Purpose

To describe a patient with retinitis punctata albescens (RPA) associated with compound heterozygosity for two novel mutations in the RLBP1 encoding cellular retinaldehyde-binding protein (CRALBP).

Design

Observational case report.

Methods

The proband underwent a complete ophthalmic examination and leukocyte genomic DNA samples were obtained from him and his parents. The RLBP1 exons were analyzed by direct sequencing of PCR-amplified fragments.

Results

The patient had a clinical phenotype suggestive of slowly progressive RPA, characterized by numerous yellow-white dots in the fundus. The RLBP1 sequence analysis revealed a novel compound heterozygotic mutation of Gly145Asp and Ile200Thr transmitted from the mother and father, respectively. Analysis of 100 control chromosomes showed no individuals with these sequence alterations.

Conclusions

Only eight RLBP1 mutations have been reported to date, and here we describe two novel mutations. These additional mutations will aid ongoing functional studies and add to our understanding of the molecular pathology pertaining to RLBP1-associated retinopathies.

Multiple genome-wide scans involving sib-pairs or limited pedigrees have been extensively used for a wide number of complex genetic conditions. Comparing data from two or more scans, as well as combining data, require an understanding of the sources of genotyping errors and data discrepancies. We have conducted two genome-wide scans for age-related maculopathy using the Center for Inherited Disease Research (CIDR) and the Mammalian Genotyping Service (MGS). Thirty individuals were typed in common, in order to allow for the alignment of alleles and comparison of the data sets. The analysis of these 8914 genotypes distributed over 321 markers in common demonstrated excellent agreement between these two laboratories, which have low rates of internal errors. Under the assumption that within each genotype, the smaller MGS allele should correspond to the smaller CIDR allele, the alleles align well between the two centers, with only a small fraction (less than 0.65%) of the aligned alleles showing large differences in sizes. However, since called allele sizes are integer "labels" which may not directly reflect the true underlying allele sizes, it is important to carefully prepare in advance if one wishes to merge data from different laboratories. In particular, it would not suffice to attempt to align alleles by typing only one or two controls in common. Fortunately, for the purposes of linkage analysis, one can avoid merging difficulties by simply carrying out linkage analyses using laboratory-specific allele labels and allele frequencies for each laboratory-specific subset of the data.

Purpose

To describe the ophthalmic and genetic findings in a family with X-linked retinitis pigmentosa (RP) and Coats'-like exudative vasculopathy.

Design

Observational case series.

Methods

Family members underwent comprehensive ophthalmologic examination. Leukocyte genomic DNA samples were obtained and screened for RPGR (RP3) mutations by direct polymerase chain reaction sequencing.

Results

The proband had RP with bilateral Coats'-like vasculopathy and was treated with fluorescein-potentiated argon laser therapy. The findings in two other affected male patients and three obligate carrier female patients were within the clinical spectrum of a typical X-linked-recessive RP. A novel nonsense RPGR exon ORF15 mutation (912G>T) was found to segregate with RP in this family.

Conclusions

This report expands the clinical heterogeneity spectrum caused by RPGR mutations and our knowledge concerning the molecular pathologic condition that pertains to Coats'-like RP. Consistent with the literature, Coats' response was not observed in all family members who were affected by RP, which suggests the involvement of other genetic and/or environmental factors.

Purpose

A patient with retinitis pigmentosa demonstrated a novel RPGR mutation (213G>A, last base of exon 2) predicted to cause a missense change (G52R) in the final protein. This study was performed to determine whether this mutation altered the effectiveness of the adjacent splice site.

Design

Observational case report.

Methods

Total RNA was extracted from leukocytes of the proband and his carrier mother. Reverse transcription-polymerase chain reaction (RT-PCR) was performed by using the primers flanking exon 2 of RPGR transcript, followed by gel purification and direct sequencing.

Results

Sequencing revealed skipping of exon 2 in the mutated transcript, leading to in-frame deletion of 42 amino acids affecting the critical RCC1-like domain.

Conclusions

The last base of exons is conserved as "G" in 80% of splicing consensus sequences, yet when changed, can completely disrupt constitutive splicing as in this patient. Our data confirm that the evaluation of the effects of some DNA sequence alterations at the RNA level might have important implications for appropriate genotype-phenotype correlations.

Purpose

We evaluated the efficacy of a practice-based survey of age-related maculopathy (ARM) to identify potential families for molecular genetic studies. Demographic and ophthalmic features of the eligible study population were compared with responders and with individuals who reported a positive family history of ARM.

Methods

Individuals seen within a three-year period in a comprehensive ophthalmic practice were identified through billing codes. Clinical records were reviewed, coded, and merged with questionnaire responses. Patient identifiers were removed prior to analyses.

Results

There were no significant differences between the respondents and the eligible cohort with respect to gender, age, or type of macular degeneration. Comparable percentages of younger and older individuals with ARM reported positive family histories. The distribution of atrophic macular degeneration, choroidal neovascular membranes, and milder forms of the disease among the individuals reporting positive family histories corresponded to the distribution of the entire eligible cohort of patients.

