Prevalence of Mutations Causing Retinitis Pigmentosa and Other Inherited Retinopathies

Abstract

Inherited retinopathies are a genetically and phenotypically heterogeneous group of diseases affecting approximately one in 2000 individuals worldwide. For the past 10 years, the Laboratory for Molecular Diagnosis of Inherited Eye Diseases (LMDIED) at the University of Texas-Houston Health Science Center has screened subjects ascertained in the United States and Canada for mutations in genes causing dominant and recessive autosomal retinopathies. A combination of single strand conformational analysis (SSCA) and direct sequencing of five genes (rhodopsin, peripherin/RDS, RP1, CRX, and AIPL1) identified the disease-causing mutation in approximately one-third of subjects with autosomal dominant retinitis pigmentosa (adRP) or with autosomal dominant cone-rod dystrophy (adCORD). In addition, the causative mutation was identified in 15% of subjects with Leber congenital amaurosis (LCA). Overall, we report identification of the causative mutation in 105 of 506 (21%) of unrelated subjects (probands) tested; we report five previously unreported mutations in rhodopsin, two in peripherin/RDS, and one previously unreported mutation in the cone-rod homeobox gene, CRX. Based on this large survey, the prevalence of disease-causing mutations in each of these genes within specific disease categories is estimated. These data are useful in estimating the frequency of specific mutations and in selecting individuals and families for mutation-specific studies.

INTRODUCTION

To date, over 120 loci for inherited retinal degeneration have been identified, and 56 of the associated genes have been cloned (RetNet, http://www.sph.uth.tmc.edu/RetNet/). Retinal disorders are also phenotypically heterogeneous, such that a single mutation may be associated with substantially different phenotypes within a family or between families, and different mutations within the same gene can cause substantially different retinal disorders. For example, mutations in one gene, peripherin/RDS (RDS; MIM# 179605), have been associated with several forms of inherited retinal degeneration, including cone-rod dystrophy, cone dystrophy, foveal dystrophy, and retinitis pigmentosa [Weleber et al., 1993; Wells et al., 1993; Keen et al., 1994; Nakazawa et al., 1994, 1996]. This clinical heterogeneity has made the molecular diagnosis of inherited eye diseases complicated; moreover, it has made identification of the underlying molecular cause of retinopathy within individual families an essential component of clinical research. If the gene defect causing the inherited retinopathy of a patient is identified, then prenatal diagnosis, a more accurate prognosis, and more accurate genetic counseling may be offered. In addition, several gene-specific and mutation-specific treatments for inherited retinal disorders have been proposed [Lewin et al., 1998; Frasson et al., 1999].

For the past decade, the Laboratory for Molecular Diagnosis of Inherited Eye Diseases (LMDIED, CLIA#45D0935007) at The University of Texas-Houston Health Science Center has tested over 500 unrelated subjects (probands) with inherited retinal disorders who were ascertained within Canada and the United States. The complete coding sequences of rhodopsin (RHO; MIM# 180380), peripherin/RDS, CRX (MIM# 602225), and AIPL1 (MIM# 604392) were assayed in all samples by SSCA, followed by sequencing of variants. In addition, because disease-causing mutations in the RP1 gene (MIM# 603937) appear to cluster in one region of exon 4 [Bowne et al., 1999], that region was assayed by SSCA in all patient samples, and all variants were sequenced. We report identification of the disease-causing mutation in roughly one-third of subjects with autosomal dominant retinitis pigmentosa (adRP) or with autosomal dominant cone-rod dystrophy (adCORD) (Table 1). In addition, mutations were identified in approximately 15% of subjects with Leber congenital amaurosis (LCA).

TABLE 1.

Summary of Probands Whose Causative Mutation Was Identified in This Study

Diagnosis	Mode of inheritance	Total tested	Rhodopsin	Peripherin/RDS	RP1	CRX	AIPL1
RPa	Autosomal dominant	206	53	17	8	2	0
	Isolated/recessive	138	2	0	0	0	0
	Unknownb	79	4	2	0	0	0
RD w/cone	Autosomal dominant	34	0	7	0	3	2
	Isolated/recessive	17	0	2	0	0	0
	Unknownb	15	0	0	0	0	0
LCA	Autosomal dominant	2	0	0	0	1	0
	Isolated/recessive	25	0	0	0	0	3

^aRP, retinitis pigmentosa; RD w/cone, retinal disorder with cone involvement; LCA, Leber congential amaurosis; CRX, cone-rod homeobox gene; AIPL1, aryl-hydrocarbon interacting protein-like 1.

