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Novel RPGR Mutations With Distinct Retinitis Pigmentosa Phenotypes in French-Canadian Families ROBERT K. KOENEKOOP, MD, PHD, MAGALI LOYER, MSC, COLLETTE K. HAND, PHD, HUDA AL MAHDI, MD, OLGA DEMBINSKA, PHD, RAQUEL BENEISH, MSC, JULIE RACINE, MSC, AND GUY A. ROULEAU, MD, PHD PURPOSE: To characterize the molecular defects in two x-linked retinitis pigmentosa (RP) families. We hypoth- esized that different RPGR mutations result in distinct RP phenotypes. DESIGN: Observational case series. METHODS: Fifteen members in family I and three members in family II were evaluated. Full ophthalmic evaluations were done. Linkage analyses were performed and likelihood of odds scores (LOD score) were calcu- lated. For mutation analyses, we used dHPLC and auto- mated sequencing. RESULTS: Two novel RPGR mutations were identified in the two families; a Glu 414 (2-bp del) frameshift mutation in family I and an IVS 2–1 (g to a) splice site mutation in family II. All male family members in family I were severely affected by RP but maintained central visual acuities until their 50s and did not develop a bull’s eye maculopathy. The female phenotype was highly variable. Some of the carriers exhibited a severe pheno- type, one female displayed an asymmetric phenotype, and other carriers were asymptomatic. All members with the RPGR frameshift mutation exhibited rod-cone electro- retinograms abnormalities, whereas five members had hearing loss. Male members of family II were severely affected, with early visual acuity loss, central scotomas, and bull’s eye maculopathy. The female family members were asymptomatic but displayed cone-rod electroretino- grams changes. There was no hearing loss. CONCLUSIONS: Different RPGR mutations lead to distinct RP phenotypes, with a highly variable inter- and intrafamilial phenotypic spectrum of disease that is asso- ciated with the type of mutation in RPGR and nonran- dom X chromosome inactivation, respectively. (Am J Ophthalmol 2003;136:678 – 687. © 2003 by Elsevier Inc. All rights reserved.) R ETINITIS PIGMENTOSA (RP) IS A HIGHLY VARIABLE group of diseases characterized by retinal degenera- tion, with progressive night blindness, loss of periph- eral vision, and eventual loss of central vision. Progressive loss of photoreceptor function measured by the electroreti- nogram and a pigmentary retinopathy are characteristic features. The condition can be inherited as an x-linked recessive, autosomal recessive, or autosomal dominant trait, and genetically retinitis pigmentosa is highly heter- ogeneous, with more than 32 loci currently mapped. 1 X-linked retinitis pigmentosa (XLRP) is the most severe type of retinitis pigmentosa, with the earliest onset and the most rapid progression, and accounts for between 10% and 20% of retinitis pigmentosa patients. 2 Although five XRRP loci have been found, RP2 on Xp11.4 accounts for 26% and RP3 on Xp21.1 for 56% to 90% of XLRP patients. 3 Until recently, only 20% of RP3-linked families were found to carry a mutation in RPGR; 4 however, a new exon, ORF 15, has been discovered that represents a mutational hotspot. 5 The RP3 gene is RPGR, the retinitis pigmentosa GT- Pase regulator, with unknown function, 6 but the gene product is associated with the centrosomes and colocalizes with microtubules of the ciliary axoneme, which are related to the connecting cilium of the outer and inner segment of photoreceptors. 7 Several XLRP families linked to RP3 have been found to have ciliary abnormalities. 8,9 In the RPGR knockout mouse, the subcellular localization of RPGR to the connecting cilium was confirmed 10 and this model shows that both retinal morphology and electroreti- nogram function are normal at the completion of retinal development. Shortly after, however, photoreceptor cell Accepted for publication March 17, 2003. From the McGill Ocular Genetics Laboratory (R.K.K., M.L., H.A.M., R.B.), Center for Research in Neuroscience (C.K.H., G.A.R.), and McGill Visual Electrophysiology Laboratory (O.D., J.R.), McGill Uni- versity Health Center Research Institute, Montreal, Quebec, Canada. Inquires to Robert K. Koenekoop MD, PhD, Montreal Children’s Hospital, Ophthalmology, 2300 Tupper, Montreal, PQ, Canada, H3H 1P3; fax (514) 412-4443; e-mail: [email protected] © 2003 BY ELSEVIER INC.ALL RIGHTS RESERVED. 678 0002-9394/03/$30.00 doi:10.1016/S0002-9394(03)00331-3

