Recurrence risks for Bardet-Biedl syndrome: Implications of locus heterogeneity

PURPOSE

Bardet-Biedl syndrome is a pleiotropic multiple anomaly syndrome inherited in an autosomal recessive pattern. It is now known that this disorder has locus heterogeneity, with causative mutations identified in as many as 14 genes. The aim of this study was to derive locus-specific recurrence risk estimates for family members of a proband affected with Bardet-Biedl syndrome.

METHODS

Mutation data from 187 probands affected with Bardet-Biedl syndrome were used. The authors counted the relative proportion of families with mutations at each of 10 loci and estimated locus-specific carrier rates for mutations using Hardy-Weinberg principles and an aggregate population frequency of 1/100,000 for the phenotype. Locus-specific recurrence risks were calculated for relatives of an affected proband.

RESULTS

Locus-specific carrier frequencies range from 1/250 to 1/2200, and the risks for an offspring of the sibling of an affected individual range from 1/1,500 to 1/13,000. The estimate of this risk derived under a locus homogeneity model is 1/960.

CONCLUSION

Variation of recurrence risks of this magnitude may have implications for genetic counseling of families with affected individuals, in particular about prenatal testing and other reproductive options. Similar analyses to determine locus-specific carrier frequencies for other phenotypes with significant locus heterogeneity may yield similarly relevant results.

Clinical phenotype of posterior polymorphous corneal dystrophy in a family with a novel ZEB1 mutation

PURPOSE

To describe the clinical phenotype in a family with posterior polymorphous corneal dystrophy (PPCD) and a novel mutation in the ZEB1 gene.

METHODS

 Clinical examination, anterior segment photography, specular microscopy and electrophysiological investigations were performed and quantified. Genomic DNA extracted from peripheral blood was sequenced for ZEB1 exons. Cosegregation of identified mutation with the disease status in the family was confirmed using polymerase chain reaction and restriction fragment length polymorphism.

RESULTS

Ocular examination was performed on five family members from two generations. Three had anomalies of the corneal endothelium that were consistent with PPCD. Endothelial cell counts ranged from 2306 to 2987 mm(2) (ref. 2000-4000 cells/mm(2) ). No evidence of glaucoma or retinal abnormalities was observed. Extraocular abnormalities such as inguinal herniation, hydrocoele and possible bony or connective tissue anomalies were part of the disease spectrum in this family. Mutation analysis revealed a novel change in exon 5 of ZEB1 (c.672delA) that cosegregated with the affected disease status.

CONCLUSION

The detailed clinical features of PPCD associated with a novel ZEB1 mutation are supportive of the previously proposed range of phenotype parameters. Further phenotype-genotype correlations may provide insights into the clinical variability and pathological processes affecting the corneal endothelium, Descemet's membrane, retinal photoreceptor function and extraocular tissues of some patients.

Using RB1 mutations to assess minimal residual disease in metastatic retinoblastoma

To assess complete remission before subjecting nongermline metastatic retinoblastoma patients to an autologous peripheral stem cell transplant, we tested for patient-specific retinoblastoma tumor suppressor gene (RB1) mutant alleles in cerebrospinal fluid (CSF) and bone marrow. In 1 child with CSF and 1 with bone marrow metastases, allele-specific polymerase chain reaction (AS-PCR) detected the biallelic RB1 mutations specific to their tumors. The tumor of Child A was homozygous for R251X, and in Child B, it was homozygous for R358X. In Child A, the R251X mutation was detected in mutant controls diluted to 1:12,800 but not in CSF samples, corroborating clinical remission after chemotherapy. In Child B's bone marrow, AS-PCR for R358X was strongly positive at the detection of relapse, and subsequent bone marrow samples corroborated clinical remission after chemotherapy. No mutant tumor RB1 alleles were detected in their harvested peripheral blood stem cells. Both children were deemed suitable candidates for supralethal-dosage consolidation chemotherapy followed by autologous peripheral stem cell rescue of the bone marrow aimed at curing their metastatic retinoblastoma. When Child A recurred, the mutant tumor RB1 allele was detected 3.5 months before conventional pathology detected retinoblastoma tumor cells in the CSF. Assaying tumor-specific RB1 mutations complements cytological and immunohistochemical assessment of retinoblastoma involvement of CSF and bone marrow. Tumor cells can be detected in numbers lower than possible by conventional methods. An early diagnosis of relapse may allow an early institution of new therapy. A prospective international multicenter trial of the rare patients with metastatic retinoblastoma would assess the role of molecular monitoring in surveillance for minimal residual disease and recurrence.

