Analysis of predictors of success in the MRCP (UK) PACES examination in candidates attending a revision course.

OBJECTIVE: To determine factors that predict success of candidates taking a revision course in preparation for the MRCP (UK) PACES (practical assessment of clinical examination skills) examination. DESIGN: A questionnaire survey of candidates attending a PACES revision course. Results were correlated with subsequent pass lists published by the Colleges of Physicians. SETTING AND SUBJECTS: Candidates attending courses in June and October 2002. In total, 523 candidates completed questionnaires, evenly balanced between UK and overseas graduates. RESULTS: Of 483 candidates who took the examination immediately after the course, 219 (45.3%) passed. UK graduates were more likely to pass (67.0%) than overseas graduates (26.2%) (p = 0.003, odds ratio 5.72). For UK graduates, pass rates were higher for white candidates (73%) than for ethnic minorities (56%) (p = 0.012, OR 2.15) and for those who passed at the first attempt in the MRCP (UK) part 2 written paper (p = 0.003, OR 2.90). For overseas graduates, those who had been qualified for less than eight years were more likely to pass (p = 0.001, OR 2.78). More overseas (45.7%) than UK (30.8%) graduates were confident that they would pass, but confidence did not predict success. CONCLUSION: Among candidates taking a revision course, UK graduates are more likely to pass the PACES examination than non-UK graduates. Ethnic minority UK graduates seem to have a significantly poorer success rate, although this requires confirmation in an independent sample. If confirmed, these differences merit further investigation to assess whether they reflect genuine differences in ability.

A new locus for autosomal recessive RP (RP29) mapping to chromosome 4q32-q34 in a Pakistani family.

PURPOSE: To map the disease locus in a six-generation, consanguineous Pakistani family with autosomal recessive retinitis pigmentosa (arRP). All affected individuals had pigmentary retinopathy associated with symptoms of night blindness and the loss of peripheral visual fields by the age of 20 years, loss of central vision between the ages of 25 and 30 years, and complete blindness between the ages of 40 and 50 years. METHODS: Genomic DNA from family members was typed for alleles at known polymorphic genetic markers using polymerase chain reaction. Alleles were assigned to individuals, which allowed calculation of LOD scores using the programs Cyrillic (http://www.cyrillicsoftware.com) and MLINK (Cherwell Scientific Publishing LTD:, Oxford, UK). The genes for membrane glycoprotein (M6a) and chloride channel 3 (CLCN3) were analyzed by direct sequencing for mutations. RESULTS: A new locus for arRP (RP29) has been mapped to chromosome 4q32-q34. A maximum two-point LOD score of 3.76 was obtained for the marker D4S415, with no recombination. Two recombination events in the pedigree positioned this locus to a region flanked by markers D4S621 and D4S2417. A putative region of homozygosity by descent was observed between the loci D4S3035 and D4S2417, giving a probable disease interval of 4.6 cM. Mutation screening of two candidate genes, M6a and CLCN3, revealed no disease-associated mutations. CONCLUSIONS: The results suggest that the arRP phenotype maps to a new locus and is due to a mutated gene within the 4q32-q34 chromosomal region.

Molecular genetics and prospects for therapy of the inherited retinal dystrophies.

More than 60 genes responsible for human retinal dystrophies have been identified. Those recently isolated include the transcription factor genes NRL and NR2E3, RDH5 (retinol dehydrogenase), EFEMP1 (which encodes an extracellular matrix protein), CRB1, PROML1, RP1, AIPL1 and USH1C (harmonin). The ABCR protein has been identified as a critical transporter in the recycling of retinal (vitamin A). At present, a number of novel therapeutic strategies are being evaluated including pharmacological treatments, cell transplantation and gene therapy. The progress made with such approaches now offers hope to patients with these incurable forms of blindness.

Spectrum of mutations in USH2A in British patients with Usher syndrome type II.

Usher syndrome (USH) is a combination of a progressive pigmentary retinopathy, indistinguishable from retinitis pigmentosa, and some degree of sensorineural hearing loss. USH can be subdivided in Usher type I (USHI), type II (USHII) and type III (USHIII), all of which are inherited as autosomal recessive traits. The three subtypes are genetically heterogeneous, with six loci so far identified for USHI, three for USHII and only one for USHIII. Mutations in a novel gene, USH2A, encoding the protein usherin, have recently been shown to be associated with USHII. The gene encodes a protein with partial sequence homology to both laminin epidermal growth factor and fibronectin motifs. We analysed 35 British and one Pakistani Usher type II families with at least one affected member, for sequence changes in the 20 translated exons of the USH2A gene, using heteroduplex analysis and sequencing. Probable disease-causing mutations in USH2A were identified in 15 of 36 (41.7%) Usher II families. The most frequently encountered mutation (11/15 families or 11/18 mutated alleles) was del2299G in exon 13, resulting in a frameshift and premature stop codon. Other mutations include insertions and point mutations, of which two are previously unreported. Five different polymorphisms were also detected. Our results indicate that mutations in this gene are responsible for disease in a large proportion of British Usher type II patients. Moreover, if screening for mutations in USH2A is considered, it is sensible to screen for the del2299G mutation first.