Novel RPGR mutations with distinct retinitis pigmentosa phenotypes in French-Canadian families

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Novel RPGR Mutations With Distinct RetinitisPigmentosa Phenotypes in French-Canadian

Families

ROBERT K. KOENEKOOP, MD, PHD, MAGALI LOYER, MSC, COLLETTE K. HAND, PHD,HUDA AL MAHDI, MD, OLGA DEMBINSKA, PHD, RAQUEL BENEISH, MSC,

JULIE RACINE, MSC, AND GUY A. ROULEAU, MD, PHD

● PURPOSE: To characterize the molecular defects in twox-linked retinitis pigmentosa (RP) families. We hypoth-esized that different RPGR mutations result in distinctRP phenotypes.● DESIGN: Observational case series.● METHODS: Fifteen members in family I and threemembers in family II were evaluated. Full ophthalmicevaluations were done. Linkage analyses were performedand likelihood of odds scores (LOD score) were calcu-lated. For mutation analyses, we used dHPLC and auto-mated sequencing.● RESULTS: Two novel RPGR mutations were identifiedin the two families; a Glu 414 (2-bp del) frameshiftmutation in family I and an IVS 2–1 (g to a) splice sitemutation in family II. All male family members in familyI were severely affected by RP but maintained centralvisual acuities until their 50s and did not develop a bull’seye maculopathy. The female phenotype was highlyvariable. Some of the carriers exhibited a severe pheno-type, one female displayed an asymmetric phenotype, andother carriers were asymptomatic. All members with theRPGR frameshift mutation exhibited rod-cone electro-retinograms abnormalities, whereas five members hadhearing loss. Male members of family II were severelyaffected, with early visual acuity loss, central scotomas,and bull’s eye maculopathy. The female family memberswere asymptomatic but displayed cone-rod electroretino-grams changes. There was no hearing loss.● CONCLUSIONS: Different RPGR mutations lead todistinct RP phenotypes, with a highly variable inter- and

intrafamilial phenotypic spectrum of disease that is asso-ciated with the type of mutation in RPGR and nonran-dom X chromosome inactivation, respectively. (Am JOphthalmol 2003;136:678–687. © 2003 by ElsevierInc. All rights reserved.)

R ETINITIS PIGMENTOSA (RP) IS A HIGHLY VARIABLE

group of diseases characterized by retinal degenera-tion, with progressive night blindness, loss of periph-

eral vision, and eventual loss of central vision. Progressiveloss of photoreceptor function measured by the electroreti-nogram and a pigmentary retinopathy are characteristicfeatures. The condition can be inherited as an x-linkedrecessive, autosomal recessive, or autosomal dominanttrait, and genetically retinitis pigmentosa is highly heter-ogeneous, with more than 32 loci currently mapped.1

X-linked retinitis pigmentosa (XLRP) is the most severetype of retinitis pigmentosa, with the earliest onset and themost rapid progression, and accounts for between 10% and20% of retinitis pigmentosa patients.2 Although five XRRPloci have been found, RP2 on Xp11.4 accounts for 26%and RP3 on Xp21.1 for 56% to 90% of XLRP patients.3Until recently, only 20% of RP3-linked families werefound to carry a mutation in RPGR;4 however, a new exon,ORF 15, has been discovered that represents a mutationalhotspot.5

The RP3 gene is RPGR, the retinitis pigmentosa GT-Pase regulator, with unknown function,6 but the geneproduct is associated with the centrosomes and colocalizeswith microtubules of the ciliary axoneme, which arerelated to the connecting cilium of the outer and innersegment of photoreceptors.7 Several XLRP families linkedto RP3 have been found to have ciliary abnormalities.8,9 Inthe RPGR knockout mouse, the subcellular localization ofRPGR to the connecting cilium was confirmed10 and thismodel shows that both retinal morphology and electroreti-nogram function are normal at the completion of retinaldevelopment. Shortly after, however, photoreceptor cell

