Should a standard be defined for the Positive Predictive Value (PPV) of recall in the UK NHS Breast Screening Programme?

The UK NHSBSP defines standards for both cancer detection rate and recall rate for assessment but has not explicitly set a defined standard for positive predictive value (PPV) of recall. However, as PPV is defined as the percentage of women who are recalled and have a final diagnosis of cancer, a standard for PPV is an implicit consequence of the standards for cancer detection rate and recall rate. The standards are defined in terms of a lower level of acceptability known as the 'minimum standard' and a higher level of acceptability referred to as the 'target'. The target can be shown to be a PPV of more than 5.1% for prevalent screens and more than 8.4% for incident screens. This paper will explore the role of PPV as a performance measure and show how making moderate increases in PPV for programmes with the lowest PPVs could lead to major improvements in the overall efficiency of the programme.

Is radiologists' volume of mammography reading related to accuracy? A critical review of the literature

The current UK quality assurance guidelines for radiologists in the NHS breast screening programme require those reporting screening mammograms to read a minimum of 5000 cases per year. We aimed to review the evidence for this and to assess whether there was justification for lowering the required level. A literature search was conducted to identify relevant studies where accuracy of reporting mammograms was related to reading volume. Three of the five studies reviewed suggested a positive association between reading volume and sensitivity, but there were few data on volumes above 5000 cases per year. The available evidence did not provide any basis for reducing the threshold volume. Further work is needed, in a UK or European setting, to study the relationship between reading volume and accuracy at higher volume levels and also the separate effects of reading volume and reading experience.

The effect of changing from one to two views at incident (subsequent) screens in the NHS breast screening programme in England: impact on cancer detection and recall rates

AIM

To assess the effect on cancer detection and recall rates of changing from one to two views for incident (subsequent) screens.

METHODS

Controlled, comparative, observational study of programmes in NHS breast screening programme in England.

SUBJECTS

women aged 50-64 years were screened by the NHSBSP between 1 April 2001 and 31 March 2003.

RESULTS

The effect of changing to two-view mammography was a 20% increase in overall incident screen cancer detection rate, with the biggest effect seen for small (<15 mm) invasive cancers. This increased detection rate was achieved with an 11% drop-in recall rate.

CONCLUSION

The introduction of two-view mammography for incident screens has resulted in considerable improvements in overall NHS breast screening performance.

Serine 18 phosphorylation of RAX, the PKR activator, is required for PKR activation and consequent translation inhibition

It is now apparent that the double-stranded (ds)RNA-dependent protein kinase, PKR, is a regulator of diverse cellular responses to stress. Recently, the murine dsRNA-binding protein RAX and its human ortholog PACT were identified as cellular activators of PKR. Previous reports demonstrate that following stress, RAX/PACT associates with and activates PKR resulting in eIF2alpha phosphorylation, consequent translation inhibition, and cell death via apoptosis. Although RAX/PACT is phosphorylated during stress, any regulatory role for this post-translational modification has been uncertain. Now we have discovered that RAX is phosphorylated on serine 18 in both human and mouse cells. The non-phosphorylatable form of RAX, RAX(S18A), although still able to bind dsRNA and associate with PKR, fails to activate PKR following stress. Furthermore, stable expression of RAX(S18A) results in a dominant-negative effect characterized by deficiency of eukaryotic initiation factor 2 alpha subunit phosphorylation, delay of translation inhibition, and failure to undergo rapid apoptosis following removal of interleukin-3. We propose that the ability of RAX to activate PKR is regulated by a sequential mechanism featuring RAX association with PKR, RAX phosphorylation at serine 18, and activation of PKR.

Spatial variation of refractive index in a pane of float glass

In the statistical interpretation of forensic glass evidence it is standard practice to make the assumption of homogeneity of the refractive index (RI) of the source glass, or of localized homogeneity. However, the work of Locke and Hayes showed that, for toughened windscreen glass, this assumption might not be true. This work is well cited, but there appears to have been little follow-on published research. Furthermore, the toughening process is something known to affect the refractive index, and is a process that float glass does not undergo. Float glass is a major component of casework in New Zealand and for that reason it would be interesting to know whether the findings of Locke and Hayes apply when dealing with float glass. In this paper we describe an experiment similar to that of Locke and Hayes, systematically examining the variation of RI in a pane of float window glass. It was found that, although there were no systematic differences in refractive index, there were observable differences across the pane.

