Association of a Novel Mutation in the Retinol Dehydrogenase 12 (RDH12) Gene with Autosomal Dominant Retinitis Pigmentosa

OPHTHALMIC MOLECULAR GENETICS

SECTION EDITOR: JANEY L. WIGGS, MD, PhD Association of a Novel Mutation in the Retinol Dehydrogenase 12 (RDH12) Gene With Autosomal Dominant Retinitis Pigmentosa

John H. Fingert, MD, PhD; Kean Oh, MD; Mina Chung, MD; Todd E. Scheetz, PhD; Jeaneen L. Andorf, BS; Rebecca M. Johnson, BS; Val C. Sheffield, MD, PhD; Edwin M. Stone, MD, PhD

Objective: To identify the gene causing retinitis pig- gene. A frameshift mutation (776delG) was detected in mentosa (RP) in an autosomal dominant pedigree. all affected family members and was not detected in 158 control subjects. Methods: Family members with RP were studied with linkage analysis using single-nucleotide polymorphism Conclusions: Heterozygous mutations in RDH12 can and short tandem repeat polymorphic markers. Candi- cause autosomal dominant RP with a late onset and rela- date genes in the linked region were evaluated with DNA tively mild severity. This phenotype is dramatically dif- sequencing. ferent from the other disease associated with mutation in this gene, autosomal recessive Leber congenital Results: Nineteen family members had a mild form of amaurosis. RP. Multipoint linkage analysis of single-nucleotide polymorphism genotypes yielded a maximum nonparamet- Clinical Relevance: The demonstration that muta- ric linkage score of 19.97 with markers located on chro- tions in a gene previously associated with recessive Leber mosome 14q. LOD scores higher than 3.0 were obtained congenital amaurosis can also cause dominant RP illus- with 20 short tandem repeat polymorphic markers, and trates the wide phenotypic variability of retinal degen- recombinants defined a 21.7-centimorgan locus on chro- eration genes. mosome 14q. The retinol dehydrogenase 12 (RDH12) gene lies within this locus and was evaluated as a candidate Arch Ophthalmol. 2008;126(9):1301-1307

ETINITIS PIGMENTOSA (RP) IS .sph.uth.tmc.edu/Retnet/). The 14 known a collection of inherited, ADRP genes are CA4,4,5 CRX,6,7 FSCN2,8 progressive retinal degen- GUCA1B,9 IMPDH1,10-12 NR2E3,13 NRL,14 erations of the photorecep- PRPF3,15,16 PRPF8,17,18 PRPF31,19,20 RDS,21,22 tors with typical clinical RHO,23-26 ROM1,27 RP1,28-31 RP9,32,33 and featuresR including attenuated retinal ar- SEMA4A.34 These genes have a range of terioles, intraretinal bone spiculelike pig- functions, including phototransduction mentation, and posterior subcapsular cata- (RHO); RNA splicing (PRPF3, PRPF8, ract. Retinitis pigmentosa is characterized PRPF9, and PRPF31); signaling (SEMA4A); by marked reduction of both rod and cone and retinal structure (RDS/peripherin, responses in the electroretinogram, pe- FSCN2, and RP1). Mutations associated Author Affiliations: Departments of Ophthalmology ripheral visual field defects, and reduc- with ADRP are most commonly detected and Visual Sciences tion of central vision later in the course in rhodopsin (RHO), RDS/peripherin, and (Drs Fingert, Scheetz, and of the disease. The prevalence of RP is ap- PPRF31, which account for approxi- Stone, and Mss Andorf and proximately 1 in 4000 and more than 1 mately 25%, 10%, and 8% of ADRP, re- Johnson) and Pediatrics million individuals may be affected with spectively. The other genes are associated (Dr Sheffield), Carver College RP worldwide.1 with smaller fractions of disease.35 Over- of Medicine, University of Iowa, Details of the genetic features of RP have all, mutations in these known disease- and the Howard Hughes been recently reviewed.1-3 Retinitis pigmen- causing genes can be detected in nearly half Medical Institute (Drs Sheffield tosa may have an autosomal dominant of all ADRP cases, which suggests that many and Stone), Iowa City; (30%-40%), autosomal recessive (50%- more ADRP genes remain to be identified. Associated Retinal Consultants, 60%), or X-linked (5%-15%) inheritance There is considerable overlap be- Traverse City, Michigan 1 (Dr Oh); and Department of pattern. At present, 16 genetic loci for au- tween the inheritance patterns and the spe- Ophthalmology, University of tosomal dominant RP (ADRP) have been cific types of retinal dystrophies that are Rochester, Rochester, NY identified and the genes at 14 of the loci associated with mutations in a particular (Dr Chung). have been discovered (RetNet: http://www gene. For example, mutations in RHO,

