Clinical and Functional Findings in Choroideremia Due to Complete Deletion of the CHM Gene

OPHTHALMIC MOLECULAR GENETICS Clinical and Functional Findings in Choroideremia Due to Complete Deletion of the CHM Gene

Marco Mura, MD; Christina Sereda, BS; Monica M. Jablonski, PhD; Ian M. MacDonald, MD; Alessandro Iannaccone, MD, MS

Objective: To report the clinical, functional, and in vivo illaris atrophy. The carrier mother had diffuse elevation microanatomic characteristics of a family with choroi- of 650-nm dark-adapted thresholds. deremia with a deletion of the entire gene that encodes for the Rab escort protein 1 (CHM). Conclusions: Deletion of the CHM gene causes severe choroideremia. Results of serial ERGs and fundus ex- Methods: We performed clinical examination, flash elec- aminations documented progression first of rod and then troretinography (ERG), light- and dark-adapted perim- of cone disease. Fundus appearance deteriorated rap- etry, and optical coherence tomography; reviewed medi- idly, in excess of the severity of the ERG decline. Opti- cal records; and obtained the medical history of the cal coherence tomography findings explained this ob- proband and 3 other family members. servation, at least in part.

Results: At 4 years of age, the proband had a hypopig- Clinical Relevance: To our knowledge, this is the ear- mented fundus and retinal pigment epithelium mot- liest clinical, microanatomic, and ERG longitudinal tling, and dark-adapted ERGs were reduced. Severe reti- phenotypic documentation in molecularly character- nal pigment epithelium and choriocapillaris atrophy ized choroideremia and the first documentation of im- developed by 6 years of age, paralleled by a lesser ERG decline. Optical coherence tomography findings showed paired dark-adapted cone function in carriers. The pres- normal neural retinas overlying mild changes in the reti- ervation of the neural retina has mechanistic, prognostic, nal pigment epithelium and thinned neural retina with and therapeutic implications. impaired lamination, yet the neural retina was fairly preserved over retinal pigment epithelium and choriocap- Arch Ophthalmol. 2007;125(8):1107-1113

HOROIDEREMIA IS A PRO- tions in molecularly characterized pa- gressive X-linked reces- tients; and the disease mechanisms remain sive retinal disease caused incompletely understood. by mutations in the CHM Herein we report the phenotype of gene, which encodes for members of a family resulting from the un- theC Rab escort protein 1 (REP-1).1 In af- common lack of the entire CHM gene. Spe- fected males, choroideremia is character- cifically, we had the opportunity to char- acterize disease expression and progression Author Affiliations: Retinal ized clinically by areas of scalloped atro- Degeneration and Ophthalmic phy of the retinal pigment epithelium in the proband in his early childhood years Genetics Service, Hamilton Eye (RPE), choriocapillaris (CC), and retina.2,3 by clinical criteria, functional testing, and in vivo imaging methods. We also con- Institute, University of Although the exact function and cellular ducted in-depth functional studies on an Tennessee Health Science localization of REP-1 in the eye remain in- Center, Memphis (Drs Mura, obligate carrier, documenting abnormali- Jablonski, and Iannaccone); and completely understood, REP-1 appears to ties of visual function in the dark- Department of Ophthalmology, be necessary in cellular processes as a regu- adapted state that, to our knowledge, had Ophthalmic Genetics lator of signal transduction, protein traf- not been previously reported in carriers. Laboratory, University of ficking, and endocytosis.4 Most CHM mu- Alberta, Edmonton (Ms Sereda tations result in a truncated REP-1 product and Dr MacDonald). Dr Mura is and include complete gene deletions.5,6 METHODS now with the Department of Ophthalmology, Academic Genotype-phenotype correlations re- Medical Center, University of main unclear, with instances of clinical The pedigree is illustrated in Figure 1. On re- 6 Amsterdam, Amsterdam, heterogeneity ; limited information is avail- ferral, the proband (individual V:1) did not have the Netherlands. able on the early phenotypic manifesta- visual symptoms. The family history was posi-