Does individual programme size affect screening performance? Results from the United Kingdom NHS breast screening programme

OBJECTIVE

The size (number of women screened) of the 95 individual NHS breast screening programmes (NHSBSPs) varies by a factor of 10. This study investigates the impact of size on the performance of individual programmes.

METHOD

Data were collated from the 95 United Kingdom screening programmes on the standard statistical returns for the past 5 years (1 April 1995-31 March 2000). Additional information was obtained from questionnaires. The number of women screened between 1 April 1999 and 31 March 2000 determined the size of a programme. The bottom 25% were defined as small, the middle 50% as medium, and the top 25% as large. On average large programmes screened about four times as many women as small programmes and medium programmes about twice as many. Performance was evaluated using cancer detection rates, referral rates for assessment, and positive predictive value (PPV) of assessment using PPV referral diagrams.

RESULTS

The performance of smaller programmes was shown to be marginally poorer than medium and large sized programmes in that they detected fewer cancers and had a lower PPV. The smallest 25% of programmes had an invasive cancer detection rate 13% less than the medium and large programmes. However, if these programmes had an equivalent detection rate to the medium/large programmes the national detection rate would only increase by about 2%. This is because the 75% of programmes described as medium and large screen about 90% of all women. It is therefore important to place the clinical importance of these findings in context when considering any envisaged possible solutions.

CONCLUSIONS

Although the performance of smaller programmes was shown to be poorer than that of the larger programmes, it is not clear from this study exactly why this is so. A likely contributory factor based on experience of evaluating the NHSBSP is that performance problems in larger programmes have been easier to detect by quality assurance staff. The size of the small programmes and the few screen detected cancers (and inherent statistical instability in detection rates) mean that problems are difficult to identify. As a consequence small programmes which are genuinely performing marginally below specific standards are likely to receive less attention than larger programmes, and even under close scrutiny the causes are less likely to be found.

A RecA homologue in Ustilago maydis that is distinct and evolutionarily distant from Rad51 actively promotes DNA pairing reactions in the absence of auxiliary factors

Two RecA homologues have been identified to date in Ustilago maydis. One is orthologous to Rad51 while the other, Rec2, is structurally quite divergent and evolutionarily distant. DNA repair and recombination proficiency in U. maydis requires both Rec2 and Rad51. Here we have examined biochemical activities of Rec2 protein purified after overexpression of the cloned gene. Rec2 requires DNA as a cofactor to hydrolyze ATP and depends on ATP to promote homologous pairing and DNA strand exchange. ATPgammaS was found to substitute for ATP in all pairing reactions examined. With superhelical DNA and a homologous single-stranded oligonucleotide as substrates, Rec2 actively promoted formation and dissociation of D-loops. When an RNA oligonucleotide was substituted it was found that R-loops could also be formed and utilized as primer/template for limited DNA synthesis. In DNA strand exchange reactions using oligonucleotides, we found that Rec2 exhibited a pairing bias that is opposite that of RecA. Single-stranded oligonucleotides were activated for DNA strand exchange when attached as tails protruding from a duplex sequence due to enhanced binding of Rec2. The results indicate that Rec2 is competent, and in certain ways even better than Rad51, in the ability to provide the fundamental DNA pairing activity necessary for recombinational repair. We propose that the emerging paradigm for homologous recombination featuring Rad51 as the essential catalytic component for strand exchange may not be universal in eukaryotes.