Accepted for publication March 17, 2003.From the McGill Ocular Genetics Laboratory (R.K.K., M.L., H.A.M.,

R.B.), Center for Research in Neuroscience (C.K.H., G.A.R.), andMcGill Visual Electrophysiology Laboratory (O.D., J.R.), McGill Uni-versity Health Center Research Institute, Montreal, Quebec, Canada.

Inquires to Robert K. Koenekoop MD, PhD, Montreal Children’sHospital, Ophthalmology, 2300 Tupper, Montreal, PQ, Canada, H3H1P3; fax (514) 412-4443; e-mail: [email protected]

© 2003 BY ELSEVIER INC. ALL RIGHTS RESERVED.678 0002-9394/03/$30.00doi:10.1016/S0002-9394(03)00331-3

loss, outer segment disorganization, cone opsin mislocal-ization, and rhodopsin content reduction were noted,whereas the structure of the connecting cilium appearedwell maintained.

RPGR mutations have been associated with a widevariety of human clinical phenotypes, including XRRP,6XDRP,11,12 XRCRD,13,14 and, surprisingly, x-linked macu-lar degeneration with normal electroretinograms.15 In thecanine animal models, two RPGR microdeletions werereported to lead to strikingly disparate phenotypes, one anearly onset and the other a late-onset retinal degenera-tion.16 The important issue of how various mutations inRPGR can lead to significantly different clinical pheno-types remains unresolved.

We have identified two novel mutations in RPGR intwo large French-Canadian XLRP families, which allowedus to evaluate, in detail, the phenotypic spectrum of 15affected family members in family I and three members infamily II and correlate the RPGR mutations with the

resulting phenotypes. We tested the hypothesis that dif-ferent RPGR mutations lead to distinct phenotypes.

METHODS

● OPHTHALMIC EVALUATIONS: Detailed ocular and vi-sual histories were taken, pedigrees were drawn, anddetailed eye examinations were performed on all affectedand at-risk patients, including age-appropriate best-cor-rected visual acuities, cycloplegic refractions, slit-lampbiomicroscopy, and dilated indirect ophthalmoscopy.Color vision was tested by D-15 panel and by Ishiharacolor plates. Visual fields were measured by Goldmannkinetic perimetry, using the V4e and l4e test lights,moving the target from nonseeing to seeing retina. Elec-troretinograms were performed on both eyes in accordancewith the standards recommended by the InternationalSociety for Clinical Electrophysiology of Vision.17

● LINKAGE ANALYSIS: One proximal and one distal mi-crosatellite marker to four of the five XRRP loci werechosen based on linkage to the five known XLRP loci,using the genome database and OMIM (online mendelianinheritance of man database; data available on request).Microsatellite markers were typed by polymerase chainreaction, using radioactively end-labeled primers. Ampli-fication procedures are available upon request. The dis-tance traveled on the gel represents the size of thepolymerase chain reaction product, which is a directmeasure of the number of nucleotide repeats of themicrosatellite marker.

● LINKAGE DATA ANALYSIS: Pedigrees were drawn inCyrilic (2.1.3), and two-point and multipoint Likelihoodof Odds score (LOD scores) were computed using thelinkage package version 5.1 MLINK from the LINKSYSdata management and the FASTMAP software. Linkage is

FIGURE 1. Family I pedigree with four generations of XLRP. The solid figures represent the patients affected with retinitispigmentosa.

FIGURE 2. Retinal photo of patient IV-2 of family I showingthe superior retinal degeneration with bone spicule formation.

RPGR MUTATIONS IN RETINITIS PIGMENTOSAVOL. 136, NO. 4 679

accepted if LOD scores are �3.0 or greater and excluded ifscores are less than –2.0.