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©2007 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/29/2021 images from comparable retinal locations were obtained and analyzed from an age-matched control subject. I:1 I:2 The resulting images were analyzed manually with Na- tional Institutes of Health Image J software (version 1.36; http: //rsb.info.nih.gov/ij/). The correct scale was set by calibrating the software to the retinal thickness measured at the fovea by II:1 II:2 II:3 the OCT automated retinal thickness software (version 4.0.1; StratusOCT), which does not include the first hyperreflective band (shown in red in the false-color OCT maps) of approxi- III:1 III:2 III:3 III:4 III:5 III:6 III:7 III:8 mately 20 to 25 µm attributable to photoreceptor inner and outer segments. For the purpose of comparing our findings more di- rectly with those of Jacobson et al,11 measurements of total neural retinal thickness were conducted at the fovea and at 1.3 mm IV:1 IV:2 IV:3 IV:4 IV:5 IV:6 of eccentricity from the fovea on magnified views of the images over adjacent pixel columns at these locations. However, ? ? ? our total neural retinal thickness measurements included the V:1 V:2 V:3 V:4 V:5 V:6 first hyperreflective photoreceptor inner and outer segment band P but not the second one, which is instead attributable to the RPE. The thickness of the outermost hyporeflective band in the OCT

Male Affected P Proband Monozygotic profile attributable to the outer nuclear layer (ONL) was also twins estimated. We performed identical measurements at 3.0 mm Female Unaffected Obligate Dizygotic temporal to the fovea, in an area of neural retina overlying a carrier twins large nummular area of RPE/CC atrophy. All measurements were Unknown Deceased Unknown Divorced sex status averaged and are expressed as mean±SD. Comparisons are given with our normal control image and the reference ranges that could be derived from Jacobson et al.11 Also, because in the lat- Figure 1. Pedigree of the family with choroideremia. ter study total retinal thickness measurements included the RPE peak,11 we enhanced comparability between their study and ours by reducing the published reference ranges by 30 µm, which tive for night blindness and a progressive X-linked recessive is our estimated average thickness of the RPE hyperreflective retinal dystrophy. In addition to the proband, 3 other subjects band and the intervening thin yellow-white band above it. (his mother [IV:2] and his 2 male siblings [V:2 and V:3]) were examined. The gathering of a medical history and a review of medical records were used to obtain information about the 5 MOLECULAR GENETICS males in generation III with advanced disease. After obtaining informed consent, a whole-blood sample was FUNCTIONAL TESTING collected by venipuncture from the proband, his 2 male siblings, and their mother. Genomic DNA was extracted with a Full-field flash electroretinograms (ERGs) were recorded with a commercially available kit (QIAamp 50 Maxi Kit; Qiagen Inc, digital system (Nicolet Spirit; Viasys Nicolet Biomedical, Madi- Valencia, California) according to the manufacturer’s specifi- son, Wisconsin), in response to flashes ranging from −2.1 to 1.0 cations. Molecular genetic analyses of the CHM gene were con- log candela (cd)·s/m2 in intensity, with monopolar contact lens ducted at the University of Alberta. The CHM primers were modi- electrodes (ERG Jet; Universo Plastique AS, Grenchen, Switzer- fied from van Bokhoven et al.5 Reactions were performed in total land) as reported previously.7 The International Society for Clini- volumes of 25 µL (2.5 µL 10ϫNEB buffer [New England Bio- cal Electrophysiology of Vision “standard flash”8 was 0.32 log cd·s/ labs, Ipswich, Massachusetts], 2.5 µL of 2mM deoxyribonucleo- m2. In individual V:1, responses were obtained with the person tide triphosphates, 0.125 µL bovine serum albumin, 60-ng for- under full anesthesia (intravenous propofol infusion). ward primer, 60-ng reverse primer, double-distilled water to Monochromatic automated perimetry was performed as pre- volume, 50-ng genomic DNA, and 1 U Taq [New England Bio- viously reported,7 based on the methods developed by Jacobson labs]). The cycling settings were as follows: 95°C for 5 min- et al9 and Apa´thy et al.10 In brief, red/green cone-mediated thresh- utes (95°C for 1 minute, ␹°C for 1 minute, and 72°C for 1 olds were determined in the light-adapted state (white standard minute)ϫ40 cycles, and 72°C for 7 minutes where the anneal- background) with a 600-nm (orange) stimulus. Dark-adapted ing temperature ␹ was 50°C (exons 2, 5B, 6, 7, 8, 9, 14, and thresholds were measured after 40 minutes of dark adaptation 15), 52°C (exons 3, 5A, 11, 12, and 13), and 58°C (exons 1, 4, in response to 650-nm (red) and 500-nm (blue-green) stimuli. and 10). Polymerase chain reactions (PCRs) were run on 1% agarose gels with a 1-kilobase (kb) pair DNA ladder. OPTICAL COHERENCE TOMOGRAPHY All research studies conducted in this investigation were approved by the institutional review boards of the participat- Retinal microanatomy was investigated in individual V:1 with ing institutions and were in compliance with the Declaration an optical coherence tomography (OCT) device (StratusOCT; of Helsinki. Carl Zeiss Meditec, Dublin, California). To retain maximal spa- tial resolution with each scan, 3 or four 6-mm images were ob- RESULTS tained along the horizontal meridian (each with a density of 512 A-scans), to include areas of clinically intact macular retinal RPE and CC and areas of ophthalmoscopically visible at- PROBAND (V:1) rophy. The collected images were exported and manually merged using image-editing software (Photoshop, version 7.0.1; Adobe At baseline, visual acuity was 20/50 OD and 20/30 OS. Systems Inc, San Jose, California), yielding a single horizontal Results of the posterior segment examination showed a composite image spanning most of the posterior pole. Custom hypopigmented fundus with normal optic discs, border-