Mutations in chaperonin-like BBS genes are a major contributor to disease development in a multiethnic Bardet-Biedl syndrome patient population

BACKGROUND

Bardet-Biedl syndrome is a pleiotropic disorder with 14 BBS genes identified. BBS1, BBS2, BBS4, BBS5, BBS7, BBS8, and BBS9 form a complex called the BBSome, which is believed to recruit Rab8(GTP) to the primary cilium and promote ciliogenesis. The second group, the chaperonin-like proteins BBS6, BBS10, and BBS12, have been defined as a vertebrate-specific branch of the type II chaperonin superfamily. These may play a role in the regulation of BBSome assembly.

METHODS AND RESULTS

Using sequence analysis, the role of BBS6, 10 and 12 was assessed in the patient population comprising 93 cases from 74 families. Systemic and ocular phenotypes were defined. In the study, chaperonin-like BBS gene mutations accounted for the disease in approximately 36.5% of BBS families. A total of 38 different non-polymorphic exonic sequence variants were identified in 40.5% of BBS families (41.9% cases), of which 26 were novel (68%). Six cases had mutations present in more than one chaperonin-like BBS gene. One case with four mutations in BBS10 had a phenotype of overall greater severity. The phenotypes observed were beyond the classic BBS phenotype as they overlapped with characteristics of MKKS (congenital heart defect, vaginal atresia, hydrometrocolpos, cryptorchidism), as well as Alström syndrome (diabetes, hearing loss, liver abnormalities, endocrine anomalies, cardiomyopathy).

CONCLUSIONS

While overlap between the MKKS and BBS phenotypes has previously been reported for cases with BBS6 mutations, we also observed MKKS phenotypes involving BBS10 and BBS12 and Alström-like phenotypes associated with mutations in BBS1, BBS2, BBS6, BBS7, BBS9, BBS10 and BBS12 for the first time.

Retinoblastoma CSF metastasis cured by multimodality chemotherapy without radiation

OBJECTIVE

Cerebrospinal fluid (CSF) metastasis is the most difficult type of retinoblastoma metastasis to cure, even with bone marrow transplant. Most metastatic retinoblastoma cells express P-glycoprotein causing multidrug resistance (MDR). P-glycoprotein-rich blood vessels form blood-brain and blood-eye barriers, inhibit drug entry into central nervous system (CNS) and eyes. High-dose craniospinal radiation is too morbid for treatment of young children. To cure CSF metastasis without radiation, we designed an intensive multimodality chemotherapy regimen.

METHOD

After left eye enucleation, a 4-month-old boy with bilateral International Intraocular Retinoblastoma Classification Group E eyes and CSF metastasis was treated with 7-cycle high-dose carboplatin and etoposide, standard-dose vincristine, and high-dose/short-infusion cyclosporine to inhibit P-glycoprotein. Intraventricular drugs, non-substrate of P-glycoprotein (cytarabine), or less susceptible to MDR (topotecan), contributed to treatment of the metastasis. On achieving complete response, he was consolidated with supralethal-dosage carboplatin, etoposide, and cyclophosphamide, and his bone marrow rescued with autologous cord blood stem cells.

RESULTS

Following 1-cycle systemic chemotherapy and 2-dose intraventricular chemotherapy, the CSF metastasis cleared. The right eye tumor regressed completely. The patient remains in remission 8.3 years after diagnosis and 7.8 years post-transplant.