● MUTATION SCREENING: Genomic DNA was extractedfrom peripheral blood leukocytes after informed consentswere obtained, according to guidelines set forth by theMontreal Children’s Hospital ethical review board. Muta-tion analysis of all 19 RPGR exons, including ORF14 andORF15, was performed, using denaturing high-perfor-mance liquid chromatography. Variations detected by thismethod were further analyzed by automated sequencing.To confirm mutations and to exclude the mutation in 100ethnically matched control patients, restriction enzymedigests were performed for the IVS2–1 (g to a) mutation,and we made an artificial created restriction site for theGlu 414 (2bp del) mutation (available on request).

RESULTS

● FAMILY I GENOTYPING: Fifteen family members (9male, 6 female participants) were phenotyped (Figure 1).All affected members share a Glu414 (2bp del) (bp 1244 to1245 �GA) frameshift mutation in exon 10 of RPGR. Thismutation is predicted to result in a stop codon at position461, and likely represents a null allele.

● MALE PHENOTYPE (N � 9; SEE TABLE 1): Visual acu-ities ranged from 20/20 (age 25 years) to light perception(age 75 years) but were still 20/40 in two men in their 50s.There was no bull’s eye maculopathy. Cataracts were foundin all men older than 40 years. Goldmann visual fields(V4e) were reduced to 10 degrees or less in six of the menwho were in their late 40s or older. The electroretinogramswere nondetectable in these six men, whereas the rod andcone electroretinograms were reduced to 10% of normal inthe 8-year-olds and 18-year-olds. All male participants hadsevere, diffuse retinal degeneration with choroidal sclerosisand bone spicule formation. Exceptions were the regionalretinal pigmentation (superiorly) in IV-1 (Figure 2) anddiffuse white retinal dots in IV-6.

● FEMALE PHENOTYPE (SEE TABLE 1): The two severelyaffected female participants reported onset at ages 15 and27 (Figures 3 and 4). Both reported hearing defects, andone was found to have a speech impediment. One femaleparticipant (III-9) had severe symptomatic disease in theleft eye and mild, asymptomatic disease in the right eye.Symptoms commenced at age 17 (Figure 5). Three asymp-tomatic female participants were tested, and their electro-retinograms ranged from within normal limits, to mildrod-cone abnormalities (Figure 6). The fundus showedmild hypopigmented areas (Figure 7).

TABLE 1. Phenotypic Measures of Members of Family I and Family II

Pt. No. Age Onset Optics Acuity VF

Rod

ERG �V

Cone

ERG �V

Hearing

Loss

I

1 III-15 M 51 19 20/40 10 ND ND

2 III-16 M 49 13 20/150 5 ND ND

3 III-17 M 57 14 20/50 5 ND 6

4 III-18 M 55 15 20/80 10 ND 15

5 IV-6 M 8 8 20/20 80 15 22

6 IV-1 M 18 12 20/30 60 12 12

7 II-11 M 76 5 LP 0 ND ND Yes

8 IV-2 M 25 15 20/20 15 – – Yes

9 III-11 M 52 6 20/40 10 ND ND

10 II-5 F 74 Asx �2.00 20/30 80 85 59 Yes

11 III-8 F 45 Asx Plano 20/20 80 110 90

12 III-28 F 46 Asx �3/�7 20/30 80 229 114

13 III-9 F 42 17 �9/�8 20/60 SL ND/ ND/

20/20 80 28 28

14 III-13 F 48 27 �7.00 20/70 5 ND ND Yes

15 III-23 F 52 15 �5.00 HM

20/30

10 ND ND Yes

II

1 IV-3 M 9 7 �7.25 20/40 55 ND 22

2 IV-4 M 13 6 �7.00 20/50 45 ND 10

3 III-5 F 41 Asx �10.00 20/20 70 145 55

ERG � electroretinogram; ND � nondetectable; Pt � patient; VF � visual field.

AMERICAN JOURNAL OF OPHTHALMOLOGY680 OCTOBER 2003

● FAMILY II GENOTYPING (SEE FIGURE 8): All affectedmembers share the splice site mutation IVS2 to 1 (g to a).This mutation likely represents a null allele, because thesplice donor site is altered and is predicted to lead to atruncated protein.