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©2007 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/29/2021 line retinal vessels, coarse macular mottling, and A punctate midperipheral RPE clumping (Figure 2A). Dis- crete RPE/CC atrophy was noticeable only in the peripapillary region and in small nummular lesions above and below the disc. Full-field flash ERGs (Figure 3) showed subnormal rod-driven responses (10% of our lowest reference limit7) and attenuated mixed dark-adapted rod- cone a and b waves (about 45% and 60% of our lowest reference limits,7 to 0.32 log cd·s/m2 and to 50% and 80% to 1.0 log cd·s/m2 stimuli), with a relatively better preservation of the b waves. Light-adapted cone-driven ERGs were delayed in timing. Findings were highly suggestive of early-stage choroideremia. To verify this impression, the CHM exons were amplified from genomic DNA by means of PCR. No product could be obtained for any of the CHM exons amplified from the proband, whereas a control autosomic gene B (VMD2) amplified normally (not shown). Although additional fluorescent in situ hybridization and protein expression studies could not be performed, these findings were consistent with a deletion of the whole CHM gene. This presumed deletion was further characterized, dem- onstrating that it incorporated a 57-kb region upstream of exon 1, excluding marker pJ7.6B, and a downstream region of at least 2.9 kb, including marker WI-11849 (not shown). Consistent with her carrier status, a product could instead be obtained from the wild-type allele for every maternal exon. This finding confirmed the clinical diagnosis of choroideremia in the proband and predicted no REP-1 transcript for affected males and in all clones har- C boring the mutated allele in female carriers. At 5 years of age, symptoms of night blindness had developed in the proband, accompanied by a remarkable increase in the extension of the lesions with large irregular and confluent patches of RPE/CC atrophy in the midperiphery and in the peripapillary and parapapillary areas (Figure 2B). The RPE mottling and clumping had increased in coarseness in most retinal quadrants. Re- peated ERG testing (Figure 3) showed a decline in both the size and quality of the dark-adapted responses. Mixed ERG responses were significantly reduced in amplitude compared with baseline, with an approximately equal re- duction in a and b waves (about 30% of the lowest limit of normal). There was no change in photopic ERGs. By 6 years of age, visual acuity was unchanged, but wide- spread coalescent areas of severe nummular RPE/CC atrophy had developed, sparing only the centermost macular region (Figure 2C). Results of further serial testing Figure 2. Composites of the fundus in the proband (individual V:1) at ages 4 years (A), 5 years (B), and 6 years (C). Progressive development of confluent (Figure 3) demonstrated an additional decline in dark- areas of nummular atrophy of the retinal pigment epithelium and adapted ERG amplitudes and sensitivity. At this stage, cone choriocapillaris can be appreciated. ERG amplitude loss was also apparent, especially to transient stimuli. Despite functional evidence of disease progression, ERG responses remained remarkably well pre- compensatory increase in the gain of postreceptoral reti- served compared with the deterioration in fundus nal neurons, a phenomenon that is often observed clini- appearance. This finding suggested 2 possible and not mu- cally in retinal dystrophies and that has been shown to oc- tually alternative explanations. First, the neural retina may cur at the animal level in rats harboring the P23H mutation be better preserved than what was suggested by the oph- of the rhodopsin gene (RHO).13 To test the former hypoth- thalmoscopic appearance and, specifically, the neural retina esis, the in vivo microanatomy of the posterior pole of the overlying areas of clinically overt RPE/CC atrophy may be proband was studied. largely intact, a possibility that has already been sug- Figure 4 illustrates a red-free view of the posterior gested by previous clinical observations.12 Second, the bet- pole of individual V:1. The results of these measure- ter-than-expected b wave preservation may result from a ments are summarized in the Table. Despite the coarse