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©2008 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/27/2021 NRL, and RP1 were initially associated with dominantly ously identified ADRP genes including rhodopsin (OMIM inherited RP,14,23-26,28-31 while different sets of mutations 180380), RDS/peripherin (OMIM 179605), and RP1 (OMIM in these same genes were later shown to cause autoso- 603937). Genotyping with STRP genetic markers was con- 47 mal recessive RP.36-38 Similarly, some of the same genes ducted using standard methods as previously described. A that cause ADRP (CRX, IMPDH1, RDS, RHO, and genome-wide scan was next performed with Affymetrix microarrays (Sty1 array of the GeneChip Human Mapping SEMA4A) have also been associated with a number of 500K Array Set, Affymetrix, Santa Clara, California), which other retinal phenotypes, including pattern dystrophy, interrogated 238 000 single-nucleotide polymorphisms Leber congenital amaurosis, cone dystrophy, and con- (SNPs). Sample processing and labeling were performed using genital stationary night blindness.39-42 Consequently, genes the manufacturer’s instructions. The arrays were hybridized, known to cause one retinal dystrophy are excellent can- washed, and scanned in the University of Iowa DNA core didates for causing others. facility. Array images were processed with GeneChip DNA In this study, we report the genetic analysis of a 6-gen- Analysis software. eration family from North Carolina with ADRP. The gene Microarray data were analyzed and multipoint nonpara- that causes ADRP in this family was mapped to chromo- metric linkage scores were calculated using the Genespring GT some 14q with linkage studies and recombination analy- software package (Agilent Technologies, Palo Alto, Califor- nia). Pairwise linkage analysis using STRP markers was per- sis. Family members were tested for disease-causing mu- formed with the MLINK and LODSCORE programs as imple- tations in candidate genes contained within this new mented in the FASTLINK (v2.3) version48,49 of the LINKAGE ADRP locus. A novel mutation in the retinol dehydro- software package.50 Penetrance and disease gene frequency were genase 12 (RDH12) gene was detected that cosegregates set to 99% and 0.1%, respectively. For each STRP marker, the with ADRP in this large pedigree. Mutations in RDH12 allele frequencies were assumed to be equal. True allele fre- have been previously associated with recessively inher- quencies could not be reliably estimated from the small num- ited retinal dystrophies described clinically as early- ber of spouses in the pedigree. To show that the assumption of onset retinal degeneration or Leber congenital amauro- the equal allele frequencies would not significantly affect our sis.43-45 However, this study presents the first case, to our linkage results, we recalculated the LOD scores using allele fre- knowledge, of ADRP associated with mutations in RDH12. quencies for the “affected” allele of the most tightly linked marker (D14S587) ranging from 0.01 to 0.5. The Zmax for D14S587 was 4.5 when the affected allele frequency was arbitrarily set METHODS to 50%. In the 10 spouses who were studied, the actual frequencies of the affected alleles of D14S587 were much lower The research study was approved by the internal review board than 50%. In this small sample, the frequency of the affected of the University of Iowa and informed consent was obtained allele of D14S587 was 10%, which provides additional evi- from study participants. dence that our use of equal allele frequencies for D14S587 (11%) was reasonable. PATIENT RESOURCES CANDIDATE ADRP Family GENE SCREENING