● MALE PHENOTYPE (N � 2; SEE TABLE 1): Two youngmale participants reported disease onset (night blindness)at ages 7 and 6. They also reported early visual acuity loss.Best-corrected visual acuities were 20/40 and 20/50 in botheyes with high myopic astigmatic corrections (�7.50 �2.00 � 180 degrees in the right eye, �7.00 � 1.50 � 20degrees in the left eye for the 9-year-old, and –7.00 � 2.00� 160 degrees in the right eye, �7.00 � 2.00 � 175degrees in the left eye for the 13-year-old). Both D-15 andIshihara tests were normal for both these participants.Their visual fields were markedly constricted, especially

FIGURE 3. Phenotype of a severely affected woman from family l at age 52 years (Patient 15, III-23). (A) Goldmann visual fields(V4e and l4e targets) of the left and right eye. (B) Photopic and scotopic electroretinograms showing the retinal responses of theright and left eyes. (C) Photopic electroretinogram (ERG) of both eyes. (D) Scotopic electroretinogram of both eyes.

FIGURE 4. Retinal photo of Patient III-23 showing severe,diffuse retinal degeneration.

RPGR MUTATIONS IN RETINITIS PIGMENTOSAVOL. 136, NO. 4 681

nasally, and we documented a relative central scotoma(O3e; Figure 9). Electroretinograms were nondetectable ormarkedly reduced. Both exhibited bull’s eye maculopathy.

● FEMALE PHENOTYPE: The mother of these two boyswas asymptomatic at age 41 with visual acuities of 20/20 inboth eyes (with �10.00 � 1.00 � 95 degrees in the righteye, �10.00 � 1.00 � 80 degrees in the left eye). Bothcolor vision tests and visual fields (Figure 10) were normal.The electroretinogram was abnormal, unlike the electro-retinogram of the asymptomatic carriers of Family l. Therod mediated b-wave amplitudes were reduced to 73% ofnormal, and the cone mediated b-wave amplitudes werereduced to 46%. On retinal examination, we found mild,pigmentary changes but no bull’s eye maculopathy, nor did

we find a tapetal sheen. No members of this familyreported hearing loss.

DISCUSSION

AS IN PREVIOUS STUDIES,19,22–24 WE SHOW IN OUR FAMILIES

that RPGR mutations cause a severe XRRP phenotype inthe boys and men with an average onset at age 12 in familyI and age 6 in family II. Visual acuities ranged from 20/20to light perception in family I (with the frameshift muta-tion), but several male participants maintained 20/40acuities in their 50s; we did not find a bull’s eye maculopa-thy. In family II (with the splice site mutation), however,the male phenotype was distinctly different, because visual

FIGURE 5. Phenotype of a severely affected asymmetric woman from family I at age 42 years (Patient 13, III-9). (A) Goldmannvisual fields (V4e and 14e targets) of the left and right eye. (B) Photopic and scotopic electroretinograms showing the retinalresponses of the right and left eyes. (C) Photopic electroretinograms (ERG) of both eyes. (D) Scotopic electroretinograms of botheyes.

AMERICAN JOURNAL OF OPHTHALMOLOGY682 OCTOBER 2003

acuities were already decreased to 20/50 in the 13-year-oldboy and to 20/40 in the 9-year-old boy; relative centralscotomas (O3e) were found on visual field with a bull’s eyemaculopathy. In both families, retinitis pigmentosa pro-gressed rapidly, and a male from family I was found to belegally blind, with 15 degrees visual fields at age 25. Alsoin the male participants, the electroretinograms werenondetectable after age 40, whereas the rod electroretino-gram amplitudes were below 10% of normal by the earlyteenage years in both families. Cone electroretinogramamplitudes were found to be approximately 25% of normalin the teenagers from both families.