Pedigree parables

Pedigrees are a foundation of genetic counseling and human genetic research. To protect patient/subject and family privacy and confidentiality it is not unusual to find published pedigrees that have been masked (i.e. a pedigree that has been changed in ways that are obvious to the reader such as diamonds to mask gender) or altered (i.e. changing pedigree information in ways that are not obvious to the reader such as changing gender and birth order or deleting unaffected siblings from the pedigree). Failure to report pedigree data (e.g. omitting ages, ethnicity, etc.) is another measure used to protect subject and family confidentiality. At what point do such practices hinder the recognition of genetic processes? Is there evidence that harm has occurred to subjects who have appeared in published pedigrees? How does the researcher or clinician determine which information is essential to record on the pedigree? The author uses a historical perspective and case examples to illustrate the issues of balancing protection of the genetic subject's privacy with the reporting of unaltered family data. The author presents several critical questions for peer reviewers and investigators to consider when a pedigree is included in a manuscript, or for researchers involved in family studies.

Fibrinogen bellingham: a gamma-chain R275C substitution and a beta-promoter polymorphism in a thrombotic member of an asymptomatic family

Congenital dysfibrinogenemia is a rare cause of unexplained thrombosis. However, most individuals with dysfibrinogenemia are asymptomatic, suggesting that co-morbid factors contribute to thrombo-embolic events. The potential roles of additional genetic or acquired prothrombotic risk factors are poorly understood because detailed family studies are lacking. Herein, we describe a family whose propositus was a young Caucasian man with recurrent venous thrombo-emboli and dysfibrinogenemia due to heterozygosity for an Arg-->Cys substitution at residue 275 in the gamma-chain. The only additional thrombophilic abnormality found in the proband was heterozygosity for a G/A transition at position -455 in the fibrinogen beta-chain promoter; a genotype associated with high acute phase levels of fibrinogen. The proband's father, who died of a cerebral artery thrombosis, carried the gammaR275C substitution but not the beta-promoter -455 variant. Among 14 living relatives, eight were heterozygous for one or the other mutation and only one, a 21-year-old niece, was dually affected. None had suffered bleeding or thrombosis. In vitro studies of the proband's purified fibrinogen revealed markedly abnormal thrombin-catalyzed polymerization and delayed fibrin clot lysis by tPA-activated plasmin. We hypothesize that the gammaR275C substitution predisposes to thrombosis by generating clots that are relatively resistant to fibrinolysis. The clinical risk is low, however, in the absence of an additional thrombophilic mutation. The beta-promoter variant could, theoretically, contribute to this risk by augmenting expression of the dysfibrinogen under conditions of stress. Like the common hereditary thrombophilias, heterozygous familial dysfibrinogenemia induces thrombosis in the setting of multiple prothrombotic influences.

Additional kinematic variables to describe differences in the trot between clinically normal dogs and dogs with hip dysplasia

OBJECTIVE

To describe the abnormal gait of dogs with hip dysplasia by use of kinematic gait analysis.

ANIMALS

19 large-breed dogs with moderate to severe clinical and radiographic evidence of hip dysplasia and 10 clinically normal dogs (controls).

PROCEDURE

Kinematic and force plate data were collected, and degree of coxofemoral joint abduction-adduction, mediolateral foot movement, distance between hind feet, maximum hind foot elevation, mediolateral pelvic movement, and coxofemoral joint angular acceleration were calculated. Essential Fourier coefficients were determined and used to reconstruct mean angular acceleration curves. Fourier coefficients and foot and pelvic movement data were compared between groups.

RESULTS

Dogs with hip dysplasia had a greater degree of coxofemoral joint adduction and range of abduction-adduction and greater lateral pelvic movement, compared with controls. Foot movement variables did not differ significantly between groups. Coxofemoral joint angular acceleration was greater in the middle to end of the stance phase, whereas deceleration was greater in the late stance to early swing phase and middle to end of the swing phase in dogs with hip dysplasia, compared with controls.

CONCLUSIONS AND CLINICAL RELEVANCE

Differences in degree of coxofemoral joint abduction-adduction, amount of mediolateral pelvic movement, and coxofemoral joint angular acceleration between clinically normal dogs and dogs with hip dysplasia may indicate a compensation in gait of affected dogs as a result of discomfort or biomechanical effects attributable to hip dysplasia and degenerative joint disease. Information gained from kinematic and kinetic gait analyses may be useful in evaluating treatments for hip dysplasia in dogs.