CONCLUSION

Intensive multimodality chemotherapy can cure CSF metastasis in retinoblastoma without incurring extreme morbidity from craniospinal radiation.

Management and outcome of unilateral retinoblastoma

BACKGROUND

Two-thirds of retinoblastoma cases are unilateral, with most presenting with an advanced stage of disease. Primary enucleation is usually the preferred treatment. Conservative therapy may save less involved eyes.

METHODS

We retrospectively reviewed the presentation, age at diagnosis, classification, genetic status, treatment, and long-term outcome of 130 patients with unilateral retinoblastoma (1988-2008).

RESULTS

The mean age at presentation was 26 months. Based on retinoblastoma gene (RB1) status in tumors, germ-line status was defined in 92% of patients; 13% had a germ-line mutation. The primary treatment of 106 patients was enucleation. Severe disease at presentation (International Intraocular Retinoblastoma Classification [IIRC] group E) was significantly (p < 0.001) associated with adverse histopathological risk factors. Of the 16 patients who underwent eye-conserving therapy, treatment was successful in 9 (IIRC group A, 1; B, 5; C, 3). Two patients with a pertinent family history were diagnosed early and were treated solely with focal therapy. Three patients retained vision of 6/18 or better in the treated eye (median follow-up, 33 months; range, 2-120 months). Seven patients (IIRC group: B, 2; C, 4; D, 1) eventually underwent enucleation. One patient died of metastases following delayed parental consent for enucleation and refusal of prophylactic chemotherapy for high-risk histopathologic features.

CONCLUSIONS

Chemotherapy/focal therapy can save selected eyes, but primary enucleation is preferred for advanced unilateral retinoblastoma. "Conservative" treatment is an option when there is good potential for useful vision without prolonged, costly therapy with potential side effects. Simple enucleation reduces the risk of masking high-risk pathology and promotes early return to normal life.

Ocular manifestations of the Johanson-Blizzard syndrome

Johanson-Blizzard syndrome is a rare autosomal-recessive congenital disorder characterized by hypoplastic nasal alae, midline scalp defects, deafness, microcephaly, hypothyroidism, absent permanent teeth, malabsorption, and failure to thrive. The literature was reviewed to define the reported spectrum of ocular manifestations, which are not well documented. We found that nasolacrimal system malformations are a common feature of Johanson-Blizzard, whereas intraocular malformations are rare. This report describes the ophthalmologic findings and management of 2 affected children.

BBS7 and TTC8 (BBS8) mutations play a minor role in the mutational load of Bardet-Biedl syndrome in a multiethnic population

Bardet Biedl syndrome is a genetically heterogeneous ciliopathy with fourteen genes currently identified. To date, mutations in BBS7 and TTC8 (BBS8) were reported in 4.2% and 2.8% of BBS families respectively. We sequenced the coding regions of BBS7 and TTC8 in 35 BBS families of diverse ancestral backgrounds. In addition, the role of putative modifier genes on phenotype severity; NXNL1 and MGC1203 c.430C>T, was assessed. Genotype-phenotype correlation was explored in patients with identified mutations. Four novel pathogenic BBS7 changes were identified in 2/35 families (5.7%). In one family with two affected individuals with BBS7 mutations, a more severe phenotype was observed in association with a third mutation in BBS4. The overall retinal phenotype appeared more severe than that seen in patients with BBS1 mutations. This study confirms the small role of BBS7 and TTC8 in the overall mutational load of BBS patients. The variability of the ocular phenotype observed, could not be explained by the putative modifier genes; NXNL1 and MGC1203 c.430C>T.

