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The ligand for the Kit receptor tyrosine kinase is Kit ligand (Kitl; also known as mast cell growth factor, stem cell factor, and Steel factor), which is encoded at the Steel (Sl) locus of mice. Previous studies revealed that Kitl(Sl) mutations have semidominant effects; mild pigmentation defects and macrocytic, hypoplastic anemia occur in heterozygous mice, and more severe pigmentation defects and anemia occur in homozygotes. Lethality also occurs in mice homozygous for severe Kitl(Sl) mutations. We describe the effects of seven new N-ethyl-N-nitrosourea (ENU)-induced Kitl(Sl) mutations and two previously characterized severe Kitl(Sl) mutations on pigmentation, peripheral blood cells, and mouse survival. Mice heterozygous for each of the nine mutations had reduced coat pigmentation and macrocytosis of peripheral blood. In the case of some of these mutations, however, red blood cell (RBC) counts, hemoglobin concentrations, and hematocrits were normal in heterozygotes, even though homozygotes exhibited severely reduced RBC counts and lethality. In homozygous mice, the extent of anemia generally correlates with effects on viability for most Kitl(Sl) mutations; i.e., most mutations that cause lethality also cause a more severe anemia than that of mutations that allow viability. Interestingly, lethality and anemia were not directly correlated in the case of one Kitl(Sl) mutation.

Background: Prices for prescription drugs vary widely in the United States, from the prices charged by retail pharmacies to 50% below average wholesale prices (AWP), depending on the purchaser's bargaining power. At higher drug prices, expenditures for essential preventive interventions, such as those aimed at hypertension and hypercholesterolemia, buy less health for the elderly. The magnitude of this effect, however, is unknown., Methods: Cost-effectiveness analyses of drug interventions, which estimate their health effects and costs, sometimes include analyses of the impact of drug prices. We use results from studies of preventive drugs used by the elderly to calculate the life-years that could be purchased for $1 million of expenditure at the AWP, and at prices 20% and 40% below the AWP. This range reflects the range of prices in the United States today., Results: Drug prices have a substantial effect on the amount of health that can be purchased for $1 million, especially among elderly people with several health conditions. For example, at 40% below the AWP, $1 million spent on statins yields 90 years of life for patients aged 75 to 84 with a history of myocardial infarction. At the AWP, the number of life-years for $1 million drops to 48--a loss of 42 life-years., Conclusions: A Medicare drug benefit program that supports prices at the high end of the current range could yield substantially less health for the elderly, and one that promotes differential pricing could promote unequal access to preventive medications--and thus to health--by Medicare beneficiaries across the country.

Agouti is a paracrine-acting, transient antagonist of melanocortin 1 receptors that specifies the subapical band of yellow on otherwise black hairs of the wild-type coat. To better understand both agouti structure/function and the germline damage caused by chemicals and radiation, an allelic series of 25 recessive, homozygous-viable agouti mutations generated in specific-locus tests were characterized. Visual inspection of fur, augmented by quantifiable chemical analysis of hair melanins, suggested four phenotypic categories (mild, moderate, umbrous-like, severe) for the 18 hypomorphs and a single category for the 7 amorphs (null). Molecular analysis indicated protein-coding alterations in 8 hypomorphs and 6 amorphs, with mild-moderate phenotypes correlating with signal peptide or basic domain mutations, and more devastating phenotypes resulting from C-terminal lesions. Ten hypomorphs and one null demonstrated wild-type coding potential, suggesting that they contain mutations elsewhere in the > or = 125-kb agouti locus that either reduce the level or alter the temporal/spatial distribution of agouti transcripts. Beyond the notable contributions to the field of mouse germ cell mutagenesis, analysis of this allelic series illustrates that complete abrogation of agouti function in vivo occurs most often through protein-coding lesions, whereas partial loss of function occurs slightly more frequently at the level of gene expression control.

The piebald deletion complex is a set of overlapping chromosomal deficiencies surrounding the endothelin receptor B locus collected during the Oak Ridge specific-locus-test mutagenesis screen. These chromosomal deletions represent an important resource for genetic studies to dissect the functional content of a genomic region, and several developmental defects have been associated with mice homozygous for distinct piebald deletion alleles. We have used molecular markers to order the breakpoints for 20 deletion alleles that span a 15.7-18-cM region of distal mouse chromosome 14. Large deletions covering as much as 11 cM have been identified that will be useful for regionally directed mutagenesis screens to reveal recessive mutations that disrupt development. Deletions identified as having breakpoints positioned within previously described critical regions have been used in complementation studies to further define the functional intervals associated with the developmental defects. This has focused our efforts to isolate genes required for newborn respiration and survival, skeletal patterning and morphogenesis, and central nervous system development.