Thirty-five family members had complete eye examinations and Candidate genes were selected from among the genes in the chro- 19 were judged to have ADRP. Visual fields were assessed with mosome 14q–linked interval based on their function, expres- Goldmann perimetry and ISCEV standard electroretinograms sion pattern, and prior association with retinal disease. DNA were obtained from a subset of family members. Patients were samples from 2 affected family members and from 2 healthy judged to be affected if they had classic signs of RP, including control subjects were tested for mutations in candidate genes bone spiculelike pigmentation of the retina, attenuation of reti- using bidirectional sequencing of polymerase chain reaction nal arterioles, waxy pallor of the optic nerve, characteristic ring products that encompassed the entire coding sequence. The first, scotomas, and attenuated electroretinograms. and only, candidate to be evaluated was retinol dehydrogenase 12 (RDH12, OMIM 608830). Sequencing was performed Cohort of Patients With Photoreceptor using dye-terminator chemistry on an ABI 3730 DNA se- Degeneration and Controls quencer (Applied Biosystems, Foster City, California). Poly- merase chain reaction amplification was performed with a stan- 51 All patients (n=273) and healthy control subjects (n=158) were dard protocol using primer sequences that are available on ascertained from the same outpatient ophthalmology clinic popu- request. Potential mutations were identified by comparing the lation at the University of Iowa. Subjects underwent complete eye DNA sequence of the affected family members and healthy con- examinations and were judged to be affected if they exhibited signs trol subjects. Similarly, the DNA sequences of the affected fam- of a primary photoreceptor degeneration, including bone spic- ily members were compared with National Center for Biotech- ulelike pigmentation of the retina, reduced ISCEV standard elec- nology Information reference sequences (RDH12, NM_152443). Identified sequence variations were evaluated as potential dis- troretinogram amplitudes, and characteristic visual field defects. 52 Control subjects had no clinical signs or family history of a reti- ease-causing mutations using standard criteria. A single- nal degeneration. Blood samples were obtained from study par- strand conformation polymorphism (SSCP) assay was devel- ticipants and DNA was prepared using a nonorganic method.46 oped to detect the 776delG mutation in the control population (n=158) with a standard protocol51 using primer sequences that are available on request. The cohort of 273 patients with pri- LINKAGE STUDIES mary photoreceptor degenerations and 90 of the 158 healthy control subjects were tested for mutations in the entire RDH12 Pedigree members were first genotyped with short tandem gene using a combination of SSCP analysis and bidirectional repeat polymorphism (STRP) genetic markers flanking previ- sequencing using standard protocols.51

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II 12 34 56

III 12 34 5 6 78 910

IV 12 34 567891011 12 13 14 15 16 17 18 19 20 21 22 23

V 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

VI 1 2

Figure 1. Pedigree affected with autosomal dominant retinitis pigmentosa. Individuals found to be clinically affected with autosomal dominant retinitis pigmentosa are represented by black symbols while unaffected individuals or individuals with unknown affection status are depicted with open symbols. Individuals who are deceased are marked with a slash. Affected family members who were enrolled in the genetic study are indicated with an X. Circles represent females and squares represent males.

STATISTICS

The frequency of RDH12 variations detected in our cohort of patients with photoreceptor degeneration and our cohort of healthy control subjects was compared using the Fisher exact test for rare variants and ␹2 analysis for common variations. A 2-tailed P value Ͻ.05 was considered statistically significant.