Distinct roles of the homeotic genes Ubx and abd-A in beetle embryonic abdominal appendage development

Insects are easily distinguishable by the absence of legs on the adult abdomen. Studies performed on the Dipteran, Drosophila melanogaster, indicate that this is because of the repressive effects of the homeotic genes Ultrabithorax (Ubx) and abdominal-A (abd-A) on the limb promoting gene Distal-less (Dll) during embryonic development. However, in many species appendage-like structures are present on abdominal segments in embryonic and juvenile stages. Here, by using classical genetics and double-stranded RNA-mediated gene silencing in the red flour beetle, Tribolium castaneum, a species that develops an appendage on the first abdominal segment, we investigate the roles of Ubx and Abd-A in abdominal limb development. We find that in Tribolium, Abd-A, but not Ubx, represses early expression of Dll in the embryonic abdomen. Ubx appears to modify the A1 appendage. This difference in the activities of Abd-A and Ubx is critical for proper development of this appendage. We suggest that an ancestral role of Abd-A in insect abdominal appendage development was in the repression of Dll initiation and that of Ubx was in modulation of abdominal appendage morphology.

Molecular and genetic analysis of the Tribolium Ultrabithorax ortholog, Ultrathorax

Ultrabithorax (Ubx) is essential for the proper patterning of the posterior thorax and anterior abdomen in Drosophila. The Coleoptera and Diptera differ in the organization and structure of their thorax and anterior abdomen. Changes in the regulation of Ubx and/or its downstream target genes are predicted to underlie these altered morphologies. We exploited the feasibility of genetic analysis in the red flour beetle, Tribolium castaneum, to examine the role of its Ubx ortholog in development. We analyzed genomic and cDNA clones that predict a polypeptide with nearly 100% identity with the Drosophila Ubx gene in the homeodomain and flanking sequences. Southern blot analysis indicates that these clones represent DNA sequences within the Homeotic complex (HOM-C) of Tribolium. Phenotypic analysis of mutant variants of the Ultrathorax (Utx) gene, and its location within the beetle HOM-C, strongly supports Utx being the Tribolium ortholog of Ubx. The embryonic expression pattern of Ubx-homologous transcripts coincides with the phenotypes associated with Utx mutations, providing support that the Ubx-homologous cloned DNA represents the Utx locus. By mid-germband extension Utx transcripts are expressed in a pattern similar to Ubx in Drosophila. However, during early germband formation Utx transcripts differ in both spatial and temporal progression. Utx expression is initially detected in parasegments 4 and 5 (T1p-T3a) as they are established during early germband formation. This is the first report of the wild-type parasegmental expression of an insect Ubx ortholog extending through parasegment 4. The earlier and more anterior expression in the thorax may underlie the modification of the Coleopteran thorax.

Inconsistencies in genetic counseling and screening for consanguineous couples and their offspring: the need for practice guidelines

PURPOSE

To determine current practices of genetic counseling and screening for consanguineous couples, their pregnancies and children, and to compare these practices to recommendations in the literature.

METHODS

A questionnaire was mailed to 1,582 board certified genetic counselors and medical geneticists in the United States.

RESULTS

The return rate was 20% (n = 309). There was wide variation in the risk figures quoted to consanguineous couples to have offspring with birth defects and mental retardation (1% to 75% for incest between first-degree relatives, and 0.25% to 20% for first cousin unions). Suggested screening practices differed for consanguineous unions before conception, during pregnancy, following birth, and for children placed for adoption. Most respondents recommended screening based on ethnicity, yet disagreed as to which genetic disorders to include.

CONCLUSIONS

To standardize genetic services, guidelines for screening the offspring of consanguineous unions are needed. A consensus should be reached as to the empirical risks for genetic disorders, birth defects, and mental retardation that may impair the offspring of consanguineous unions, with definition as to what these disorders are, and if the data applies to global populations. Guidelines should consider costs, the sensitivity and specificity of DNA and biochemical testing, and current practices of prenatal and newborn screening. Consideration should be given to screening based on ethnicity, particularly in populations where consanguineous unions are common, while remaining sensitive to cultural belief systems. Recommendations for screening healthy children from consanguineous unions to be placed for adoption pose ethical challenges.