Background: The NHANES I Epidemiologic Follow-Up Study (NHEFS), a longitudinal study of a representative sample of U.S. adults, makes it possible for the first time to develop a simulation model relating hospital admissions to baseline clinical risk factors for the general adult population. The model is presented here and used to project the impact on hospital admissions of changes in smoking behavior and sedentary lifestyle., Methods: Three kinds of projections were calculated for the cohort of adults aged 45 to 74 at baseline: projections of hospital admissions in the absence of the risk factor; projections that reflect a 10-year lag between behavior change and full health benefit; and projections that reflect both lag and incomplete adherence to behavior change. For incomplete adherence we assumed that only 10% of the at-risk population changed their behavior., Results: Tests of the simulation model showed that it agreed with a Cox analysis of the hospital data and accurately projected observed hospital admissions over the study period. The projections showed that eliminating smoking would reduce annual rates of all-cause hospitalization among older adults by 8.9% 20 years after baseline. Eliminating inactivity would reduce them 4.6%. Introducing a lag of 10 years between behavior modification and full benefit delayed the impact on hospitalization rates but the effect at 20 years was the same. When only 10% of the population at risk stopped smoking or became physically active, a percentage that reflects the effectiveness of current interventions, annual hospitalization rates at 20 years fell by 0.9% and 0.5%, respectively., Conclusions: Substantial reductions in hospital admissions can be achieved by interventions to prevent smoking, help smokers quit, or encourage inactive persons to become active. Improving adherence can markedly improve the impact on hospitalizations. The costs of these efforts would be rewarded not only by better health, but by lower expenditures for hospitalization.

This study examined relative hazards for mortality and functional limitations according to poor self-ratings of health using prospective data from the NHANES I Epidemiologic Follow-up Study, a representative sample of US adults aged 25-74 years that has been followed since the First National Health and Nutrition Examination Survey (NHANES I) was conducted in 1971-1975. Follow-up data were taken from death records and from the 1982 and 1992 reinterviews. Respondents (n = 6,913) provided extensive baseline data through physician examinations, laboratory testing, and self-reports of conditions, symptoms, and risk behaviors. Functional limitations were assessed among survivors in 1982 and 1992. Cox regression models accounting for sample design indicated that baseline self-rated health was associated with a significantly reduced hazard of mortality for males but not for females through 1992; adjusted hazards ratios for excellent health as compared with poor health were 0.52 for males (95% confidence interval: 0.36, 0.73) and 0.80 for females (95% confidence interval: 0.51, 1.23). Self-rated health also predicted 1982 and 1992 functional limitation for both men and women and 1992 function net of 1982 function for men only. Self-rated health contributes unique information to epidemiologic studies that is not captured by standard clinical assessments or self-reported histories, but evidence suggests that the effect may be stronger for men than for women.

Objectives: Cost-effectiveness analysts often present cost-effectiveness results by age to help inform decisions about the use of an intervention. Yet it is not known how well studies model the risks and costs associated with age. We reviewed published studies to examine their modeling of age differences., Methods: MEDLINE searches identified all cost-effectiveness analyses published between 1985 and 1997 that included adults 50 years of age and older, were based on data for developed countries, and compared cost-effectiveness ratios for adults of different ages or for initiation of an intervention at different ages; 36 articles met these criteria. They were reviewed to determine the extent to which they incorporated age-specific data. Studies that justified using the same data for all ages were counted as having varied the data element by age., Results: All studies varied life expectancy by age. Most also varied the incidence/prevalence of the target condition and the case fatality rate. Only 36% varied the effectiveness rate of the intervention by age. Costs were usually assumed constant: 42% of studies varied the cost of treating adverse effects and 17% varied the cost of treating the target condition. Whether a data element was varied did not appear to be related to the pattern of cost-effectiveness ratios by age., Conclusions: Many studies have not modeled age differences in sufficient detail to ensure that differences in cost-effectiveness ratios by age are accurate and a sound basis for decisions. As cost-effectiveness analysis becomes more widespread, analysts should strive to incorporate more complete age-specific data.