RESULTS

CLINICAL STUDIES

Members of a 6-generation family (pedigree 041D) received complete eye examinations and 19 family members were found to be clinically affected with RP. The disease in this family demonstrated an autosomal dominant mode of transmission through several generations (Figure 1). Family members had retinal findings typical of RP, including intraretinal bone spiculelike pig- Figure 2. Fundus photograph of patient IV-6 at 62 years of age, mentation and attenuation of retinal arterioles (Figure 2). demonstrating bone spiculelike pigmentation and attenuation of retinal arterioles characteristic of retinitis pigmentosa. The retinal pigment Clinical information about the onset of disease was avail- epithelium in the periphery and surrounding the optic disk is also atrophic. able from 4 of the affected family members. The average age at diagnosis in these family members was 28.5 years (range, 12-43 years). Some affected family members have several loci containing genes already associated with maintained excellent central visual acuity (ie, 20/25 OU) ADRP was excluded (data not shown), a genome-wide and driving privileges into their eighth decade of life. scan for linkage was conducted by genotyping DNA samples from 8 of the affected family members with GENETIC STUDIES microarrays of SNPs. Analysis of the SNP data identified a region of chromosome 14q with a maximum DNA samples from the family, including 19 affected nonparametric multipoint linkage score of 19.97. All 8 members, were subsequently studied with linkage affected pedigree members were found to share an analysis using a stepwise approach. After linkage to allele of each of the 1350 consecutive SNPs that span

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©2008 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/27/2021 Recombinants Marshfield Marker Physical Position, bp Zmax Patient II-3 or Map, cM Patient IV-1 Patient IV-8 Patient III-10∗ D14S978 50 982 870 - 50 983 099 53.19 1.99 (θ = 0.088) D14S1018 51 563 972 - 51 564 176 55.29 1.70 (θ = 0.093) D14S989 52 774 794 - 52 774 972 55.29 5.07 (θ = 0) D14S139 53 039 214 - 53 039 459 55.82 6.44 (θ = 0) D14S587 53 436 576 - 53 436 854 55.82 6.81 (θ = 0) D14S747 53 637 396 - 53 637 596 55.82 5.17 (θ = 0) D14S991 54 293 775 - 54 293 933 55.82 3.34 (θ = 0) D14S1057 54 437 224 - 54 437 382 55.82 5.16 (θ = 0) D14S745 55 621 435 - 55 621 550 57.43 3.47 (θ = 0.043) D14S1056 55 718 215 - 55 718 408 57.98 5.88 (θ = 0) D14S285 56 044 222 - 56 044 335 59.43 6.15 (θ = 0) D14S980 56 222 320 - 56 222 479 60.43 5.31 (θ = 0) D14S274 56 729 297 - 56 729 420 63.25 2.87 (θ = 0) D14S1038 58 693 080 - 58 693 300 66.81 4.55 (θ = 0) D14S994 59 754 445 - 59 754 668 66.81 5.51 (θ = 0) D14S1429 59 967 990 - 59 968 174 66.81 4.52 (θ = 0) D14S592 60 466 609 - 60 466 835 66.81 4.08 (θ = 0) D14S997 61 770 246 - 61 770 457 67.99 3.92 (θ = 0) D14S1012 62 892 131 - 62 892 418 68.59 3.20 (θ = 0) D14S271 64 203 058 - 64 203 289 69.18 5.74 (θ = 0) D14S1046 64 252 866 - 64 253 080 69.82 3.81 (θ = 0.04) RDH12 67 258 943 - 67 270 921 D14S1069 67 457 943 - 67 458 158 73.03 2.78 (θ = 0) D14S125 65 447 777 - 65 447 977 74.01 2.86 (θ = 0) D14S1011 68 635 668 - 68 635 852 74.96 4.77 (θ = 0) D14S251 70 195 334 - 70 195 652 76.95 1.97 (θ = 0.06) D14S1002 70 370 762 - 70 370 929 78.4 4.45 (θ = 0.037)

