Toll-like receptor 3 and geographic atrophy in age-related macular degeneration

BACKGROUND

Age-related macular degeneration is the most common cause of irreversible visual impairment in the developed world. Advanced age-related macular degeneration consists of geographic atrophy and choroidal neovascularization. The specific genetic variants that predispose patients to geographic atrophy are largely unknown.

METHODS

We tested for an association between the functional toll-like receptor 3 gene (TLR3) variant rs3775291 (involving the substitution of phenylalanine for leucine at amino acid 412) and age-related macular degeneration in Americans of European descent. We also tested for the effect of TLR3 Leu and Phe variants on the viability of human retinal pigment epithelial cells in vitro and on apoptosis of retinal pigment epithelial cells from wild-type mice and Tlr3-knockout (Tlr3(-/-)) mice.

RESULTS

The Phe variant (encoded by the T allele at rs3775291) was associated with protection against geographic atrophy (P=0.005). This association was replicated in two independent case-control series of geographic atrophy (P=5.43x10(-4) and P=0.002). No association was found between TLR3 variants and choroidal neovascularization. A prototypic TLR3 ligand induced apoptosis in a greater fraction of human retinal pigment epithelial cells with the Leu-Leu genotype than those with the Leu-Phe genotype and in a greater fraction of wild-type mice than Tlr3(-/-) mice.

CONCLUSIONS

The TLR3 412Phe variant confers protection against geographic atrophy, probably by suppressing the death of retinal pigment epithelial cells. Since double-stranded RNA (dsRNA) can activate TLR3-mediated apoptosis, our results suggest a role of viral dsRNA in the development of geographic atrophy and point to the potential toxic effects of short-interfering-RNA therapies in the eye.

Genetic association of LOXL1 gene variants and exfoliation glaucoma in a Utah cohort

Exfoliation glaucoma (XFG) is the commonest identifiable cause of secondary open-angle glaucoma worldwide, characterized by the deposition of fibrillar proteins in the anterior segment of the eye. We investigated LOXL1 gene variants previously identified to confer susceptibility to XFG in a Utah Caucasian cohort. After a standard eye examination protocol we genotyped SNPs rs2165241and rs3825942 in 62 XFG or exfoliation syndrome (XFS) patients and 170 normal controls. Genotype frequency distribution, odds ratios (ORs) and population attributable risks were calculated for the risk alleles. The SNP rs2165241 was significantly associated with XFG and XFS (p = 4.13 x 10(-9)) for an additive model, OR(het) = 4.42 (2.30-8.50), OR(hom) = 34.19 (4.48-261.00); T allele: 83.1% in cases versus 52.4% in controls). Significant association was also found for rs3825942: (p = 1.89 x 10(-6)). Our findings confirm genetic association of LOXL1 with XFG and XFS and implicate a potential role of cross linking of elastin in the pathogenesis of XFG. This information will potentially guide glaucoma monitoring efforts by targeting individuals whose genetic profiles put them at higher risk for XFG.

Association of HTRA1 polymorphism and bilaterality in advanced age-related macular degeneration

Single nucleotide polymorphism (SNP), rs11200638, in the promoter of HTRA1 has recently been shown to increase the risk for AMD. In order to investigate the association of this HTRA1 polymorphism and the bilaterality of AMD, we genotyped rs11200638 in control, unilateral, and bilateral advanced AMD patients. The A allele for SNP rs11200638 in HTRA1, was significantly more prevalent in bilateral wet AMD and GA patients than in unilateral groups (p=.02 and p=.03, respectively). The homozygote odds ratios of bilateral wet AMD and GA are significantly greater than those seen in unilateral groups (twofold and threefold increase, respectively). This finding is consistent with the role of HTRA1 in AMD pathogenesis and will help aid in the clinical management and prognosis of AMD patients.

Clinical characterization and genetic mapping of North Carolina macular dystrophy

North Carolina macular dystrophy (NCMD) is an autosomal dominant macular disease, was mapped to 6q14-q16.2, the disease-causing gene has yet not been identified. It shares phenotypic similarity with age-related macular degeneration including drusen and choroidal neovascularization. We collected six families with NCMD including 75 members, and conducted clinical characterization and genetic mapping for these families. Forty-five patients were diagnosed as NCMD; all six NCMD families were mapped to MCDR1 locus using genetic linkage analysis. MCDR1 interval was refined to 3 cM (1.8mb) between D6S1716 to D6S1671 via fine mapping using microsatellite markers in these six families, all eleven annotated genes within the interval were analyzed by mutation screening in coding regions, no mutation was found, suggesting a potential novel gene or a new pathological mechanism causing NCMD. The refinement of MCDR1 locus will aid the disease-causing gene identification. Functional studies of NCMD genes should provide important insights into pathogenetic mechanisms of NCMD and age-related macular degeneration.