Detailed analysis of retinal function and morphology in a patient with autosomal recessive bestrophinopathy (ARB)

The objective of the paper is to study the retinal microstructure and function in a patient with autosomal recessive bestrophinopathy (ARB). Retinal function and morphology assessment in a patient diagnosed with a biallelic mutation in the BEST1 gene (heterozygote mutations: Leu88del17 and A195V) included: full-field electroretinogram (ffERG) and multifocal electroretinogram (mfERG), electro-oculogram (EOG) testing, and imaging with a high-resolution Fourier-domain optical coherence tomography (Fd-OCT) system (UC Davis Medical Center; axial resolution: 4.5 microm, acquisition speed: 9 frames/s, 1,000 A-scans/frame) combined with a flexible scanning head (Bioptigen Inc.). The 11-year old asymptomatic boy showed a well-demarcated retinopathy with deposits. Functional assessment revealed normal visual acuity, reduced central mfERG responses, delayed rod and rod-cone b-wave ffERG responses, and reduced light rise in the EOG. Fd-OCT demonstrated RPE deposits, photoreceptor detachment, elongated and thickened photoreceptor outer segments, but preserved inner retinal layers. In conclusion, ARB associated retinal dystrophy shows functional and morphological changes that overlap with classic Best disease. For the first time, high-resolution imaging provided in vivo evidence of RPE and photoreceptor involvement in ARB.

The need for standardization of antiretinal antibody detection and measurement

PURPOSE

To review the current literature on the detection and measurement of antiretinal antibodies.

DESIGN

Collaborative essay.

METHODS

Literature review and interpretation.

RESULTS

There is strong evidence to suggest a role for antiretinal antibodies, particularly those targeting recoverin and alpha-enolase, in the pathogenesis of autoimmune retinopathy (AIR). Additionally, numerous other autoantibodies have been described as putative mediators of retinal degeneration and more remain to be discovered. However, assay methods described in the literature by many laboratories for the detection of circulating antiretinal antibodies have been varied and diverse, making it difficult to interpret and compare their results.

CONCLUSIONS

There is currently little standardization of laboratory methods used to detect and monitor antiretinal antibodies. To measure and monitor levels of circulating antiretinal antibodies optimally in patients with AIR, development of standardized assays with stringent internal controls is required. A multicenter collaborative and validation effort is encouraged to reach a consensus on this issue.

Trilateral retinoblastoma with pituitary-hypothalamic dysfunction

Trilateral retinoblastoma is characterized by retinal tumors in one or both eyes, as well as tumors of the pineal gland or parasellar region of the brain. Here we describe a 4-month-old girl, presenting with pituitary dysfunction, hypothalamic overgrowth syndrome and central blindness, in addition to suprasellar and bilateral retinal tumors. Biopsy of the suprasellar tumor confirmed the diagnosis of trilateral retinoblastoma. After biopsy, cerebrospinal fluid (CSF) metastasis was discovered. Overgrowth persisted, but blindness and pituitary dysfunction resolved when the suprasellar tumor and CSF metastasis responded to cyclosporine-modulated systemic chemotherapy with intraventricular chemotherapy, consolidated with marrow-ablative chemotherapy and stem cell rescue of the bone marrow. Twenty months after diagnosis and 12 months after transplant, an unusual pattern of tumor recurrence was observed along the catheter of the Ommaya reservoir used for delivering intraventricular chemotherapy, which was also at the site of the previous suprasellar needle biopsy. Salvage therapy consisted of resection, stereotactic radiation, and further systemic and intraventricular chemotherapy. At 25 months after diagnosis, the patient was developing well and seeing better. However, she died 32 months after diagnosis despite the salvage therapy. This case highlights the possibility of tumor dissemination after needle biopsy of a suprasellar tumor. Biopsy may be avoided if a characteristic clinicoradiological picture of trilateral retinoblastoma is recognized. We recommend that if a pineal or suprasellar tumor is observed in a child, the eyes should be examined for retinoblastoma, thereby avoiding biopsies of the intracranial tumor, which may track difficult-to-treat tumor cells through the brain, and disseminate tumor cells into the CSF.