Figure 3. Two-point linkage data and analysis of recombinant individuals. Twenty-six genetic markers from the long arm of chromosome 14 are listed on the left of the Figure, with the most centromeric marker at the top. The physical position of the short tandem repeat polymorphic markers is based on NCBI Build 36.1 of the human genome (National Center for Biotechnology Information, Bethesda, Maryland) and the genetic position of the markers is based on the Marshfield map (http://www.ncbi.nlm.nih.gov/mapview/). The maximum LOD score (Zmax) is given for each marker as well as the recombination frequency at which the Zmax occurred. The patient designations correspond to those in Figure 1. A black box indicates that during the meiosis that gave rise to the individual (*or that individual’s ancestor), an informative recombination event occurred between the marker and the disease gene. Uninformative meioses are indicated with gray boxes. The recombination events summarized in this Figure suggest that the disease-causing mutations lie within the 21.7-centimorgan (cM) (18.6–mega base pair [Mbp]) interval bounded by D14S1018 and D14S251. Because no fully informative meioses were detected between markers D14S1018 and D14S251, it was not possible to determine which side of this interval was narrowed by the recombination event observed in patient IV-1 at marker D14S745.

15.2 mega base pairs (Mbp) between rs4901408 and the retina53 and has an important role in the visual rs4902610. cycle.44,45 Mutations in this gene have been previously as- The chromosome 14q linkage was confirmed by geno- sociated with autosomal recessive retinal dystrophies in- typing all 19 affected pedigree members with 26 STRP cluding Leber congenital amaurosis43 and early-onset reti- markers in this region (Figure 3). Two-point paramet- nal dystrophy,44,45 which share some clinical features of ric LOD scores higher than 3.0 were obtained from 20 RP. Consequently, RDH12 was the first candidate gene STRP markers and a maximum LOD score of 6.81 (␪=0) to be evaluated. was obtained with marker D14S587. The analysis of pa- Two family members with RP were tested for disease- tients with recombination events near the linked inter- causing mutations in the coding sequence of RDH12 using val is also shown in Figure 3. These recombination events a DNA sequencing-based assay. A total of 3 DNA se- indicate that the disease-causing gene lies within the 21.7- quence variations were detected. Two variations are lo- centimorgan (18.6-Mbp) interval between markers cated within intervening sequences and are benign poly- D14S1018 (telomeric) and D14S251(telomeric). This morphisms, while one variation causes a change in the chromosome 14q locus contains 173 known genes. predicted protein sequence encoded by RDH12. A het- One of the top candidate genes in the chromosome erozygous deletion was detected at position 2 of codon 14q locus is retinol dehydrogenase 12 (RDH12). RDH12 259 (776delG), which causes a frameshift mutation and is predominantly expressed in the photoreceptor cells of a premature termination at codon 277. The 776delG mu-

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Homo sapiens 256 KTAREGAQTSLHCALAEGLEPLSGKYFSDCKRTWVSPRARNNKTAERLWNVSCELLGIRWE 316 Macaca mulatta 256 KTAREGAQTSLHCALAEGLEPLSGKYFSDCKRTWVSPRARNNKTAERLWNVSCELLGIRWE 316 Mus musculus 256 KSTSQGAQTSLHCALAEDLEPLSGKYFSDCKRMWVSSRARNKKTAERLWNVSCELLGIQWE 316 Rattus norvegic 355 KSPWQGAQTSLHCALEEGLEPLSGKYFSDCKRTWVSPRARNKKTAERLWNVSCELLGIQWE 415 Gallus gallus 266 KTPWEGAQTSVYCAVAEELESVTGQYFSDCQPAYVSPWGRDDETAKKLWNVSCELLGIQWD 326 Danio rerio 259 KSPKEGAQTSIYCAVAEELQSISGKHFSDCAPAFVAPQGRSEETARKLWDVSCELLGIEWD 319 Drosophila melanogaster 266 KTARNGAQTTLYAALDPSLEKVSGRYFSDCKQKHVGSAAQYDDDAQFLWAESEKWTGINI 325

Figure 4. Alignment of the terminal amino acid sequences encoded by human RDH12 and orthologous genes. The terminal 61 amino acids of human RDH12 protein are aligned with proteins encoded by orthologous genes. Amino acid sequences that are identical to the corresponding human sequences are highlighted gray. The mutation detected in our pedigree (776delG) causes a frameshift mutation in the arginine amino acid at position 259 that alters 17 amino acids and causes premature termination at codon 277.