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©2007 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/29/2021 Healthy subject CHM patient CHM patient CHM patient CHM carrier (age 4 y) (age 5 y) (age 6 y) 150 µV 150 µV 75 µV 75 µV 25 µV 20 ms – 2.10 20 ms 20 ms 20 ms 20 ms – 1.26 100 µV – 0.31 100 µV 20 ms 20 ms 0.32 100 µV Dark-Adapted

2 20 ms 1.00 s/m

⋅

50 µV 0.32 100 µV 50 µV 50 µV

Flash, log cd 12.5 ms 12.5 ms 12.5 ms 12.5 ms 100 µV 1.00 12.5 ms

100 µV 50 µV 50 µV 0.32 50 µV Light-Adapted 15 ms 15 ms 15 ms 15 ms 1.00 100 µV 15 ms

Figure 3. Flash electroretinogram responses. The responses recorded from the proband (individual V:1) during follow-up and from the obligate carrier mother (individual IV:2) are shown compared with a set of responses from a healthy subject. The arrows identify flash onset for transient responses. CHM indicates choroideremia.

tense back-scattering in the OCT image (Figure 4). At this location, total retinal thickness was reduced only to 90% of the lowest reference limit. However, consistent with what has recently been reported by Jacobson et al,11 retinal lamination was irregular and the limits of the ONL were not clearly distinguishable, precluding the mea- surement of its thickness at this location.

FEMALE CARRIER (IV:2)