Racial variation in the use of laparoscopic cholecystectomy in the Department of Veterans Affairs medical system

BACKGROUND

While studies have found racial differences in the rates of use of established invasive cardiac and cerebrovascular procedures, no study has evaluated racial variation in the rates of adoption of new surgical procedures. For patients undergoing laparoscopic cholecystectomy, the procedure represents a new and safe option that shortens the duration of postoperative hospitalization by almost one week. In this study, we evaluated whether, in the equal access Veterans Affairs (VA) medical system, the rate of adoption of this procedure and improvements in the duration of postoperative hospitalization differed between African-American and Caucasian patients.

STUDY DESIGN

Data were obtained from two sources-administrative claims files and prospectively compiled dinical data from medical records and patient interviews. In both data sets, frequency of use, length of stay, and outcomes for African-American and Caucasian patients undergoing minimally invasive and open gallbladder surgery were analyzed for the first four years of use of the procedure in the VA system (1992 to 1995).

RESULTS

Analyses based on claims files indicated that, after adjustment for potentially confounding variables, African-American patients who underwent cholecystectomy in VA medical centers were 25% less likely to undergo a minimally invasive cholecystectomy during the first 4 years of use of the new procedure (adjusted odds ratio, 0.74; 95% confidence interval, 0.66-0.83). Shortening of the average postoperative length of stay from 9 days or more in the prelaparoscopic era to less than 4.5 days for patients undergoing the laparoscopic procedure occurred in the first year for Caucasian patients, but did not occur until the fourth year for African-American patients (p<0.001). The overall difference in postoperative length of stay between African-American and Caucasian patients more than doubled from 1.7 days before introduction of laparoscopic cholecystectomy to 3.8 days in the fourth year. In comparison, analyses based on nurse-compiled clinical data indicated that, after adjustment for relevant clinical factors, racial variations in the rate of laparoscopic surgery were even larger (adjusted odds ratio for laparoscopic versus open cholecystectomy for African-American versus Caucasian veterans, 0.68; 95% confidence interval, 0.55-0.84).

CONCLUSIONS

Compared to Caucasian patients, African-American patients who underwent cholecystectomy in VA medical centers had an approximately 25% to 32% lower likelihood of undergoing minimally invasive cholecystectomy procedures. The differences in rates of adoption of laparoscopic surgery did not appear to be from more comorbid illnesses among African-American patients. African-American and Caucasian veterans may differ in their preference for new surgical procedures like laparoscopic cholecystectomy. Conversely, VA physicians may have been less likely to recommend laparoscopic cholecystectomies to African-American patients.

Diffusion of laparoscopic cholecystectomy in the Veterans Affairs health care system, 1991-1995

CONTEXT

Laparoscopic cholecystectomy has become the most widely used treatment for gallbladder disease. In HMO, Medicare, and fee-for-service settings, cholecystectomy rates increased 28% to 59% after introduction of laparoscopic cholecystectomy.

OBJECTIVE

To investigate the impact of the introduction of laparoscopic cholecystectomy on cholecystectomy rates and the operative mortality rate in Veterans Affairs (VA) hospitals.

DESIGN

Sequential cross-sectional study.

PATIENTS

All patients who underwent cholecystectomy from 1991 (before introduction of laparoscopic cholecystectomy) to 1995.

SETTING

133 VA hospitals.

OUTCOME MEASURES

Cholecystectomy rates, use of laparoscopic or open cholecystectomy, and operative mortality rate.

RESULTS

The annual number of cholecystectomies in the VA system increased by 10% from 1991 to 1995; the laparoscopic procedure accounted for 25% of the caseload in 1992 and 52% in 1995. Compared with patients having laparoscopic cholecystectomy, those having open cholecystectomy were more likely to be older, be male, and have acute cholecystitis or comorbid illnesses (P < 0.001). The operative mortality rate of open cholecystectomy increased by 46% during this 4-year period (from 2.4% to 3.4%) and was constant for laparoscopic cholecystectomy (about 0.5%). Given the increasing use of the laparoscopic procedure, however, the overall mortality rate of cholecystectomy during surgery decreased by 22% (from 2.4% to 1.8%). Despite increased use of the surgery, the absolute number of deaths decreased by 9%.