^bFamily history unavailable.

MATERIALS AND METHODS

Subjects

Informed consent was obtained from all adult subjects, who were ascertained in the United States and Canada. Ethnicity of subjects could not be determined in most cases, as all samples were obtained under institutional rules of confidentiality. However, the population origin for these subjects is largely Caucasian of European ancestry. All tested individuals with disease-causing mutations received clinical evaluations by at least one of the co-authors, and in some instances, by two co-authors jointly.

DNA Isolation

DNA was isolated from peripheral blood using the Puregene DNA extraction kit (Gentra, Minneapolis, MN), in accordance with the manufacturer’s instructions. A working stock for mutation analysis was stored at 4°C, and the primary sample was stored separately at −70°C. All mutations identified by SSCA and direct sequencing of the working stock were confirmed by direct sequencing of the primary DNA sample.

SSCP Analysis

Genomic DNA samples from subjects were screened by SSCA, using published PCR primer sequences and conditions: rhodopsin [Daiger et al., 1997], peripherin/RDS [Daiger et al., 1997], CRX [Sohocki et al., 1998], RP1 [Bowne et al., 1999], and AIPL1 [Sohocki et al., 2000].

DNA Sequencing

After an SSCA variant was identified, a PCR reaction was performed under the same conditions as for SSCA. The amplified fragment was then treated with shrimp alkaline phosphatase and exonuclease I (USB, Cleveland, OH). Direct sequencing was performed with either the AmpliCycle sequencing kit (PE Biosystems) and a primer end-labeled with ³³P-ATP followed by autoradiography, or the BigDye Terminator Sequencing Kit (PE Biosystems) on an ABI Prism 310 automated sequencer according to the manufacturer’s protocols.

Peripherin/RDS Haplotype Identification

For haplotype identification of the peripherin/RDS exon 3 polymorphisms, DNA was amplified incorporating ³²P-dCTP with a biotinylated forward primer (5′-TTGGGCTGCTACCTACAG-3′) and an unbiotinylated reverse primer (5′-AGACTTTCGGAGTTGGATGAG-3′) and standard cycling conditions. Individual strands were separated with Dynabeads (DYNAL, Lake Success, NY) according to manufacturer’s protocols and were separated overnight on 0.4X MDE (Biowhittaker, Rock-land, ME) gels.

RESULTS

Likely disease-causing mutations were identified in 105 of the 506 total probands tested, or in approximately 21% of samples. The frequency of mutations identified in autosomal dominant retinopathies was considerably higher—approximately one-third of adRP and one-third of autosomal dominant retinal degeneration with cone involvement were explained by mutations identified in this study.

Retinitis Pigmentosa

Rhodopsin

Rhodopsin mutations were identified in 53 probands from 206 adRP families (26%), two from isolated probands with RP, and four from individuals with RP of unknown inheritance pattern (Table 2A). As expected, the Pro23His rhodopsin mutation was the most frequent, representing 41% of rhodopsin mutations and causing adRP in 22 of 206 (11%) of subjects. The second most common mutation was Arg135Trp, found in 5 (3%) of adRP families. In addition to published mutations, five previously unreported disease-causing rhodopsin mutations were identified, each confirmed by direct genomic sequencing in at least one independently collected DNA sample.

TABLE 2A.

Summary of Rhodopsin Mutations Identified in Families With Retinitis Pigmentosa (in Codon Order)