Table. RDH12 Variations

No. (%)

Patients With Primary Photoreceptor Degeneration Healthy Controls Blosum P RDH12 Variation (n=273) (n=90) Score Value IVS2 −31 bp A-ϾG 1 (0.37) Heterozygous 0 NA Ͼ.99 IVS2 −20 bp insT 6 (2.2) Heterozygous 1 (1.1) Heterozygous NA Ͼ.99 Leu144Val 1 (0.37) Heterozygous 0 ϩ1 Ͼ.99 Ala126Glu 1 (0.37) Heterozygous 0 −1 Ͼ.99 Arg161Gln (rs17852293) 218 (80) Homozygous 70 (78) Homozygous 52 (19) Heterozygous 19 (21) Heterozygous ϩ1 .91 3 (1.1) Homozygous 1 (1.1) Homozygous Arg193Arg 0 1 (1.1) Heterozygous ϩ5 .25 Glu260Aspa 1 (0.37) Heterozygous 0 ϩ2 Ͼ.99

Abbreviations: bp, base pair; NA, not applicable. a The Glu260Asp variation was not coinherited with disease within a small pedigree.

tation was subsequently detected in all affected family tient harboring the Glu260Asp variation had affected fam- members and was absent from 158 control subjects. ily members available for study. However, the Glu260Asp The conservation of the RDH12 protein sequence was variation was not coinherited with disease in this family examined to provide support for the pathogenicity of the (data not shown), suggesting that this variation is a be- 776delG mutation. Comparison with other homolo- nign polymorphism. Analysis of conservation of protein se- gous genes suggests that amino acids 37 to 240 are re- quence was conducted using the blosum62 matrix.52,55 Some 54 sponsible for the dehydrogenase activity of RDH12. The amino acid substitutions are tolerated without harm to pro- 776delG mutation does not directly alter the dehydro- tein function better than others. The blosum62 matrix was genase functional domain; however, it alters or elimi- used to estimate the effects of the 4 nonsynonymous varia- nates the terminal 57 amino acids of RDH12, which are tions on the function of RDH12. Three of the 4 variations highly conserved (Figure 4). (Leu144Val, Arg161Gln, and Glu260Asp) cause changes To assess the role of RDH12 in the pathogenesis of RP, in the amino acid sequence predicted by RDH12 that are we screened a panel of 273 patients with primary pho- well tolerated by evolution, which is not indicative of dis- toreceptor degenerations and 90 ethnically matched controls for disease-causing mutations using a combination ease-causing mutations. One variation (Ala126Glu) causes of SSCP analysis and DNA sequencing. Patients were un- an amino acid substitution that is mildly supported by the selected for family history or for inheritance pattern of blosum62 matrix as a disease-causing mutation. Finally, disease; however, patients with a diagnosis of Leber con- statistical analysis of these variations either individually or genital amaurosis were excluded from this cohort. A total as a group failed to detect an association between the varia- of 7 different RDH12 variations were detected. Two variations and disease (Table). One commonly detected variations were detected within intervening sequences, 1 variation (Arg161Gln) was observed at the same frequency in tion was a synonymous codon change, and 4 variations patients and controls (P value=.91). This variation was simi- were nonsynonymous codon changes (Table). larly reported as a benign polymorphism in prior studies Multiple analyses were used to assess whether the 4 non- of RDH12.56 The other 3 nonsynonymous variations synonymous coding sequence variations detected in RDH12 (Leu144Val, Ala126Glu, and Glu260Asp) were each de- were likely to be pathogenic. Analysis of coinheritance with tected only once in the cohort of patients and were not sta- disease was possible for the Glu260Asp variation. The pa- tistically associated with disease (P value=Ͼ.99).