Retinal morphological changes of patients with X-linked retinoschisis evaluated by Fourier-domain optical coherence tomography

OBJECTIVE

To investigate the retinal microstructure and lamination of patients affected with X-linked retinoschisis (XLRS) using high-resolution imaging modalities.

METHODS

Patients diagnosed as having XLRS underwent assessment. Visual function testing included visual acuity, color vision, and full-field electroretinography. We used a high-resolution Fourier-domain optical coherence tomography (FD-OCT) system (4.5-mum axial resolution; 9 frames/s; 1000 A-scans per frame) combined with a handheld scanner. Macular image evaluation included schisis localization and retinal layer integrity.

RESULTS

Six patients with XLRS and identified mutations in the XLRS1 gene underwent testing. Visual acuity ranged from 0.2 to 1.6 logMAR (logarithm of the minimum angle of resolution). Results of FD-OCT revealed foveal schisis extending from the outer to the inner plexiform layer in 4 of 6 patients. Bullous foveal schisis was associated with younger age. All patients showed extrafoveal schisis within the outer and inner nuclear and ganglion cell layer, alone or in combination. Photoreceptor outer and inner segment layers were disrupted and irregular in all patients.

CONCLUSIONS

Retinal dystrophy in XLRS is reflected by morphological changes within the inner and outer retinal layers. Disturbed foveal photoreceptor integrity was identified in all patients. Retinal layer abnormalities correlated with age but did not appear to correlate with visual acuity or genotypic variation.

An essential role for DYF-11/MIP-T3 in assembling functional intraflagellar transport complexes

MIP-T3 is a human protein found previously to associate with microtubules and the kinesin-interacting neuronal protein DISC1 (Disrupted-in-Schizophrenia 1), but whose cellular function(s) remains unknown. Here we demonstrate that the C. elegans MIP-T3 ortholog DYF-11 is an intraflagellar transport (IFT) protein that plays a critical role in assembling functional kinesin motor-IFT particle complexes. We have cloned a loss of function dyf-11 mutant in which several key components of the IFT machinery, including Kinesin-II, as well as IFT subcomplex A and B proteins, fail to enter ciliary axonemes and/or mislocalize, resulting in compromised ciliary structures and sensory functions, and abnormal lipid accumulation. Analyses in different mutant backgrounds further suggest that DYF-11 functions as a novel component of IFT subcomplex B. Consistent with an evolutionarily conserved cilia-associated role, mammalian MIP-T3 localizes to basal bodies and cilia, and zebrafish mipt3 functions synergistically with the Bardet-Biedl syndrome protein Bbs4 to ensure proper gastrulation, a key cilium- and basal body-dependent developmental process. Our findings therefore implicate MIP-T3 in a previously unknown but critical role in cilium biogenesis and further highlight the emerging role of this organelle in vertebrate development.

The transport of protein complexes and associated cargo along microtubule tracks represents an essential eukaryotic process responsible for a multitude of cellular functions, including cell division, vesicle movement to membranes, and trafficking along dendrites, axons, and cilia. The latter organelles are hair-like cellular appendages implicated in cell and fluid motility, sensing and transducing information from their environment, and development. Their biogenesis and maintenance depends on a kinesin- and dynein-mediated motility process termed intraflagellar transport (IFT). In addition to comprising these specialized molecular motors, the IFT machinery consists of large multisubunit complexes whose exact composition and organization has not been fully defined. Here we identify a protein, DYF-11/MIP-T3, that is conserved in all ciliated organisms and is associated with IFT in C. elegans. Disruption of C. elegans DYF-11 results in structurally compromised cilia, likely as a result of IFT motor and subunit misassembly. Animals lacking DYF-11 display chemosensory anomalies, consistent with a role for the protein in cilia-associated sensory processes. In zebrafish, MIP-T3 is essential for gastrulation movements during development, similar to that observed for other ciliary components, including Bardet-Biedl syndrome proteins. In conclusion, we have identified a novel IFT machinery component that is also essential for development in vertebrates.