The 39-year-old obligate carrier showed a classic fundus appearance with streaky patches of coarse RPE mottling, deep retinal pigmentary deposits, and peripapillary RPE/CC atrophy (Figure 5A). Her only symptom was difficulty seeing at night. The ERG testing, however, showed responses (Figure 3) that were at or above the 97th percentile in amplitude and normal timing (not CHM shown) at all flash intensities. To determine whether the night vision problem was Normal accounted for by patches of retinal dysfunction in the dark- adapted state that were too small to affect the mass Figure 4. Red-free view of the posterior pole of the proband (individual V:1) retinal response of the ERG, light- and dark-adapted (right eye) (top). The horizontal white line across the red-free image thresholds were measured. Light-adapted red/green cone- identifies the location of the optical coherence tomographic (OCT) custom mediated thresholds were essentially within reference lim- image (middle). A normal OCT image aligned to corresponding anatomic locations is shown for comparison (bottom). The ruler measures 3 mm from its throughout the entire visual field (Figure 5B). Un- the fovea toward the temporal retina. The asterisks identify location of whole expectedly, 500-nm dark-adapted thresholds were within neural retina and outer nuclear layer thickness measurements. CHM reference limits except for elevations at a few peripheral indicates choroideremia. loci in the left eye, whereas 650-nm fully dark-adapted thresholds were markedly elevated at all tested loci in both RPE mottling that is evident in the red-free image, mea- eyes, in the left more so than in the right eye, and espe- surements at the fovea showed normal thickness of the cially at extramacular loci (by about 1.0 and 1.5-2.0 log retina and a minimally thinned ONL. At 1.3 mm of ec- U at macular and extramacular loci, respectively). centricity, further RPE dropout and thinning can be seen in the red-free image. At this location, retinal thickness OTHER MALE SUBJECTS IN THE FAMILY was again within the reported reference range. The ONL was clearly discernible, as in the normal example, and The affected males in generation III (individuals III:2, III:4, at the lowest reference limit in thickness. At 3.0 mm of III:6, and III:7), who were in the seventh and eighth de- eccentricity, a large area of nummular RPE/CC atrophy cades of life when examined, experienced night blind- can be seen ophthalmoscopically and is identified by in- ness and peripheral visual field loss by the middle to late

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OCT Thickness, µm

No. of Individual V:1, Control Subject, Normal Location, Layer A-Scans Mean ± SD Mean ± SD Rangea Fovea Neural retina 5 173.3 ± 4.5 173.9 ± 3.1 140-210 ONL 9 97.7 ± 2.9 108.4 ± 3.3 NA 1.3-mm eccentricity Neural retina 5 269.5 ± 0.8 282.6 ± 5.1 250-310 ONL 5 50.7 ± 3.6 81.0 ± 5.6 52-85 3.0-mm eccentricity Neural retina 12 154.3 ± 4.8 226.0 ± 5.3 170-240 ONL ... NM ......

Abbreviations: NA, not available; NM, not measurable; OCT, optical coherence tomography; ONL, outer nuclear layer; ellipses, not applicable. a Values are based on the published ranges of Jacobson et al.11

A B OS S 600-nm LAS OD dB loss 36 24 0 12 1-5 T N N 6-10 T 0 11-15 12 16-20 24 ≥21 36 48 I I

S 650-nm DA S dB loss 36 24 0 1-5 12 6-10 T N N T 0 11-15 12 16-20 24 21-25 36 26-30 48 ≥31 I I

S S Degrees of Eccentricity From Fovea 500-nm DA dB loss 36 24 0 12 1-5 TNN T 0 6-10 11-15 12 16-20 24 21-25 36 26-30 48 31-35 I I 36-40 ≥41 72 60 48 36 24 12 0 12 24 36 4848 36 24 12 0 12 24 36 48 60 72 Degrees of Eccentricity From Fovea

Figure 5. Composite of the fundus (A) and monochromatic automated perimetry (B) for the obligate carrier mother (individual IV:2). Classic signs of choroideremia carrier status are ophthalmoscopically evident. Prominent sensitivity loss to 650-nm but not to 500-nm dark-adapted (DA) stimuli is bilaterally evident across the visual field. dB indicates decibel; I, inferior; LA, light adapted; N, nasal; S, superior; and T, temporal.

third decade and were severely affected, with light per- there were no symptoms or fundus changes suggestive ception vision only or otherwise legal blindness. Indi- of choroideremia. The provisional clinical diagnosis of viduals III:2 and III:6 retained sufficient vision to be able unaffected status for these brothers was confirmed at the to drive a car until aged 40 to 45 years, whereas indi- molecular level by normal PCR amplification of all CHM viduals III:4 and III:6 were reportedly never able to drive. exons (not shown). Individual III:1 died young but was reportedly already legally blind by the middle of the third decade of his life. REVIEW OF SYSTEMS Individuals V:2 and V:3, the proband’s brothers, were first examined at 4 and 3 years of age, respectively, at Because the deletion encompassed regions upstream and which time they had normal visual acuity, a hypopig- downstream from CHM, and because complex syn- mented fundus with nonspecific RPE mottling, and no dromic choroideremia phenotypes in association with de- overt sign of choroideremia (not shown). At subse- letions of the X chromosome have been previously re- quent yearly examinations, the mottled appearance of the ported,14-19 a detailed review of systems was performed RPE was unchanged, there was an increase in the my- in the affected male members and the female carrier par- opic refraction but no deterioration in visual acuity, and ticipating in this study. With the exception of an unusu-

