregory-Evans CY, Furukawa T, et al. Cone-rod dystrophy due to mutations in a novel photoreceptor-specific homeobox gene (CRX) essential for maintenance ofthe photoreceptor. Cell 1997; 91:543–553.

11. Freund CL, Wang QL, Chen S, et al. De novo mutations inthe CRX homeobox gene associated with Leber congenitalamaurosis. Nat Genet 1998;18:311–312.

12. Sohocki MM, Sullivan LS, Mintz-Hittner HA, et al. A rangeof clinical phenotypes associated with mutations in CRX, aphotoreceptor transcription-factor gene. Am J Hum Genet1998;63:1307–1315.

13. Jacobson SG, Cideciyan AV, Huang Y, et al. Retinaldegeneration with truncation mutations in the cone-rodhomeobox (CRX) gene. Invest Ophthalmol Vis Sci 1998;39:2417–2426.

14. Huang L, Xiao X, Li S, et al. CRX variants in cone–roddystrophy and mutation overview. Biochem Biophys ResComm 2012;426:498–503.

15. Nichols LL, Alur RP, Boobalan E, et al. Two novel CRXmutant proteins causing autosomal dominant Leber con-genital amaurosis interact differently with NRL. HumMutat 2010; 31:e1472–e1483.

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