Diagnosis	Mutation/predicted consequence	Family identifier	cDNAa	Reference
ad RP	Pro23His	22 Familiesb	68C>A, CCC→CAC	Dryja et al. [1990]
ad RP	Leu46Arg	RFS004	137T>G, CTC→CGG	Rodriguez et al. [1993]
ad RP	Leu57Arg	UTAD070	170C>G, CCC→CGC	Inglehearn et al. [1992]
ad RP	Gly106Trp	UTAD013	316G>T, GGG→TGG	Sung et al. [1991]
ad RP	Gly106Arg	RFS072, RFS086	318A>G, GGA→GGG	Inglehearn et al. [1992]
ad RP	Cys110Phe	RFS036	329G>T, TGC→TTC	Fuchs et al. [1994]
ad RP	Arg135Trp	5 Familiesc	403C>T, CGG→TGG	Sung et al. [1991]
ad RP	Ala164Val	RFS163	491C>T, GCG→GTG	Fuchs et al. [1994]
ad RP	Pro170Arg	RFS153	509C>G, CCC→CGC	Present study
ad RP	Pro171Ser	RFS049	511C>T, CCA→TCA	Vatithinathan et al. [1994]
ad RP	Pro171Gln	UTAD096	512C>A, CCA→CAA	Antiñolo et al. [1994]
ad RP	Glu181Lys	UTAD089, UIC17	541G>A, GAG→AAG	Dryja et al. [1991]
ad RP	Cys185Arg	RFS075, RFS089	553T>C, TGC→CGC	Present study
ad RP	Asp190Asn	RFS003	568G>A, GAC→AAC	Keen et al. [1991]
ad RP	Met207Arg	TCDM	620T>G, ATG→AGG	Farrar et al. [1992]
ad RP	Pro210Leu	UTAD088	629C>T, CCT→CTT	Present study
ad RP	His211Arg	UTAD022	632A>G, CAC→CGC	Macke et al. [1993]
ad RP	Ser270Arg	UTAD042	C810A, AGC→AGA	Daiger et al. [1997]
ad RP	Lys296Asn	UTAD396	888G>T, AAG→AAT	Present study
ad RP	Frameshift after Glu332	UTAD072	995-1011del	Daiger et al. [1997]
ad RP	Pro347Ala	UTAD407	1039C>G, CCG→GCG	Stone et al. [1993]
ad RP	Pro347Leu	UTAD188, UTAD140	1040C>T, CCG→CTG	Dryja et al. [1990]
ad RP	Pro347Thr	UTAD081	1039C>A, CCG→ACG	Daiger et al. [1997]
RP, isolated	Pro180Ala	UTAD052	538C>G, CCC→GCC	Daiger et al. [1997]
RP, isolated	Leu318del	UTAD338	953-955del	Present study
RPd	Arg135Leu	UTAD264, UTAD332	404G>T, 405G>T, CGG→CTT	Sung et al. [1991]
RPd	Arg135Trp	RFS105	403C>T, CGG→TGG	Sung et al. [1991]
RP, sectorald	Thr17Met	RFS160	50C>T, ACG→ATG	Sheffield et al. [1991]

^acDNA sequence numbering, counting the first nucleotide of the first codon as 1. None of these mutations were identified in 50 unaffected control individuals.

^bBCMAD032, RFS001, RFS008, RFS010, RFS023, RFS025, RFS037, RFS069, RFS071, RFS136, RFS159, RFS162, UIC15, UTAD010, UTAD018, UTAD043, UTAD084, UTAD085, UTAD109, UTAD230, UTAD414, UTAD437.

^cRFS096, RP01B, UTAD120, UTAD159, UTAD163.

^dFamily history unavailable.

Pro170Arg

The Pro170Arg mutation segregated with RP in three affected individuals of RFS153, and was not observed in any of the other 1,000 chromosomes tested. This nonconservative substitution replaces the neutral, hydrophobic, rigid ring of proline with a large, basic arginine residue within the fourth transmembrane region of rhodopsin.

Cys185Arg

The Cys185Arg mutation segregated with the retinitis pigmentosa of two adRP families, RFS075 and RFS088, and was not observed in any other probands tested. The cysteine at this position is conserved in lamprey, chicken, bovine, and human rhodopsin [Okano et al., 1992].

Pro210Leu

A Pro210Leu mutation was identified in the affected proband of UTAD088 and was not observed in the other individuals tested. This mutation is nonconservative, substituting leucine for the rigid ring of proline at this position within the fifth transmembrane region of rhodopsin. As proline is known to be important in folding the peptide chain, this mutation is likely to alter the secondary structure of the protein.

Leu318del

A 3 base pair deletion was identified in an isolated individual with RP, UTAD338. The deletion alters amino acids 318 and 319, deleting the leucine at position 318, and causing the threonine at position 319 to be replaced by a proline. The threonine at position 319 is highly conserved in lamprey, chicken, bovine, and human rhodopsin [Okano et al., 1992].

Peripherin/RDS

Disease-causing mutations in peripherin/RDS were identified in approximately 8% (17 of 206) of the adRP probands. In addition, mutations were identified in two isolated RP cases (Table 2B). Two previously unreported mutations were also identified.

TABLE 2B.