NRL S50T mutation and the importance of 'founder effects' in inherited retinal dystrophies.

The aim of this work was to identify NRL mutations in a panel of 200 autosomal dominant retinitis pigmentosa (adRP) families. All samples were subjected to heteroduplex analysis of the three exons of the NRL gene, and HphI restriction digest analysis of exon 2 (to identify the S50T mutation). Families found to have the S50T mutation, and six additional larger pedigrees (which had previously been excluded from the other nine adRP loci) underwent linkage analysis using polymorphic markers located in the region of 14q11. HphI restriction analysis followed by direct sequencing of the amplified NRL exon 2 product demonstrated the presence of the NRL S50T sequence change in three adRP families. Comparison of marker haplotypes in affected individuals from these families with those of affected members of the original 14q11 linked family revealed a common disease haplotype for markers within the adRP locus. Recombination events observed in these families define an adRP critical interval of 14.9 cM between D13S72 and D14S1041. Linkage analysis enabled all six of the larger adRP pedigrees to be excluded from the 14q11 locus. The NRL S50T mutation represents another example of a 'founder effect' in a dominantly inherited retinal dystrophy. Identification of such 'founder effects' may greatly simplify diagnostic genetic screening and lead to better prognostic counselling. The exclusion of several adRP families from all ten adRP loci indicates that at least one further adRP locus remains to be found.

An analysis of ABCR mutations in British patients with recessive retinal dystrophies.

PURPOSE: Several reports have shown that mutations in the ABCR gene can lead to Stargardt disease (STGD)/fundus flavimaculatus (FFM), autosomal recessive retinitis pigmentosa (arRP), and autosomal recessive cone-rod dystrophy (arCRD). To assess the involvement of ABCR in these retinal dystrophies, the gene was screened in a panel of 70 patients of British origin. METHODS: Fifty-six patients exhibiting the STGD/FFM phenotype, 6 with arRP, and 8 with arCRD, were screened for mutations in the 50 exons of the ABCR gene by heteroduplex analysis and direct sequencing. Microsatellite marker haplotyping was used to determine ancestry. RESULTS: In the 70 patients analyzed, 31 sequence changes were identified, of which 20 were considered to be novel mutations, in a variety of phenotypes. An identical haplotype was associated with the same pair of in-cis alterations in 5 seemingly unrelated patients and their affected siblings with STGD/FFM. Four of the aforementioned patients were found to carry three alterations in the coding sequence of the ABCR gene, with two of them being in-cis. CONCLUSIONS: These results suggest that ABCR is a relatively polymorphic gene. Because putative mutations have been identified thus far only in 25 of 70 patients, of whom only 8 are compound heterozygotes, a large number of mutations have yet to be ascertained. The disease haplotype seen in the 5 patients carrying the same "complex" allele is consistent with the presence of a common ancestor.

Genetic analysis of the guanylate cyclase activator 1B (GUCA1B) gene in patients with autosomal dominant retinal dystrophies.

The guanylate cyclase activator proteins (GCAP1 and GCAP2) are calcium binding proteins which by activating Ret-GC1 play a key role in the recovery phase of phototransduction. Recently a mutation in the GUCA1A gene (coding for GCAP1) mapping to the 6p21.1 region was described as causing cone dystrophy in a British family. In addition mutations in Ret-GC1 have been shown to cause Leber congenital amaurosis and cone-rod dystrophy. To determine whether GCAP2 is involved in dominant retinal degenerative diseases, the GCAP2 gene was screened in 400 unrelated subjects with autosomal dominant central and peripheral retinal dystrophies. A number of changes involving the intronic as well as the coding sequence were observed. In exon 1 a T to C nucleotide change was observed leaving the tyrosine residue 57 unchanged. In exon 3 a 1 bp intronic insertion, a single nucleotide substitution G to A in the intron 3' of this exon, and a GAG to GAT change at codon 155 were observed. This latter change results in a conservative change of glutamic acid to aspartic acid. In exon 4 a 7 bp intronic insertion, a single nucleotide A to G substitution in the intron 5' of this exon, and a single base pair change C to G in the intron 3' of exon 4 were seen. None of these changes would be expected to affect correct splicing of this gene. All these changes were observed in controls. The results of this study do not show any evidence so far that GCAP2 is involved in the pathogenesis of autosomal dominant retinal degeneration in this group of patients. All the changes detected were found to be sequence variations or polymorphisms and not disease causing.