RPGR mutations can also cause a severe retinitis pig-mentosa phenotype in girls and women. In family I, thefemale disease onset averaged age 20, and legal blindnesswas noted in the early 40s, which is 10 years later for onsetand 15 years later for legal blindness than among the male

participants. Of interest is the fact that RPGR mutationscan cause asymmetric, asymptomatic, and severe retinitispigmentosa in girls and women, all in the same family,with the same mutation. This diversity of female retinitispigmentosa phenotypes is likely the result of nonrandom orunfavorable X chromosome inactivation. Random inacti-vation of one of the X chromosomes usually results inpatchy mild retinitis pigmentosa in female XLRP carriersaccording to the Lyon hypothesis. Severe, diffuse panreti-nal disease in our female participants with RPGR muta-tions may be the result of nonrandom inactivation of theX chromosome in both retinas, or perhaps of retinal celldeath in cells neighboring those that express the RPGRmutation, by direct toxic effects or loss of trophic support.It is conceivable that the variability of the female pheno-type is also RPGR-mutation specific. We were surprised tofind three female participants, one of them 75 years old,

FIGURE 6. Phenotype of an asymptomatic, mildly affected woman from family I at age 74 years (Patient 10, II-5). (A,B)Goldmann visual fields (V4e and 14e targets) of the left and right eye. (C,D) Photopic and scotopic electroretinograms (ERG)showing the retinal responses of the right and left eyes.

RPGR MUTATIONS IN RETINITIS PIGMENTOSAVOL. 136, NO. 4 683

who were asymptomatic and on careful phenotyping ex-hibited only mild retinal disease. We were also surprised tofind a female participant with marked asymmetry of dis-ease; one eye exhibited random inactivation of the Xchromosomes resulting in mild, patchy asymptomatic dis-ease, and nonrandom X chromosome inactivation in thefellow eye resulted in severe, diffuse panretinal disease.

Most female carriers of XLRP have mild pheno-types,20–24 but severely affected carriers have been report-ed.11 Fishman and associates20 found that 39 of 46 (85%)of XRRP carriers have subtle retinal changes or function(or both) including myopia, tapetal reflex, peripheralpigment changes, small changes in visual acuity, or subtlechanges in electroretinogram measurements. In 5 of 46XRRP carriers (10%) visual acuity and in 7 of 46 carriers(15%) electroretinogram measures were severely affected,but genotyping was not yet available. A longitudinal studyof visual function of 27 XLRP carriers by Grover andassociates21 found that most carriers (20 of 27; 75%) wereclassified as grade 0, which represents patients with anormal retinal appearance; grade 1, which represents a

FIGURE 7. Retinal photo of Patient II-5 showing a mildinferior retinal patch of hypopigmentation.

FIGURE 8. Family II pedigree with X-linked retinitis pigmentosa. The solid figures represent the patients affected with retinitispigmentosa.

AMERICAN JOURNAL OF OPHTHALMOLOGY684 OCTOBER 2003

tapeto-retinal reflex; or grade 2, which represents patchyretinal disease. In contrast, 7 of 27 (25%) carriers exhib-ited diffuse retinal disease, which was designated grade 3.After an average of 14 years of follow-up, none of the grade0 or grade 1 patients, but a significant percentage of grade2 and 3 carriers had deterioration of acuity, visual field size,or electroretinogram amplitudes (or a combination of thesesigns). This classification is likely valid because none of thecarriers changed grade over the average follow-up period of14 years (range, 4–26 years). Rozet and associates12 iden-tified nine null RPGR alleles (in ORF15) in XLRP patientsand reported severely affected female carriers, but a de-tailed phenotype analysis was not reported. They suggestedthat RP3 is an incomplete dominant X-linked type ofretinitis pigmentosa and that in some girls and women, nopreferential X chromosome inactivation occurs.

Not all RPGR mutations are associated with a severefemale phenotype. In studies that relate the phenotype tothe genotype, Fishman and associates22 found a 2 bpdeletion in exon 13 of RPGR and a severe, early-onset

male phenotype, but all three female obligate carriers wereasymptomatic with mild myopia (�2.50), mild visualacuity changes (20/25), patchy pigmentary retinopathy,normal visual fields, and normal electroretinogram mea-surements. Fishman and associates23 found two familieswith a missense mutation in exon 3 of RPGR, reporting asevere phenotype in the male family members and a mildpatchy retinopathy in the carriers, with involvement of thesuperotemporal quadrant of the visual field. Jacobson andassociates24 found a Gly52stop RPGR mutation with a mildto severe disease expression in the carriers and severephenotype in the male participants.