The R345W mutation in EFEMP1 is pathogenic and causes AMD-like deposits in mice

Age-related macular degeneration (AMD) is the most common cause of vision loss in developed countries. A defining characteristic of this disorder is the accumulation of material between Bruch's membrane and the retinal pigment epithelium (RPE), first as microscopic basal deposits and later as clinically evident drusen. The pathogenesis of these deposits remains to be defined. Biochemical and genetic studies have suggested that inflammation and complement activation may play roles in AMD. Several lines of evidence also suggest that alterations to the extracellular matrix (ECM) of the RPE and choroid contribute to the development of AMD. The inherited macular degeneration Doyne honeycomb retinal dystrophy/Malattia Leventinese is thought to be caused by an R345W mutation in the EFEMP1 gene (also called fibulin-3). The pathogenicity of this mutation has been questioned because all individuals identified to date with the R345W mutation have shared a common haplotype. We investigated the pathogenicity of this mutation in families with early-onset macular degeneration and by generating Efemp1-R345W knockin mice. Genetic studies show that one of the identified families with the R345W mutation has a novel haplotype. The mutant Efemp1-R345W mice develop deposits of material between Bruch's membrane and the RPE, which resemble basal deposits in patients with AMD. These basal deposits contain Efemp1 and Timp3, an Efemp1 interacting protein. Evidence of complement activation was detected in the RPE and Bruch's membrane of the mutant mice. These results confirm that the R345W mutation in EFEMP1 is pathogenic. Further, they suggest that alterations in the ECM may stimulate complement activation, demonstrating a potential connection between these two etiologic factors in macular degeneration.

Elovl4 haploinsufficiency does not induce early onset retinal degeneration in mice

ELOVL4 was first identified as a disease-causing gene in Stargardt macular dystrophy (STGD3, MIM 600110.) To date, three ELOVL4 mutations have been identified, all of which result in truncated proteins which induce autosomal dominant juvenile macular degenerations. Based on sequence homology, ELOVL4 is thought to be another member within a family of proteins functioning in the elongation of long chain fatty acids. However, the normal function of ELOVL4 is unclear. We generated Elovl4 knockout mice to determine if Elovl4 loss affects retinal development or function. Here we show that Elovl4 knockout mice, while perinatal lethal, exhibit normal retinal development prior to death at day of birth. Further, postnatal retinal development in Elovl4 heterozygous mice appears normal. Therefore haploinsufficiency for wildtype ELOVL4 in autosomal dominant macular degeneration likely does not contribute to juvenile macular degeneration in STGD3 patients. We found, however, that Elovl4+/- mice exhibit enhanced ERG scotopic and photopic a and b waves relative to wildtype Elovl4+/+ mice suggesting that reduced Elovl4 levels may impact retinal electrophysiological responses.

A variant of the HTRA1 gene increases susceptibility to age-related macular degeneration

Age-related macular degeneration (AMD) is the most common cause of irreversible vision loss in the developed world and has a strong genetic predisposition. A locus at human chromosome 10q26 affects the risk of AMD, but the precise gene(s) have not been identified. We genotyped 581 AMD cases and 309 normal controls in a Caucasian cohort in Utah. We demonstrate that a single-nucleotide polymorphism, rs11200638, in the promoter region of HTRA1 is the most likely causal variant for AMD at 10q26 and is estimated to confer a population attributable risk of 49.3%. The HTRA1 gene encodes a secreted serine protease. Preliminary analysis of lymphocytes and retinal pigment epithelium from four AMD patients revealed that the risk allele was associated with elevated expression levels of HTRA1 mRNA and protein. We also found that drusen in the eyes of AMD patients were strongly immunolabeled with HTRA1 antibody. Together, these findings support a key role for HTRA1 in AMD susceptibility and identify a potential new pathway for AMD pathogenesis.

Reduced beta cell function in offspring of mothers with young-onset type 2 diabetes

AIMS/HYPOTHESIS

Animal models indicate that even exposure to mild maternal hyperglycaemia in utero is detrimental to the beta cell function of the offspring, but evidence of this in humans is limited. In Europids who are diagnosed with type 2 diabetes before the age of 50 years, the risk of diabetes in the offspring of the diabetic mothers is greatly increased compared with the risk in those born to diabetic fathers. We hypothesised that offspring born to mothers with young-onset type 2 diabetes would have been exposed to mild hyperglycaemia in utero, so we studied the impact of this on their beta cell function.

SUBJECTS AND METHODS

We measured beta cell function using early insulin response (EIR) after oral glucose; insulin resistance using HOMA; and HbA(1c) in 568 non-diabetic adult offspring born to parents with type 2 diabetes (mean age 55.8 years), split according to which parent was affected (in 327 it was the mother) and parental age of diagnosis: <50 years (n=117) or > or =50 years. To reduce the impact of genetic susceptibility, the offspring of affected fathers were used as control subjects.