Genetic analysis of chromosome 20-related posterior polymorphous corneal dystrophy: genetic heterogeneity and exclusion of three candidate genes

PURPOSE

Posterior polymorphous corneal dystrophy (PPCD) is a genetically heterogeneous autosomal dominant condition which maps to the pericentromeric region of chromosome 20. Mutations in the VSX1 transcription factor have been reported in patients affected with PPCD, keratoconus, or a combination of both phenotypes. However, no mutation was identified in the coding region of VSX1 in the family used for the original mapping. To clarify the genetic basis of PPCD1, a thorough analysis was performed on the original PPCD1 family and two other PPCD1-linked families. As part of the analysis, the expression profile, transcript variants, and evolutionary conserved regions of VSX1, a key candidate gene within the linkage interval, were characterized.

METHODS

Haplotype analysis was performed using highly informative markers on the pericentromeric region of chromosome 20. VSX1 transcript variants were identified using RT-PCR and characterized by 3'RACE assay. Temporal expression profile of VSX1 was evaluated using semi-quantitative real-time RT-PCR on human tissues. Evolutionary conserved regions (ECRs) were identified in the vicinity of VSX1 using publicly available sequence alignments (UCSC and rVista) and sequenced for mutation analysis.

RESULTS

Recombination events were identified that narrow the PPCD1-disease interval from 20 to 16.44 cM. This smaller interval includes the CHED1 locus and a recently described PPCD locus in Czech families. The three strongest candidate genes of the PPCD1-CHED1 overlap region (RBBP9, ZNF133, SLC24A3) did not show any mutations in our PPCD1-linked families. Semi-quantitative real-time RT-PCR detected VSX1 expression in neonatal human cornea. Six transcript variants of VSX1 were characterized. Four of the transcript variants spliced to two novel exons downstream of the gene. Mutation analysis of the PPCD1-linked families did not reveal any mutations in the full genomic sequence of VSX1 (considering all splice variants) or in the six cis- regulatory modules predicted in the vicinity of VSX1 (100 kb).

CONCLUSIONS

This is the first documentation of VSX1 expression in human neonatal cornea. We provide evidence for genetic heterogeneity of chromosome 20-related PPCD and refinement of the original PPCD1 interval. The full genomic sequence of VSX1 and coding exons of three other candidate genes were excluded from being pathogenic in the original PPCD1 family.

Retinal morphology in patients with BBS1 and BBS10 related Bardet-Biedl Syndrome evaluated by Fourier-domain optical coherence tomography

Retinal dystrophy in Bardet-Biedl Syndrome (BBS) is caused by defective genes that are expressed within ciliated cells such as photoreceptors. The purpose of this study was to characterize and compare the retinal structure and lamination of two groups of patients, carrying mutations in BBS1 or BBS10. Eight patients with BBS (ages 11.9-28.5 years) and mutations in BBS1 (4/8) or BBS10 (4/8) were tested. A high-resolution hand-held probe Fourier-domain optical coherence tomography system (Fd-OCT) was used for retinal image acquisition. Macular scans were evaluated with respect to structure, retinal layering and photoreceptor integrity. Micro-structural in-vivo analysis showed abnormalities within retinal layers but preserved retinal lamination. Photoreceptor integrity was disrupted in all patients. Macular scans from patients with BBS10 mutations most often showed 'deposits' adjacent and anterior to Bruch's membrane. Age, genotype and presence of macular changes did not correlate with the structural changes observed. Retinal dystrophy in BBS is reflected by major changes in the outer retinal layers. This is the first report of in-vivo micro-structural analysis of retinal layers in patients with BBS. Mutations in different BBS genes seem to be associated with similar micro-structural changes in retinal layers.