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©2007 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/29/2021 ally high rate of twin pregnancies in obligate carriers mechanism of retinal disease in choroideremia carriers (Figure 1), none of the aforementioned subjects in this may not necessarily be the same as in affected males. In family showed any contributory systemic finding, thereby addition, it must be remembered that the RPE and the indicating that the deletion affecting the CHM gene in neural retina are embryologically distinct tissues. In fe- this family was not associated with any clinically overt males, who are mosaics for the disease allele, the clones systemic manifestation. of RPE and photoreceptor cells expressing the mutant allele will not always correspond to one another. There- fore, the fundus of females can show either one of the COMMENT following: (1) wild-type RPE clones juxtaposed to wild- type photoreceptor clones; (2) wild-type RPE juxta- To our knowledge, this is the earliest clinical, microana- posed to mutant photoreceptors; (3) mutant RPE juxta- tomic, and ERG longitudinal phenotypic documentation posed to wild-type photoreceptors; or (4) RPE and in molecularly characterized choroideremia and the first photoreceptor mutant clones. These observations may study of impaired dark-adapted cone function in carriers. help explain why, in human female carriers23 or in mouse Consistent with the predicted complete absence of REP-1 heterozygote null CHM females,24 photoreceptor and RPE associated with a deletion of the entire CHM gene and the disease appear to occur independent of one another. findings of Ponjavic et al6 in another such family, despite Hence, extrapolation of female data to male disease must the initial preservation of rod and cone function that both be approached with caution. In very young boys, based studies documented, the entire absence of the CHM gene on our serial clinical and functional findings and the OCT is associated with severe choroideremia. Serial ERGs in our data, changes in the RPE appear to precede degenera- proband also demonstrated progression of rod disease early tion of the overlying neural retina. This is consistent with on, followed by cone disease, consistent with the hypoth- findings from a zebra fish choroideremia model25-27 and esis of greater rod than cone vulnerability to compro- largely also with the findings of Jacobson et al.11 mised REP-1 function in affected males.6,20 Despite the thinning and impaired retinal lamination The deterioration in fundus appearance was strikingly seen in our proband and by Jacobson et al at sites of com- rapid and exceeded the severity of the ERG losses. The clini- plete RPE/CC atrophy, ERG responses suggest that these cal impression that the retina overlying areas of RPE/CC portions of the neural retina are still contributing to the atrophy may be well preserved in choroideremia, already signals and are therefore still viable. We find this appar- suggested by Sieving12 and supported by our ERG find- ent ability of the neural retina to survive in these areas of ings, was corroborated by the OCT studies. The OCT find- clearly compromised RPE/CC integrity remarkable and of ings showed progressive retinal thinning and abnormal lami- therapeutic and prognostic relevance. Notwithstanding the nation proportional to the severity of RPE damage, the latter foreseeable future role of gene therapy,28 we suggest (1) always being ophthalmoscopically visible in areas with nor- that treatments that could restore the integrity of the RPE mal retinal thickness and microanatomic structure, and re- or compensate for its compromise may also represent an markable preservation of neural retinal tissue in areas of effective treatment strategy for choroideremia and (2) that complete RPE/CC atrophy. In these latter areas, however, retinal areas overlying complete RPE/CC atrophy may still retinal lamination was already compromised, the limits of be salvaged, at least at disease stages as early as that of our the ONL were uncertain, and some degree of thinning could proband. Examples of such treatments may be RPE trans- be documented, which is consistent with the findings of plants29 and/or sustained intraocular delivery of pigment Jacobson et al11 in children older than our proband. Short- epithelium–derived factor,30-32 a molecule that has been ening of the photoreceptor inner and outer segments in areas shown to have potent neuroprotective effects on photo- corresponding to RPE/CC atrophy is also likely, whereas receptors deprived of the support of RPE33-37 and to pre- no significant changes in the OCT variables were seen at vent the Mu¨ ller cell changes resulting from this depriva- locations of ophthalmoscopically apparent RPE distur- tion.34,35,37 Mu¨ ller cell changes are now postulated to play bance. a role in neural retinal remodeling also in choroider- Impaired cone performance in the dark-adapted state emia.11 Likewise, other agents capable of supporting pho- is the most plausible explanation for the symptom of poor toreceptor health in the absence of the RPE may also be night vision in the female carrier. Although abnormal suitable treatment strategies for choroideremia. Preclini- thresholds had been reported before,21 to our knowl- cal studies to test these mechanistic and therapeutic hy- edge, impaired dark-adapted cone-driven function in a potheses appear to be in order. choroideremia carrier documented across the visual field with monochromatic automated perimetry had not been Submitted for Publication: September 20, 2006; final re- previously reported. Cone dysfunction as the cause for vision received December 22, 2006; accepted January 19, nyctalopia has been documented,22 although in these cases 2007. it was due to anomalous rod-cone interactions to flick- Corresponding Author: Alessandro Iannaccone, MD, MS, ering stimuli in the dark-adapted state in the absence of Hamilton Eye Institute, University of Tennessee Health threshold abnormalities to static stimuli. Degenerate reti- Science Center, 930 Madison Ave, Ste 731, Memphis, TN nal cones in female carriers have been observed.23 How- 38163 ([email protected]). ever, to our knowledge, the molecular basis for cone dis- Financial Disclosure: None reported. ease in choroideremia carriers is unknown. Funding/Support: This study was supported in part by The differences that we observed between the af- a career development award (Dr Iannaccone) and an un- fected proband and the female carrier suggest that the restricted grant (Department of Ophthalmology, Uni-