CONCLUSIONS

The introduction of laparoscopic cholecystectomy in the VA system was not accompanied by a large increase in cholecystectomy rates, as it was in fee-for-service, Medicare, and HMO systems. Because the rate of operations has changed only slightly, the total number of cholecystectomy-related deaths has decreased.

Postpartum home visits: extending the continuum of care from hospital to home

Crucial maternal, newborn, and family healthcare needs arise during the early postpartum period, providing the opportunity for home care nurses to extend the continuum of care from hospital to home. This study identifies common early postpartum problems discovered on home health visits and describes the related interventions of home health nurses. Correlational analysis revealed that young mothers, first-time mothers, breastfeeding mothers, and single mothers are priority candidates for follow-up home care.

Identification of an interstitial deletion in an adult female with schizophrenia, mental retardation, and dysmorphic features: further support for a putative schizophrenia-susceptibility locus at 5q21-23.1

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Kinematic gait analysis in dogs with hip dysplasia

OBJECTIVE

To define alterations of movement in dogs with hip dysplasia by use of noninvasive, 3-dimensional, computer-assisted kinematic gait analysis.

DESIGN

Kinematic and force plate data were collected at the trot from clinically normal dogs and from dogs with hip dysplasia.

ANIMALS

12 large adult dogs of various breeds with clinical and radiographic evidence of hip dysplasia, and 12 clinically normal adult large dogs of various breeds with body weight similar to that of the dogs with hip dysplasia.

PROCEDURE

Dynamic flexion and extension angles and angular velocities were calculated for the coxofemoral, femorotibial, and tarsal joints. Temporal and distance variables were also computed. Essential Fourier coefficients were determined and used to reconstruct mean dynamic flexion and extension curves for all joints, and to compare differences in movement between dogs with hip dysplasia and clinically normal dogs.

RESULTS

Dogs with hip dysplasia had subtle characteristic changes in dynamic flexion and extension angles and angular velocities of each joint, verified by significant differences in essential Fourier coefficients between the 2 study groups. Stride length was increased and peak vertical force was decreased in dogs with hip dysplasia. Subject velocity, maximal foot velocity, stance duration, stride frequency, and impulse area did not differ between the 2 groups.

CONCLUSIONS

Kinematic gait analysis indicated that hip dysplasia is associated with alterations in movement of the coxofemoral, femorotibial, and tarsal joints. Computer-assisted kinematic gait analysis provided a noninvasive, objective tool with which to evaluate these complex motion alterations.

CLINICAL RELEVANCE

The information obtained may be useful in future evaluations of various modes of treatment for hip dysplasia.

The REC1 gene of Ustilago maydis, which encodes a 3'-->5' exonuclease, couples DNA repair and completion of DNA synthesis to a mitotic checkpoint

Mutation in the REC1 gene of Ustilago maydis results in extreme sensitivity to killing by ultraviolet light. The lethality of the rec1-1 mutant was found to be partially suppressed if irradiated cells were held artificially in G2-phase by addition of a microtubule inhibitor. This mutant was also found to be sensitive to killing when DNA synthesis was inhibited by external means through addition of hydroxyurea or by genetic control in a temperature-sensitive mutant strain defective in DNA synthesis. Flow cytometric analysis of exponentially growing cultures indicated that wild-type cells accumulated in G2 after UV irradiation, while rec1-1 cells appeared to exit from G2 and accumulate in G1/S. Analysis of mRNA levels in synchronized cells indicated that the REC1 gene is periodically expressed with the cell cycle and reaches maximal levels at G1/S. The results are interpreted to mean that a G2-M checkpoint is disabled in the rec1-1 mutant. It is proposed that the REC1 gene product functions in a surveillance system operating during S-phase and G2 to find and repair stretches of DNA with compromised integrity and to communicate with the cell cycle apparatus.