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©2008 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/27/2021 COMMENT that some of these RDH12 mutations significantly reduce the enzymatic activity of the encoded protein,44,56 which implies that autosomal recessive retinal dystrophies and se- Fourteen genes associated with ADRP have been discov- vere visual impairment are caused by loss of function mu- ered, and in this article, we report the identification of tations in RDH12. The 776delG mutation identified in our another disease-causing gene using positional cloning and ADRP family is likely to cause disease via a mechanism that candidate gene screening techniques. Linkage studies of is different than that previously reported for RDH12 mu- a large multiplex pedigree revealed a novel ADRP locus tations. This heterozygous mutation likely causes milder on chromosome 14q, which contains 173 known genes, disease via a gain of function or dominant negative mecha- including RDH12. nism rather than loss of function. Some RDH12 mutations RDH12 was considered the top candidate gene for caus- cause severe and early-onset retinal dystrophy when 2 alleles ing ADRP in the chromosome 14q locus because of its func- are inherited, while a single 776delG allele is capable of caus- tion, expression pattern, and prior association with other ing a mild, late-onset form of disease. Truncating muta- retinal dystrophies. RDH12 is predominantly expressed in tions, similar to 776delG, have been detected in each of the neurosensory retina57 and has an essential role in the RDH12’s 7 exons. However, only the 776delG mutation has conversion of all-trans retinal to all-trans retinol,44 which been associated with RP in the heterozygous state. Thus, is an essential step in the visual cycle. Autosomal reces- the different behavior of these mutations does not appear sive mutations in RDH12 have been associated with pro- to be due to their gross position within the RDH12 gene. found photoreceptor dysfunction and reduced visual func- Further study of the mechanism by which the 776delG mu- tion that is diagnosed at birth or in the first decade of life.43,44 tation causes disease may clarify the basis of RDH12 geno- Consequently, RDH12 was the first gene we evaluated as type-phenotype correlations as well as provide valuable in- the cause of RP in our pedigree. sight into the biology of the visual cycle and vision. Testing the family members for RDH12 variations revealed a frameshift mutation (776delG) that causes premature termination of the translation of the RDH12 tran- Submitted for Publication: August 13, 2007; final revi- script. Several lines of evidence suggest that this mutation sion received January 24, 2008; accepted January 29, 2008. causes ADRP in our family. First, the 776delG mutation Correspondence: Edwin M. Stone, MD, PhD, Depart- cosegregates with disease in the family. Second, this mu- ment of Ophthalmology, The University of Iowa Carver tation was not detected among 158 control subjects. Third, College of Medicine, Iowa City, IA 52242 (edwin-stone the 776delG mutation causes a truncation of the en- @uiowa.edu). coded RDH12 protein eliminating 57 amino acids from Financial Disclosure: None reported. the conserved carboxy terminus. This mutation signifi- Funding/Support: This work was supported by the Foun- cantly alters the structure of the RDH12 protein and is dation Fighting Blindness, Research to Prevent Blind- likely to impair its function. Finally, mutations in RDH12 ness, and the Grousbeck Family Foundation. Dr Fingert have been previously associated with retinal degenera- is supported by a Research to Prevent Blindness Career tions. Taken together, these data strongly suggest that Development Award. the 776delG mutation in RDH12 causes ADRP in our pedigree. Functional studies of the 776delG mutation would REFERENCES be helpful to further establish its mechanism of action. We additionally tested a large cohort of patients with 1. Hartong DT, Berson EL, Dryja TP. Retinitis pigmentosa. Lancet. 2006;368(9549): primary retinal degenerations for disease-causing muta- 1795-1809. 2. Bok D. Contributions of genetics to our understanding of inherited monogenic tions in RDH12. No additional instances of the del776C retinal diseases and age-related macular degeneration. Arch Ophthalmol. 2007; mutation were detected; however, 3 other RDH12 varia- 125(2):160-164. tions (Leu144Val, Ala126Glu, and Glu260Asp) were each 3. Daiger SP, Bowne SJ, Sullivan LS. Perspective on genes and mutations causing detected once in our cohort of patients. These varia- retinitis pigmentosa. 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