The Ocular Genetics Program: multidisciplinary care of patients with ocular genetic eye disease

BACKGROUND

Patients who suffer from ocular genetic diseases have special needs in terms of diagnosis and management of rare entities, low-vision needs, genetic counselling, and psychosocial adjustments that are usually not addressed by an ophthalmologist alone. The Ocular Genetics Program (OGP) at the Hospital for Sick Children, Toronto, was established in 1994 to provide comprehensive, multidisciplinary care of patients with inherited eye disorders. We now assess the benefits of such a program and of integrating research into the care of patients.

METHODS

We report our experience in developing a multidisciplinary ocular genetics program and the results of a pilot patient satisfaction survey that involved 61 patients.

RESULTS

The OGP multidisciplinary aspects are described. Of the 61 patients surveyed, 98% stated that they were satisfied with the OGP; 93%-96% of patients were content with "one day of appointments", "understanding of eye problem", and "coordination of ancillary tests such as visual fields test, electrophysiology, and others"; and for 70%-86% of respondents "waiting time to get an appointment", "information received on current research", and "primary health care provider adequately informed" were satisfactory.

INTERPRETATION

The OGP is a unique service in Canada, which strives to provide the comprehensive care needed by ocular genetic patients. High patient satisfaction is an indicator of the success of this approach. Long waiting times for appointments and application of laboratory research in clinical care remain challenging.

Novel RDH12 mutations associated with Leber congenital amaurosis and cone-rod dystrophy: biochemical and clinical evaluations

The purpose of this study was to determine the role of the retinol dehydrogenase 12 (RDH12) gene in patients affected with Leber congenital amaurosis (LCA), autosomal recessive retinitis pigmentosa (arRP) and autosomal dominant/recessive cone-rod dystrophies (CORD). Changes in the promoter region, coding regions and exon/intron junctions of the RDH12 gene were evaluated using direct DNA sequencing of patients affected with LCA (n=36 cases), RP (n=62) and CORD (n=21). The allele frequency of changes observed was assessed in a multiethnic control population (n=159 individuals). Detailed biochemical and structural modeling analysis of the observed mutations were performed to assess their biological role in the inactivation of Rdh12. A comprehensive clinical assessment of retinal structure and function in LCA patients carrying mutations in the RDH12 gene was completed. Of the six changes identified, three were novel including a homozygous C201R change in a patient affected with LCA, a heterozygous A177V change in patients affected with CORD and a heterozygous G46G change in a patient affected with LCA. A novel compound heterozygote T49M/A269fsX270 mutation was also found in a patient with LCA, and both homozygous and heterozygous R161Q changes were seen in 26 patients affected with LCA, CORD or RP. These R161Q, G46G and the A177V sequence changes were shown to be polymorphic. We found that Rdh12 mutant proteins associated with LCA were inactive or displayed only residual activity when expressed in COS-7 and Sf9 cells, whereas those mutants that were considered polymorphisms were fully active. Thus, impairment of retinal structure and function for patients carrying these mutations correlated with the biochemical properties of the mutants.

Assessment of Central Retinal Function in Patients with Advanced Retinitis Pigmentosa

PURPOSE

To assess central retinal function in patients with advanced retinitis pigmentosa (RP) using the multifocal (mf)ERG and static perimetry.

METHODS

Patients with RP; a nonrecordable, full-field (ff)ERG; and visual acuity (VA) of </= 1.0 logMAR were included. All patients underwent mfERG testing (103 hexagons, and 2.67 and 5.33 cd . s . m(-2) flash intensities) and static perimetry (103 corresponding areas) in the better eye. First-order kernel mfERGs were analyzed for total noise, signal-to-noise ratio, response amplitude, and implicit time. The number of areas with recordable mfERG responses were counted and compared with visual field (VF) sensitivity.

RESULTS

Twenty-nine patients aged 16 to 68 years with a VA of 0.02 to 1.0 logMAR and a kinetic VF of 10 degrees to 60 degrees in diameter were included. mfERGs were successfully performed in 22 of 29 patients. Responses were detected in at least one stimulated area in 22 of 22 patients, with an overall response detection of 9.8% in all stimulated areas and no difference between flash intensities. All responses were diminished severely in response density P1-N1, with normal P1 implicit time in 50% of the recordings. No predictive factors for recordable mfERG responses were identified. VF results were recorded reliably in 27 of 29 patients, with a 40% response detection rate.