Summary of Peripherin/RDS Mutations Identified in Families With Retinitis Pigmentosa

Diagnosis	Mutation/predicted consequence	Family identifier	cDNAa	Reference
ad RP	Arg46Ter	UTAD399	136C>T, CGA→TGA	Meins et al. [1993]
ad RP	Leu126Arg	UTAD280	377T>G, CTG→CGG	Kajiwara et al. [1992]
ad RP	Arg172Gln	UTAD396	516G>T, AAG→AAT	Wells et al. [1993]
ad RP	Leu185Pro	UTAD215	554T>C, CTG→CCG	Kajiwara et al. [1992]
ad RP	Val206-209del	UTAD023	616-627del	Keen et al. [1996]
ad RP	Pro210Arg	4 Familiesb	629C>G, CCT→CGT	Feist et al. [1994]
ad RP	Pro216Leu	RFS070, RFS058	647C>T, CCT→CTT	Kajiwara et al. [1992]
ad RP	Pro216Ser	UTAD095	646C>T, CCG→TCT	Fishman et al. [1994]
ad RP	Gly266Asp	UTAD056, UTAD058	797G>A, GGT→GAT	Kajiwara et al. [1992]
ad RP	IVS2+3 A>T	3 Familiesc	1068+3A→T	Sullivan et al. [1996]
RP vs. AFMD	Tyr141Cys	BCMAD033	422A>G, TAC→TGC	Present study
RPd	Gln178Arg	UTAD185	533A>G, CAG→CGG	Present study
RPd	Pro210Arg	UTAD313	629C>G, CCT→CGT	Feist et al. [1994]

^acDNA sequence numbering, counting the first nucleotide of the first codon as 1. None of these mutations were identified in 50 unaffected control individuals.

^bRFS079, RFS152, UTAD174, UTAD379.

^cRFS027, RFS055, RFS083.

^dFamily history unavailable.

Tyr141Cys

A Tyr141Cys mutation segregated with the retinitis pigmentosa in affected individuals of family BCMAD033 and in none of the other 1,000 chromosomes tested. The tyrosine at this position is conserved in human, bovine, and murine peripherin/rds [Connell et al., 1991].

Gln178Arg

The Gln178Arg mutation was observed only in the affected proband of family UTAD185. The glutamine at residue 178 of peripherin/RDS is conserved in human, bovine, and murine peripherin/rds [Connell et al., 1991].

RP1

The majority of disease-causing RP1 mutations detected to date cluster in a region of exon 4 [Bowne et al., 1999; Grimsby, 2000]; therefore, 150 of the probands were assayed by SSCA in this region only. The remaining 56 probands are of large adRP families and were tested for mutations in the complete RP1 gene by SSCA. Five previously reported RP1 mutations were identified by LMDIED in eight of the 206 adRP probands, or in about 4% of adRP tested (Table 2C).

TABLE 2C.

Summary of RP1 Mutations Identified in Families With Retinitis Pigmentosa

Diagnosis	Mutation/predicted consequence	Family identifier	cDNAa	Reference
ad RP	Arg677Ter	RFS137, UTAD103	2029C>T, CGA→TGA	Sullivan et al. [1999]; Pierce et al. [1999]; Bowne et al. [1999]
ad RP	Gly723Ter	UTAD411	2167G>T, GGA→TGA	Grimsby et al. [2000]
ad RP	Frameshift after Ile725	UTAD309	2169-2170insG	Bowne et al. [1999]
ad RP	Frameshift after Leu762	3 Familiesb	2285-2289del	Pierce et al. [1999]; Bowne et al. [1999]
ad RP	Frameshift after Gly723	RFS103	2303del	Bowne et al. [1999]

^acDNA sequence numbering, counting the first nucleotide of the first codon as 1. None of these mutations were identified in 50 unaffected control individuals.

^bUTAD029, UTAD039, UTAD351.

Cone-rod homeobox gene, CRX

CRX mutations were identified in two families diagnosed with adRP, RFS087, and UTAD341. The proband of RFS087 was heterozygous for the Arg41Gln mutation reported previously [Swain et al., 1997] in the proband of a family with autosomal dominant cone-rod dystrophy. Following identification of the mutation, detailed clinical evaluations in this and other family members indicated that the phenotype in RFS087 is more accurately described as a late-onset, slowly progressing, mild form of cone-rod dystrophy [Tzekov et al., 2000].