RESULTS

Offspring of mothers with young-onset type 2 diabetes had lower EIR (log EIR 4.32, 95% CI [4.14-4.51] vs 4.63 [4.43-4.83] p=0.02) and higher HbA(1c) (4.89% [4.79-4.99] vs 4.68% [4.57-4.79] p=0.02) than the offspring of fathers with young-onset type 2 diabetes. Insulin sensitivity was similar in the two groups. There were no differences in EIR or HbA(1c) between the offspring born to mothers and fathers who were diagnosed after the age of 50 years.

CONCLUSIONS/INTERPRETATION

We conclude that the offspring of mothers with young-onset type 2 diabetes have a reduction in beta cell function. This is consistent with exposure to mild maternal hyperglycaemia programming beta cell function.

A novel locus for X-linked retinitis pigmentosa

INTRODUCTION

Retinitis pigmentosa (RP) is the most prevalent group of inherited retinopathies and demonstrates considerable clinical and genetic heterogeneity, with wide variations in disease severity, progression, and gene involvement. We studied a large family with RP to determine the pattern of inheritance and to identify the disease-causing gene/locus.

MATERIALS AND METHODS

Ophthalmic examination was performed on 35 family members to identify affected individuals and carriers and to characterise the disease phenotype. Genetic linkage analysis was performed using short tandem repeat (STR) polymorphic markers encompassing the known loci for Xlinked RP (xlRP) including RP2, RP3, RP6, RP23, and RP24. Mutation screening was performed by direct sequencing of PCR-amplified genomic DNA of the RP2 and RPGR genes of the affected individuals.

RESULTS

A highly penetrant, X-linked form of RP was observed in this family. Age of onset was from 5 to 8 years and visual acuity ranged from 20/25 in children to light perception in older adults. Linkage analysis and direct sequencing showed that no known loci/genes were associated with the phenotype in this kindred.

CONCLUSION

A novel disease gene locus/loci is responsible for the xlRP phenotype in this family.

Development of a nurse-led skin camouflage clinic

This article outlines the development of an outpatient skin camouflage service and summarises findings from an audit of the service after one year, which resulted in the clinic expanding to a monthly all-day session.

Loss of ER retention and sequestration of the wild-type ELOVL4 by Stargardt disease dominant negative mutants

PURPOSE

Mutations in ELOVL4, a member of the fatty acid elongase (ELO) family, are responsible for autosomal dominant Stargardt-like macular degeneration. The specific role of ELOVL4 in photoreceptors and the degenerative events induced by dominant ELOVL4 mutations are not well understood. As a first step to identifying possible mechanisms contributing to cellular dysfunction, we transfected HEK293 and COS cells with fluorescent-labeled wild-type and mutant ELOVL4 constructs. Effects of mutant ELOVL4 on interaction with wild-type protein were examined in this in vitro model.

METHODS

Wild-type and mutant ELOVL4 proteins including ELOVL4 truncation (270X, a truncated ELOVL4 protein at amino acid position 270) and ELOVL4 5 bp deletion (5bp-del) and ELOVL4 (5A, substituting the ER retention signal, KAKGD, with a five alanine amino acid tract) were expressed as EGFP or DsRed fusion proteins. Cellular localization of these proteins was examined by fluorescence microscopy. ELOVL4 protein aggregates were measured by co-immunoprecipitation and by sucrose gradient centrifugation followed by immunodetection with western blots. To study cellular status of cells expressing mutant ELOVL4 proteins, transfected cells were examined for upregulation of Bip and CHOP, markers for the unfolded protein response (UPR) by western blotting.

RESULTS

ELOVL4 mutants were not retained within the ER but were rather mislocalized and formed aggregates. Importantly, when cotransfected with wild-type ELOVL4, the mutants bound to and sequestered the wild-type protein into the aggregates. Expression of ELOVL4 mutants also induced UPR as evidenced by Bip and CHOP expression.

CONCLUSIONS

Using this in vitro cell system, we have identified alterations in wild-type ELOVL4 protein localization, aggregate formation, and the induction of cellular stress by the ELOVL4 mutants. We propose that "inactivation" of the wild-type ELOVL4 protein through sequestration to a non-ER compartment by ELOVL4 mutants may play a role in cellular dysfunction.

Early and late morbidity after vasectomy: a comparison of chronic scrotal pain at 1 and 10 years

OBJECTIVE

To evaluate the incidence and timing of the onset of chronic scrotal pain after vasectomy in two populations at 1 and 10 years after surgery.