CONCLUSIONS

mfERG responses were recordable in at least one area in all successfully tested patients with advanced RP. Response detection and performance was significantly higher for static perimetry. Static perimetry may be a more sensitive primary outcome measure of central vision function than the mfERG in patients with advanced RP and nonrecordable ffERGs.

Myocilin Gly252Arg mutation and glaucoma of intermediate severity in Caucasian individuals

OBJECTIVE

To determine the phenotype of an Australian pedigree with the myocilin (MYOC) Gly252Arg mutation, comparing it with other pedigrees carrying the same mutation.

METHODS

All recruited subjects underwent a comprehensive clinical examination, including optic disc assessment, applanation tonometry, and visual field measurement. Mutation analysis was performed through direct sequencing. Haplotype analysis was performed using microsatellite markers around the MYOC gene.

RESULTS

Eight Gly252Arg mutation carriers with glaucoma were identified from the same pedigree. Carriers' mean +/- SD age at diagnosis was 46.3 +/- 11.4 years (range, 31-60 years). Highest recorded intraocular pressure ranged from 27 to 42 mm Hg (mean +/- SD, 32.4 +/- 5.6 mm Hg). Cup-disc ratios in the worst eye ranged from 0.6 to 0.9. Six of the 8 individuals had undergone filtration surgery. A common founding haplotype between MY5 and D1S218 was found for Caucasian individuals tested with this mutation. One subject was compound heterozygotic for the MYOC Gly252Arg mutation and a novel MYOC Gly244Val variant.

CONCLUSIONS

Although a common founder for Gly252Arg across Caucasian subjects was found, the phenotype from this Australian MYOC mutation-carrying pedigree is less severe than previously described. The severity of glaucoma caused by the Gly252Arg mutation may be similar to the Thr377Met MYOC mutation, yet is more severe than the most common Gln368Stop mutation.

CLINICAL RELEVANCE

Since its implication in glaucoma, much work has been performed investigating the clinical features of MYOC-related glaucoma. Given the strong genotype-phenotype correlations with MYOC disease-causing variants, health care professionals armed with such molecular information are able to accurately counsel patients on their likely disease course. Our work suggests that the disease associated with MYOC Gly252Arg is less severe than previously described in other pedigrees with this specific mutation.

CRYBA4, a novel human cataract gene, is also involved in microphthalmia

Genetic analysis of a large Indian family with an autosomal dominant cataract phenotype allowed us to identify a novel cataract gene, CRYBA4. After a genomewide screen, linkage analysis identified a maximum LOD score of 3.20 (recombination fraction [theta] 0.001) with marker D22S1167 of the beta -crystallin gene cluster on chromosome 22. To date, CRYBA4 was the only gene in this cluster not associated with either human or murine cataracts. A pathogenic mutation was identified in exon 4 that segregated with the disease status. The c.317T-->C sequence change is predicted to replace the highly conserved hydrophobic amino acid phenylalanine94 with the hydrophilic amino acid serine. Modeling suggests that this substitution would significantly reduce the intrinsic stability of the crystalline monomer, which would impair its ability to form the association modes critical for lens transparency. Considering that CRYBA4 associates with CRYBB2 and that the latter protein has been implicated in microphthalmia, mutational analysis of CRYBA4 was performed in 32 patients affected with microphthalmia (small eye). We identified a c.242T-->C (Leu69Pro) sequence change in exon 4 in one patient, which is predicted here to disrupt the beta -sheet structure in CRYBA4. Protein folding would consequently be impaired, most probably leading to a structure with reduced stability in the mutant. This is the first report linking mutations in CRYBA4 to cataractogenesis and microphthalmia.