Clinical features of codon 172 RDS macular dystrophy: similar phenotype in 12 families.

OBJECTIVE: To report the phenotype associated with the codon 172 RDS (gene for retinal degeneration slow) mutation in 11 separate families with an arginine-to-tryptophan substitution with common ancestry, and 1 family with an arginine-to-glutamine transition. PATIENTS: Screening for RDS gene mutations was performed in 400 subjects with autosomal dominant retinal degeneration. Twelve families were identified with a mutation in codon 172. Haplotype analysis was performed. Full ophthalmic evaluation was performed, including electrophysiologic and psychophysical investigation and imaging of autofluorescence using confocal laser scanning ophthalmoscopy. RESULTS: Haplotype analysis demonstrated that the 11 families were ancestrally related. All 12 families showed a common phenotype of macular dysfunction, with the deficit increasing with age. Abnormally high autofluorescence predated loss of visual acuity or visual field changes. Pattern electroretinographic (PERG) findings were affected early in disease. There was high intrafamilial and interfamilial consistency of phenotype. CONCLUSION: These families demonstrate a striking conformity of symptoms and signs. CLINICAL RELEVANCE: In the codon 172 RDS mutation, unlike disease resulting from other RDS mutations, prediction of approximate age of onset and progression of visual deficit is possible. This should assist diagnosis and counseling.

Phenotype of autosomal recessive congenital microphthalmia mapping to chromosome 14q32.

BACKGROUND: Congenital microphthalmia (OMIM: 309700) may occur in isolation or in association with a variety of systemic malformations. Isolated microphthalmia may be inherited as an autosomal dominant, an autosomal recessive, or an X linked trait. METHODS: Based on a whole genome linkage analysis, in a six generation consanguineous family with autosomal recessive inheritance, the first locus for isolated microphthalmia was mapped to chromosome 14q32. Eight members of this family underwent clinical examination to determine the nature of the microphthalmia phenotype associated with this locus. RESULTS: All affected individuals in this family suffered from bilateral microphthalmia in association with anterior segment abnormalities, and the best visual acuity achieved was "perception of light". Corneal changes included partial or complete congenital sclerocornea, and the later development of corneal vascularisation and anterior staphyloma. Intraocular pressure, as measured by Schiotz tonometry, was greatly elevated in many cases. CONCLUSIONS: This combination of ocular defects suggests an embryological disorder involving tissues derived from both the neuroectoderm and neural crest. Other families with defects in the microphthalmia gene located on 14q32 may have a similar ocular phenotype aiding their identification.

Severe autosomal dominant retinitis pigmentosa caused by a novel rhodopsin mutation (Ter349Glu). Mutations in brief no. 208. Online.

Mutations in the rhodopsin gene are reported to be responsible for approximately 25% of all cases of autosomal dominant Retinitis pigmentosa (adRP). Affected individuals from a large family with an unusually severe form of adRP were screened for mutations in the rhodopsin gene. Direct sequencing of exon 5 revealed a TAA to GAA transversion at nucleotide 5276/codon 349, which was confirmed by Dde1 restriction digest analysis. This change would replace the normal termination codon with a glutamic acid residue (Ter-349-Glu, or X349E). The next predicted termination codon (TAA) lies 153bp downstream at nucleotides 5429 to 5431. Termination of transcription at this point would add an additional 51 amino-acid residues to the carboxy terminus of the rhodopsin molecule. This mutation is unique in producing a mutant rhodopsin in which all of the normal 348 amino-acid residues remain intact. It produces one of the most severe adRP phenotypes ever observed in a family with a rhodopsin mutation. In view of this the Ter-349-Glu mutation is worthy of further investigation to determine how the presence of this particular mutant opsin leads to rod photoreceptor degeneration.

The management of dislocated lens material after phacoemulsification.

PURPOSE: To determine the visual outcome, prognostic factors, and effect of timing of surgical intervention in patients with retained lens fragments after phacoemulsification. METHODS: A retrospective review was carried out of the notes of 44 consecutive patients who suffered posterior dislocation of lens fragments during phacoemulsification, of whom 34 underwent vitrectomy. RESULTS: The presence of severe uveitis at presentation was a significant predictor of a final visual acuity of less than 6/60 (p = 0.002). A raised intraocular pressure at presentation (> 29 mmHg) significantly increased the risk of chronic glaucoma (p = 0.0279), but there was no association between glaucoma and delay in vitrectomy. Patients operated on within 1 week of cataract surgery obtained a better visual outcome (64.7%) of patients achieved 6/12 or better visual acuity) than those operated on later than 1 week (41% obtained 6/12), but this difference did not reach statistical significance. CONCLUSIONS: The trend towards a better visual outcome with early vitrectomy was not statistically significant. A large prospective trial is indicated to determine the optimum time for vitrectomy in these patients.