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©2007 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/29/2021 versity of Tennessee Health Science Center) from Re- pes fixation: a contiguous gene deletion syndrome in Xq21. Am J Hum Genet. search to Prevent Blindness, Inc; by Foundation Fighting 1989;45(4):530-540. 16. Cremers FP, van de Pol DJ, Diergaarde PJ, et al. Physical fine mapping of the Blindness (Dr MacDonald); and by Foundation Fight- choroideremia locus using Xq21 deletions associated with complex syndromes. ing Blindness–Canada (Dr MacDonald). Genomics. 1989;4(1):41-46. Additional Contributions: Rashmi Pandya-Lipman, MD, 17. Rosenberg T, Niebuhr E, Yang HM, Parving A, Schwartz M. Choroideremia, con- referred this family for evaluation; Joe Mastellone, CRA, genital deafness and mental retardation in a family with an X chromosomal deletion. provided invaluable assistance with ophthalmic photog- Ophthalmic Paediatr Genet. 1987;8(3):139-143. 18. Nussbaum RL, Lesko JG, Lewis RA, Ledbetter SA, Ledbetter DH. Isolation of anony- raphy, optical coherence tomography, and digital image mous DNA sequences from within a submicroscopic X chromosomal deletion capture and processing; Mary Lane, BS, provided assis- in a patient with choroideremia, deafness, and mental retardation. Proc Natl Acad tance with clinical research coordination; and William Sci U S A. 1987;84(18):6521-6525. Andrew Todd, BS, provided technical assistance. We thank 19. Ayazi S. Choroideremia, obesity, and congenital deafness. Am J Ophthalmol. 1981; 92(1):63-69. the Le Bonheur pediatric anesthesiology team and nurs- 20. Cheng CK, Chen MS, Hou PK. Choroideremia: a study of two families. J Formos ing staff and all the family members who participated en- Med Assoc. 1991;90(11):1103-1112. thusiastically in this study. 21. Kurstjens JH. Choroideremia and gyrate atrophy of the choroid and retina. Doc Ophthalmol. 1965;19(1):2-122. doi:10.1007/BF00180759. 22. 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