Conclusions

This recruitment strategy for ARM families is cost-effective and confirmed a high prevalence of familial ARM. The respondents are representative of the general ARM population. This approach is applicable for other ophthalmic genetic conditions.

On the basis of genomewide linkage studies of families affected with age-related maculopathy (ARM), we previously identified a significant linkage peak on 10q26, which has been independently replicated by several groups. We performed a focused SNP genotyping study of our families and an additional control cohort. We identified a strong association signal overlying three genes, PLEKHA1, LOC387715, and PRSS11. All nonsynonymous SNPs in this critical region were genotyped, yielding a highly significant association (P < .00001) between PLEKHA1/LOC387715 and ARM. Although it is difficult to determine statistically which of these two genes is most important, SNPs in PLEKHA1 are more likely to account for the linkage signal in this region than are SNPs in LOC387715; thus, this gene and its alleles are implicated as an important risk factor for ARM. We also found weaker evidence supporting the possible involvement of the GRK5/RGS10 locus in ARM. These associations appear to be independent of the association of ARM with the Y402H allele of complement factor H, which has previously been reported as a major susceptibility factor for ARM. The combination of our analyses strongly implicates PLEKHA1/LOC387715 as primarily responsible for the evidence of linkage of ARM to the 10q26 locus and as a major contributor to ARM susceptibility. The association of either a single or a double copy of the high-risk allele within the PLEKHA1/LOC387715 locus accounts for an odds ratio of 5.0 (95% confidence interval 3.2-7.9) for ARM and a population attributable risk as high as 57%.

X-linked cone-rod dystrophy (COD1) is a retinal disease that primarily affects the cone photoreceptors; the disease was originally mapped to a limited region of Xp11.4. We evaluated the three families from our original study with new markers and clinically reassessed all key recombinants; we determined that the critical intervals in families 2 and 3 overlapped the RP3 locus and that a status change (from affected to probably unaffected) of a key recombinant individual in family 1 also reassigned the disease locus to include RP3 as well. Mutation analysis of the entire RPGR coding region identified two different 2-nucleotide (nt) deletions in ORF15, in family 2 (delAG) and in families 1 and 3 (delGG), both of which result in a frameshift leading to altered amino acid structure and early termination. In addition, an independent individual with X-linked cone-rod dystrophy demonstrated a 1-nt insertion (insA) in ORF15. The presence of three distinct mutations associated with the same disease phenotype provides strong evidence that mutations in RPGR exon ORF15 are responsible for COD1. Genetic heterogeneity was observed in three other families, including the identification of an in-frame 12-nt deletion polymorphism in ORF15 that did not segregate with the disease in one of these families.

Purpose

To evaluate the donor retina of a patient with X-linked cone-rod dystrophy caused by an RPGR exon ORF15 mutation.

Design

Histopathologic study of the retina.

Methods

The eye of a 69-year-old man was fixed at 1.6 hours postmortem and processed for histopathology and immunocytochemistry.

Results

Grossly, the macula was atrophic with a bull's-eye appearance. The remaining retina showed postmortem edema but no intraretinal pigment. Microscopically, the macular retinal pigment epithelium was absent focally and had pigmentary changes elsewhere. Cones and rods were absent from the perifovea and reduced with shortened outer segments elsewhere in the macula. In the remainder of the retina, cones but not rods were reduced and all photoreceptor outer segments were shortened.

Conclusions

The abnormalities in both cone and rod photoreceptors confirm the importance of RPGR in both cell types but leaves unresolved how various exon ORF15 mutations lead to different clinical phenotypes.

A genetic contribution to the development of age-related macular degeneration (AMD) is well established. Several genome-wide linkage studies have identified a number of putative susceptibility loci for AMD but only a few of these regions have been replicated in independent studies. Here, we perform a meta-analysis of six AMD genome screens using the genome-scan meta-analysis method, which allows linkage results from several studies to be combined, providing greater power to identify regions that show only weak evidence for linkage in individual studies. Results from non-parametric analysis for a broad AMD clinical phenotype (including two studies with quantitative traits) were extracted. For each study, 120 genomic bins of approximately 30 cM were defined and ranked according to maximum evidence for linkage within each bin. Bin ranks were weighted according to study size and summed across all studies; the summed rank (SR) for each bin was assessed empirically for significance using permutation methods. A high SR indicates a region with consistent evidence for linkage across studies. The strongest evidence for an AMD susceptibility locus was found on chromosome 10q26 where genome-wide significant linkage was observed (P=0.00025). Several other regions met the empirical significance criteria for bins likely to contain linked loci including adjacent pairs of bins on chromosomes 1q, 2p, 3p and 16. Several of the regions identified here showed only weak evidence for linkage in the individual studies. These results will help prioritize regions for future positional and functional candidate gene studies in AMD.