PATIENTS AND METHODS

In a retrospective questionnaire-based study two groups of men were compared; 460 who had a vasectomy in 1991-92 (group A) and another 460 who had a vasectomy in 2000-1 (group B; 10 and 1 year after surgery, respectively). Data were collected on immediate complications, and the incidence and nature of chronic scrotal pain. Pain severity was graded using a visual analogue score (VAS). Patients were also asked if they regretted having a vasectomy because of pain.

RESULTS

In all, 182 and 220 replies were received from patients in group A and B, respectively. Early complications included haematoma in five (2%) and two (0.9%) patients, respectively, and wound infection in 24 (13%) and 17 (7.7%). Eight patients who had scrotal pain even before vasectomy were excluded from the analysis (two in group A and six in group B). In group A, 25 of 180 (13.8%) had a new onset of scrotal pain of some nature, with eight (4.3%) having a VAS of > 5; one patient had an epididymectomy for this. Three of the 25 regretted having a vasectomy because of pain. In group B, 36 of 214 (16.8%) reported persistent scrotal pain, with 13 (5.9%) having a VAS of > 5. Six of the 36 regretted having a vasectomy because of the pain. The incidence of scrotal pain was not significantly different between the groups (P = 0.48, Fisher's exact test).

CONCLUSION

Chronic scrotal pain after vasectomy is more common than previously described, affecting almost one in seven patients. All patients undergoing vasectomy must receive appropriate preoperative counselling about this. The incidence of this complication does not appear to increase with time.

Partner's influence on patient preference for treatment in early prostate cancer

OBJECTIVE

To determine the partner's influence on the patient's choice of treatment for early prostate cancer, and whether partner characteristics and biases predict the preference.

PATIENTS, SUBJECTS AND METHODS

Questionnaires for partners to complete retrospectively were sent to consecutive patients recruited in a study comparing treatment options for early prostate cancer. The partners' perceptions about prostate cancer were explored and the partners asked to comment on the suitability of each treatment option. Partners recorded their influence on the patient's choice using a 10-point visual linear analogue scale.

RESULTS

Questionnaires were sent to 116 eligible patients and 82 were returned for analysis (mean partner age 63 years). When asked to recall the treatment options initially discussed, all partners recalled radiotherapy (EBRT), all but one radical prostatectomy (RP), 51% brachytherapy, but only 29% watchful waiting (WW); 41% of partners stated RP as their chosen option, 37% EBRT, 12% brachytherapy and 10% no clear favourite. None preferred WW. Employment and education status were not significant predictors of partners' preference but retired partners and those aged > 65 years were 3 times more likely to prefer EBRT than were their employed and younger counterparts, respectively. The partners' mean (median, SD) self-assessed influence factor was 4.8 (5, 3.4). Of the partners, 88% reported active involvement throughout the process, identifying information-gathering and emotional support as their primary roles. Most deliberately chose not to influence the patient's final decision.

CONCLUSION

Partner preference is influenced by pre-existing conceptions about cancer and its treatment. While undoubtedly influential throughout the decision-making process, partners deliberately left the final decision to the patient.

beta-cell genes and diabetes: molecular and clinical characterization of mutations in transcription factors

beta-Cell transcription factor genes are important in the pathophysiology of the beta-cell, with mutations in hepatocyte nuclear factor (HNF)-1alpha, HNF-4alpha, insulin promoter factor (IPF)-1, HNF-1beta, and NeuroD1/BETA2, all resulting in early-onset type 2 diabetes. We assessed the relative contribution of these genes to early-onset type 2 diabetes using linkage and sequencing analysis in a cohort of 101 families (95% U.K. Caucasian). The relative distribution of the 90 families fitting maturity-onset diabetes of the young (MODY) criteria was 63% HNF-1alpha, 2% HNF-4alpha, 0% IPF-1, 1% HNF-1beta, 0% NeuroD1/ BETA2, and 20% glucokinase. We report the molecular genetic and clinical characteristics of these patients including 29 new families and 8 novel HNF-1alpha gene mutations. Mutations in the transactivation domain are more likely to be protein truncating rather than result in amino acid substitutions, suggesting that a relatively severe disruption of this domain is necessary to result in diabetes. Mutations in the different transcription factors result in clinical heterogeneity. IPF-1 mutations are associated with a higher age at diagnosis (42.7 years) than HNF-1alpha (20.4 years), HNF-1beta (24.2 years), or HNF-4alpha (26.3 years) gene mutations. Subjects with HNF-1beta mutations, in contrast to the other transcription factors, frequently present with renal disease. A comparison of age at diagnosis between subjects with different types and locations of HNF-1alpha mutations did not reveal genotype-phenotype correlations. In conclusion, mutations in transcription factors expressed in the beta-cell are the major cause of MODY, and the phenotype clearly varies with the gene that is mutated. There is little evidence to indicate that different mutations within the same gene have different phenotypes.