Further refinement of the Usher 2A locus at 1q41.

Usher syndrome (USH) is characterised by congenital sensorineural hearing loss and progressive pigmentary retinopathy. All three subtypes (USH1, USH2, and USH3) are inherited as recessive traits. People with Usher type 2 (USH2) have normal vestibular responses and moderate to severe hearing loss. These syndromes have been found to be genetically heterogeneous, with a single locus for USH2 at 1q41 (USH2A), six loci for USH1, and one for USH3. Some USH2 families have been excluded from the 1q41 locus suggesting that a second, as yet unidentified, locus (USH2B) must exist. Linkage studies suggest that around 90% of USH2 families are USH2A. Four USH2 families were analysed for linkage to markers flanking the USH2A locus. In one of these families a recombination event was observed in an affected subject which excludes the USH2A gene from proximal to the marker AFM143XF10 and defines this as the new centromeric flanking marker for the USH2A locus. A further recombination event in another patient from this family confirmed AFM144XF2 as the telomeric flanking marker. The interval between these polymorphic markers is estimated to be 400 kb. This region is completely contained in each of three YACs from the CEPH library: 867g9, 919h3, and 848b9. This refinement more than halves the critical genetic interval and will greatly facilitate positional cloning of the USH2A gene.

A new family of Greek origin maps to the CRD locus for autosomal dominant cone-rod dystrophy on 19q.

Retinal photoreceptor dystrophies (RD) are a highly heterogeneous group of genetic disorders of the retina, representing the most frequently inherited form of visual handicap, affecting approximately 1.5 million people world wide. To date, more than 40 genetic loci have been implicated in RD. One of them, the CORD2 locus, for an autosomal dominant form of cone-rod dystrophy (CRD), maps to chromosome 19q and has previously been reported in a single large family of British origin. We now report a new family with severe early onset CRD, phenotypically very similar to the British family, which also maps to 19q, but is of Greek origin. Haplotype data of the Greek family showed no recombination between and including markers D19S219 and D19S246 and linkage analysis gave a lod score of 2.7 (at theta=0) with marker D19S412, confirming the data obtained in the British family.

A locus for autosomal recessive congenital microphthalmia maps to chromosome 14q32.

Congenital microphthalmia (CMIC) (OMIM 309700) may occur in isolation or in association with a variety of systemic malformations. Isolated CMIC may be inherited as an autosomal dominant, an autosomal recessive, or an X-linked trait. On the basis of a whole-genome linkage analysis, we have mapped the first locus for isolated CMIC, in a five-generation consanguineous family with autosomal recessive inheritance, to chromosome 14q32. All affected individuals in this family have bilateral CMIC. Linkage analysis gave a maximum two-point LOD score of 3.55 for the marker D14S65. Surrounding this marker is a region of homozygosity of 7.3 cM, between the markers D14S987 and D14S267, within which the disease gene is predicted to lie. The genes for several eye-specific transcription factors are located on human chromosome 14q and in the syntenic region of mouse chromosome 12. However, both CHX10 (14q24.3), mutations of which give rise to CMIC in mouse models, and OTX2 (14q21-22) can be excluded as candidates for autosomal recessive congenital microphthalmia (arCMIC), since they map outside the critical disease region defined by recombination events. This suggests that arCMIC is caused by defects in a novel developmental gene that may be important or even essential in eye development.

Epithelial debridement for secondary hyperopia following myopic excimer laser photorefractive keratectomy.

BACKGROUND: To evaluate epithelial debridement for the treatment of persistent hyperopia in eyes that had photorefractive keratectomy (PRK). SETTING: Optimax Laser Eye Clinics, Manchester, London, Bristol, England. METHODS: Epithelial debridement was performed on 46 eyes to reduce the hypermetropia following excimer laser PRK. RESULTS: Mean age of the patients was 43 years +/- 9.7 (SD). Mean refractive change was -0.51 diopter (D) +/- 0.76 (range +0.75 to -2.50 D). Mean change in best corrected visual acuity (BCVA) was 0.00 Logmar units (range +0.40 to -0.20 units), although 33% of eyes lost one line or more of Logmar BCVA. Mean follow-up after debridement was 61.0 +/- 26.9 weeks (range 26 to 140 weeks). CONCLUSIONS: Epithelial debridement is an unpredictable procedure to treat secondary hyperopia after PRK, producing a small mean change in spherical equivalent with a wide range of results. A significant number of eyes lost one line or more of Logmar BCVA. We therefore do not advocate epithelial debridement after PRK.