Another previously unreported mutation, Arg115Gln (G344A, CGG→CAG), was identified in the affected proband of UTAD341. This mutation was not identified in 50 normal control individuals or in any of the other 1,000 chromosomes tested. The arginine at this position is conserved among human, bovine, and murine Crx, and in human CRX and OTX-1, and OTX-2, two members of the same protein family [Chen et al., 1997]. Additional clinical evaluations are necessary to determine if the affected individuals of UTAD341 have a retinal degeneration phenotype similar to the family with the Arg41Gln mutation and to confirm the phenotype in the UTAD341 family as “retinitis pigmentosa.”

Retinal Disorders With Cone Involvement

The retinal disorders in this category include those with clinical diagnoses of cone-rod dystrophy, cone degeneration, macular degeneration, and Bardet-Biedl disease (Table 3). Six previously reported mutations were identified as the cause of retinal degeneration in 12 families whose retinal disorder included cone degeneration. No rhodopsin mutations were identified in this category.

TABLE 3.

Summary of Mutations Identified in Retinopathy Subjects With Cone Involvement

Mutation/predicted consequence	Diagnosis	Family identifier	cDNAa	Reference
RDS Arg172Trp	ad CDb, progressive	RFS139	514C>T, CGG→TGG	Wroblewski et al. [1994]
RDS Arg13Trp	Bardet Biedl	UTAD087	37C>T, CGG→TGG	Jacobson et al. [1995]
RDS Leu45Phe	CORD, isolated	UTAD064	133C>T, CTC→TTC	Jacobson et al. [1995]
RDS IVS2+3 A>T	ad MDc	Five familiesd	1068+3A→T	Sullivan et al. [1996]
CRX Glu80Ala	ad CORD	UTAD148, UTAD237	238A>C, GAG→GCG	Freund et al. [1997]
CRC Frameshift after Ala196	ad CORD	RFS014	585insC	Sohocki et al. [1998]
AIPL 1 Pro 351-354del	ad CORD	UTAD231, UTAD907	del1053-1064	Sohocki et al. [2000b]

^acDNA sequence numbering, counting the first nucleotide of the first codon as 1. These mutations were not present in 50 unaffected control individuals.

^badCORD, autosomal dominant cone-rod dystrophy; adCD, autosomal dominant cone degeneration; adMD, autosomal dominant macular degeneration.

^cMacular degeneration with peripheral involvement.

^dRFS091, RFS142, RFS156, RFS161, UTAD207.

Leber Congenital Amaurosis (LCA)

Homozygous or compound-heterozygous mutations were identified in three of 25 (~12%) probands with recessive or isolated LCA. In addition, a heterozygous CRX mutation was identified as the cause of autosomal dominant LCA in one family (Table 4). Therefore, the causative mutation was identified in approximately 15% (four of 27) of all subjects with a diagnosis of Leber congenital amaurosis.

TABLE 4.

Summary of Mutations Identified in Retinopathy Subjects With Leber Congenital Amaurosis

Mutation/predicted consequence	Diagnosis	Family identifier	cDNAa	Reference
AIPL1 Trp278Ter	LCA	RFS121	834G>A, TGG→TGA	Sohocki et al. [2000a]
AIPL1 Frameshift after Ala336		RFS121	1008-1009del	Sohocki et al. [2000a]
AIPL1 Trp278Ter	ar LCA	RFS127	834G>A, TGG→TGA	Sohocki et al. [2000a]
AIPL1 Cys239Arg	ar LCA	RFS128	717T>C, TGC→CGC	Sohocki et al. [2000a]
CRX Leu146-149del	ad LCA	RFS900	438-449del	Sohocki et al. [1998]

^acDNA sequence numbering, counting the first nucleotide of the first codon as 1. None of these mutations were identified in 50 unaffected control individuals.

Benign Variants

Several apparently benign coding sequence variants were identified in the current survey (Table 5). In addition, frequencies were determined for the haplotypes of peripherin/RDS codon 304/310/338 polymorphisms. The respective frequencies for the G/A/G, C/G/A, and C/ A/A haplotypes were 0.77, 0.09, and 0.13. Two unique haplotypes, C/A/G and G/A/A, were also identified in one individual each.

TABLE 5.