Different RPGR mutations can cause divergent retinitispigmentosa phenotypes, also in boys and men. Our splicesite mutation was associated with two boys who experi-enced early loss of visual acuity at age 7 (20/40) and age 13(20/50), relative central scotomas (O3e), and a bull’s eyemaculopathy, whereas the frameshift mutation was associ-ated with male participants who maintained 20/20 visualacuity at age 25 and 20/40 acuities at age 52. We did not

FIGURE 9. Phenotype of a severely affected boy from family II at age 13 years (Patient 2, IV-3). (A,B) Goldmann visual fields(V4e and 14e targets) of the left and right eye. (C,D) Photopic and scotopic electroretinograms (ERG) showing the retinal responsesof the right and left eyes.

RPGR MUTATIONS IN RETINITIS PIGMENTOSAVOL. 136, NO. 4 685

detect any color vision defects in the male participantswith the visual acuity loss; however, it appears that someRPGR mutations (splice site mutation in family II) cancause early central cone photoreceptor abnormalities,whereas other mutations in RPGR (frameshift mutation infamily I) cause visual acuity loss later in the diseaseprocess. This observation is strengthened by the electro-retinogram findings in the carrier mother of the two boyswith the early visual acuity loss. The female carrier withthe splice site RPGR mutation was found to have anabnormal electroretinogram with more cone than rodmediated amplitude losses, whereas the female carrierswith the frameshift mutation exhibited normal, equallyaffected cone and rod or rod more affected than coneelectroretinograms, but not cone more affected than rod, asin the carrier of Family II. This suggests that the electro-retinogram of the carriers may be predictive of the visualacuities of the male offspring. Whether these findings havegeneral applicability must await further genotype-pheno-type studies with RPGR and XRRP.

Five participants in family I were found to have hearingdefects, whereas one female participant was also found to

have a speech deficit, probably the result of a mild hearingdefect from early childhood. All patients with hearing losscarried the RPGR frameshift mutation, whereas none ofthe nonaffected patients (without the RPGR mutation)had hearing loss. Although not all patients were tested, itis conceivable that hearing loss is also a variable expressionof this RPGR mutation. No patients reported sinus disease,respiratory problems, or infertility. Zito and associates9

reported sinusitis, recurrent lung infections, and conduc-tive hearing defects in some of the retinitis pigmentosapatients with RPGR mutations in ORF15. Because RPGRis widely expressed in the human body and RPGR isassociated with the microtubules of the ciliary axoneme,which are also found in the hair cells of the inner ear, it ispossible that the hearing defects are caused by variableexpression of the mutant RPGR.

In summary, we report two novel RPGR mutations, aframeshift (Gly 414 2 bp del) and a splice site mutation(IVS 2–1 g to a) in two French-Canadian families, anddescribe the resulting phenotypes in 15 and 3 familymembers, respectively. We found striking differences be-tween the two families. In the family with the frameshift

FIGURE 10. Phenotype of an asymptomatic, mildly affected woman from family II at age 41 years (Patient 3, III-5). (A,B)Goldmann visual fields (V4e and 14e targets) of the left and right eye. (C,D) Photopic and scotopic electroretinograms (ERG)showing the retinal responses of the right and left eyes.

AMERICAN JOURNAL OF OPHTHALMOLOGY686 OCTOBER 2003

mutation, we found a severe, peripheral retinal degenera-tion in the male and some of the female participants,whereas the rod-mediated and cone-mediated electroreti-nograms were equally affected and visual acuity was af-fected relatively late (around age 50) in the diseaseprocess. Five members were found to have hearing loss. Inthe family with the splice site mutation, we found early-onset loss of visual acuity, relative central scotomas, and abull’s eye maculopathy in the male family members inaddition to a severe rod-cone degeneration. An early coneinvolvement in the female carrier was evident on thecone-mediated electroretinogram; there was no reportedhearing loss.

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