Aortic root complications in Marfan's syndrome: identification of a lower risk group

OBJECTIVES

The purpose of this study was to examine clinical and echocardiographic predictors of outcome in a cohort of patients with Marfan's syndrome.

BACKGROUND

Serial echocardiographic measurements of aortic root dimensions are an important clinical method for monitoring patients with Marfan's syndrome. However, there are few data on the prognostic importance of echocardiographic variables for risk stratification and timing of aortic root replacement.

METHODS

In 89 consecutive patients with Marfan's syndrome (age range 1-54 years) clinical and serial echocardiographic data (n = 62) were evaluated as potential predictors of outcome (mean (range) follow up 4 (< 1-16) years). Aortic sinus diameter and an aortic ratio normalised for age and body surface area were examined using Kaplan-Meier life table and Cox regression analysis, with the end point defined as death or surgery for ascending aortic dissection and events defined as an end point or surgery for ascending aortic aneurysm.

RESULTS

Overall actuarial survival at two and five years was 96% and 92% and event free survival was 85% and 76%, respectively. There were five deaths due to aortic dissection, four patients survived surgery for ascending dissection, and nine underwent root replacement with a composite graft for ascending aneurysm. Those with aortic events were older (35 (12) v 25 (13) years, P = 0.007) and had greater initial aortic root dimensions (47 (14) v 33 (8) mm, P < 0.0001) and ratios (1.6 (0.5) v 1.3 (0.2), P < 0.0001). In the 62 patients with serial echocardiographic follow up, the rate of aortic root dilatation was more rapid in those with events (15 (17) v 0 (3)%/year, P < 0.0001). Utilising a Cox proportional hazards model, the groups with an initial aortic ratio > or = 1.3 or an annual change in aortic ratio > or = 5% had a relative risk of an aortic complication of 2.7 and 4.1, respectively (95% confidence limits 1.5 to 4.8 and 1.8 to 9.3). Only one of 31 patients with an initial aortic ratio of < 1.3 and a rate of change of < 5% had an event (five year event free survival 97%).

CONCLUSIONS

A low risk subgroup of patients with Marfan's syndrome can be identified as those with an aortic ratio < 1.3 and an annual change in aortic ratio of < 5%. These findings are helpful in optimising echocardiographic monitoring and risk stratification of patients with Marfan's syndrome.

Mutation avoidance and DNA repair proficiency in Ustilago maydis are differentially lost with progressive truncation of the REC1 gene product

The REC1 gene of Ustilago maydis has an uninterrupted open reading frame, predicted from the genomic sequence to encode a protein of 522 amino acid residues. Nevertheless, an intron is present, and functional activity of the gene in mitotic cells requires an RNA processing event to remove the intron. This results in a change in reading frame and production of a protein of 463 amino acid residues. The 3'-->5' exonuclease activity of proteins derived from the REC1 genomic open reading frame, the intronless open reading frame, and several mutants was investigated. The mutants included a series of deletions constructed by removing restriction fragments at the 3' end of the cloned REC1 gene and a set of mutant alleles previously isolated in screens for radiation sensitivity. All of these proteins were overproduced in Escherichia coli as N-terminal polyhistidine-tagged fusions that were subsequently purified by immobilized metal affinity chromatography and assayed for 3'-->5' exonuclease activity. The results indicated that elimination of the C-terminal third of the protein did not result in a serious reduction in 3'-->5' exonuclease activity, but deletion into the midsection caused a severe loss of activity. The biological activity of the rec1-1 allele, which encodes a truncated polypeptide with full 3'-->5' exonuclease activity, and the rec1-5 allele, which encodes a more severely truncated polypeptide with no exonuclease activity, was investigated. The two mutants were equally sensitive to the lethal effect of UV light, but the spontaneous mutation rate was elevated 10-fold over the wild-type rate in the rec1-1 mutant and 100-fold in the rec1-5 mutant. The elevated spontaneous mutation rate correlated with the ablation of exonuclease activity, but the radiation sensitivity did not. These results indicate that the C-terminal portion of the Rec1 protein is not essential for exonuclease activity but is crucial in the role of REC1 in DNA damage repair.