Apparently Benign Coding Sequence Variants in This Population

Gene	Variant	cDNA	Evidencea	Frequency
Rhodopsin	GLy120Gly	360C>T (GGC→GGT)	2	.02
	Thr160Thr	480C>T (ACC→ACA)	2	<.01
	Ala173Ala	519C>T (GCC→GCT)	2	<.01
	Ser186Ser	558G>A (TCG→TCA)	2	<.01
	Ser297Ser	891C>T (AGC→AGT)	2	<.01
Peripherin/RDS	Val106Val	318C>T (GTC→GTT)	2	.26
	Glu304Gln	910G>C (GAG→GCT)	3 Keen et al. [1996]	.23
	Lys310Arg	929A>G (AAG→AGG)	3 Keen et al. [1996]	.10
	Gly336Gly	1008C>T (GGC→GGT)	2	<.01
	Gly338Asp	1014G>A (GGC→GAC)	3 Keen et al. [1996]	.22
RP1	Arg872His	2615G>A (CGT→CAT)	3 Sullivan et al. [1999]	.25
	Asn985Tyr	2953A>T (AAT→TAT)	3 Sullivan et al. [1999]	.46
	Arg1595Gln	4784G>A (CGG→CAG)	1	<.01
	Ala1670Thr	5008G>A (GCA→ACA)	3 Sullivan et al. [1999]	.22
	Ser1691Pro	5071T>C (TCT→CCT)	3 Sullivan et al. [1999]	.23
	Gln1725Gln	5175A>G (CAA→CAG)	3 Sullivan et al. [1999]	.20
	Cys2033Tyr	6098A>G (TAT→TGT)	3 Sullivan et al. [1999]	.46
	Leu808Pro	5423T>C (CTG→CCG)	1	.01
	Ile2122Ile	6366T>C (ATT→ATC)	2	<.01
CRX	His10Asp	28C>T (CAC→GAC)	2	<.01
	Val66Ile	196G>A (GTC→ATC)	1	<.01
	Gly122Asp	365G>A (GGC→GAC)	4	<.01
	Ala158Thr	472G>A (GCC→ACC)	3 Swain et al. [1997]	<.01
	Gly183Gly	538G>A (GGG→GGA)	2	<.01
	Ser199Ser	596C>T (TCC→TCT)	1	<.01
AIPL1	Phe37Phe	111T>C (TTT→TTC)	2	.02
	Ser78Ser	234C>T (TCC→TCT)	2	<.01
	Cys89Cys	287C>T (TGC→TGT)	2	.01
	Asp90His	268G>C (GAC→CAC)	1	.16
	Leu100Leu	300G>A (CTG→CTA)	2	.43
	His172His	516T>C (CAT→CAC)	2	<.01
	Pro217Pro	651G>A (CCG→CCA)	2	.39
	Asp255Asp	765T>C (GAT→GAC)	2	<.01

^aEvidence that variant is benign: 1 = does not segregate with retinal disorder in one or more families; 2 = Silent substitution; 3 = published reference; 4 = variance identified in unaffected controls.

DISCUSSION

The purpose of this project was to determine the prevalence of disease-causing mutations in five genes known to cause inherited retinopathy: rhodopsin, peripherin/RDS, RP1, CRX, and AIPL1. Mutation testing was performed in over 500 subjects in the broad diagnostic categories of either retinitis pigmentosa without apparent cone involvement or retinal degeneration with cone involvement. Patients were further classified by mode of inheritance and detailed clinical findings. Patients in the study were from families ascertained in the United States or Canada. In addition to providing useful clinical information for the patients and families involved in the study, mutation screening in this population offers several further benefits. First, this survey permits estimation of the relative prevalences (relative to each disease category) for mutations within each gene and for each observed mutation. This information is useful in determining the gene-specific and mutation-specific diagnostic and treatment needs within this population. Second, we report eight novel disease-causing mutations which contribute to the overall allelic variability at these loci. Third, we report several benign sequence variants within these genes, and their respective frequencies. These data will assist other diagnostic laboratories in distinguishing disease-causing mutations from benign variants. Finally, families and patients with specific mutations, identified in this study by confidential numbers, may be available for further study. Access to these subjects, with appropriate consent and maintenance of confidentiality, is available through the clinicians participating in the survey.

These data reinforce the heterogeneity of inherited retinopathies and the need for molecular diagnostics. For example, a single peripherin/RDS splice-site mutation, IVS2+3A>T, was identified as the cause of retinopathy in eight families; the phenotype in these families ranges from retinitis pigmentosa to macular degeneration. Further, although our assays may have missed some mutations, our data indicate that the inherited retinal degeneration genes that were not screened or have not yet been identified may account for approximately two-thirds of inherited retinopathy in these diagnostic categories. The combination of the heterogeneity of inherited retinal disorders and the developing studies involving gene-specific or mutation-specific treatments for these disorders makes identification of the remaining genes and accurate molecular diagnosis of these disorders even more important.