Dominant-lethal tests [P.D. Sudman, J.C. Rutledge, J.B. Bishop, W.M. Generoso, Bleomycin: female-specific dominant lethal effects in mice, Mutat. Res. 296 (1992) 205-217] had suggested that Bleomycin sulfate (Blenoxane), BLM, might be a female-specific mutagen. While confirming that BLM is indeed a powerful inducer of dominant-lethal mutations in females that fails to induce such mutations in postspermatogonial stages of males, we have shown in a specific-locus test that BLM is, in fact, mutagenic in males. This mutagenicity, however, is restricted to spermatogonia (stem-cell and differentiating stages), for which the specific-locus mutation rate differed significantly (P<0.008) from the historical control rate. In treated groups, dominant mutations, also, originated only in spermatogonia. With regard to mutation frequencies, this germ-cell-stage pattern is different from that for radiation and for any other chemical studied to date, except ethylnitrosourea (ENU). However, the nature of the spermatogonial specific-locus mutations differentiates BLM from ENU as well, because BLM induced primarily (or, perhaps, exclusively) multilocus deletions. Heretofore, no chemical that induced specific-locus mutations in spermatogonia did not also induce specific-locus as well as dominant-lethal mutations in postspermatogonial stages, making the dominant lethal test, up till now, predictive of male mutagenicity in general. The BLM results now demonstrate that there are chemicals that can induce specific-locus mutations in spermatogonia without testing positive in postspermatogonial stages. Thus, BLM, while not female-specific, is unique, (a) in its germ-cell-stage specificity in males, and (b) in inducing a type of mutation (deletions) that is atypical for the responding germ-cell stages (spermatogonia).

The dilute (d), leaden (ln), and ashen (ash) mutations provide a unique model system for studying vesicle transport in mammals. All three mutations produce a lightened coat color because of defects in pigment granule transport. In addition, all three mutations are suppressed by the semidominant dilute-suppressor (dsu), providing genetic evidence that these mutations function in the same or overlapping transport pathways. Previous studies showed that d encodes a major vesicle transport motor, myosin-VA, which is mutated in Griscelli syndrome patients. Here, using positional cloning and bacterial artificial chromosome rescue, we show that ash encodes Rab27a. Rab GTPases represent the largest branch of the p21 Ras superfamily and are recognized as key players in vesicular transport and organelle dynamics in eukaryotic cells. We also show that ash mice have platelet defects resulting in increased bleeding times and a reduction in the number of platelet dense granules. These defects have not been reported for d and ln mice. Collectively, our studies identify Rab27a as a critical gene for organelle-specific protein trafficking in melanocytes and platelets and suggest that Rab27a functions in both MyoVa dependent and independent pathways.

Cost-effectiveness analysis is a method for identifying those medical interventions that are most effective given the resources available. This commentary focuses on the cost effectiveness of screening tests, with particular emphasis on such factors as the frequency and accuracy of the test; the risk of the condition and of adverse effects; the costs of screening, follow-up, and treatment; and the target population. The same test can be much more or less costly per year of life saved, and thus a better or worse use of medical resources, depending on how it is used. Results from cost-effectiveness analyses of a variety of screening interventions important to women (screening for cervical cancer and breast cancer, heart disease, diabetes, and mild thyroid failure) highlight the importance of developing screening protocols wisely so that women will receive the greatest possible benefit from their use.

The human tyrosinase-derived peptide YMDGTMSQV is presented on the surface of human histocompatibility leukocyte antigen (HLA)-A*0201(+) melanomas and has been suggested to be a tumor antigen despite the fact that tyrosinase is also expressed in melanocytes. To gain information about immunoreactivity and self-tolerance to this antigen, we established a model using the murine tyrosinase-derived homologue of this peptide FMDGTMSQV, together with transgenic mice expressing the HLA-A*0201 recombinant molecule AAD. The murine peptide was processed and presented by AAD similarly to its human counterpart. After immunization with recombinant vaccinia virus encoding murine tyrosinase, we detected a robust AAD-restricted cytotoxic T lymphocyte (CTL) response to FMDGTMSQV in AAD transgenic mice in which the entire tyrosinase gene had been deleted by a radiation-induced mutation. A residual response was observed in the AAD(+)tyrosinase(+) mice after activation under certain conditions. At least some of these residual CTLs in AAD(+)tyrosinase(+) mice were of high avidity and induced vitiligo upon adoptive transfer into AAD(+)tyrosinase(+) hosts. Collectively, these data suggest that FMDGTMSQV is naturally processed and presented in vivo, and that this presentation leads to substantial but incomplete self-tolerance. The relevance of this model to an understanding of the human immune response to tyrosinase is discussed.

Unlike other chemicals that have been tested in mammalian germ cells, the type-II topoisomerase inhibitor etoposide exhibits significant mutagenicity in primary spermatocytes. Because this is the cell stage during which meiotic recombination normally occurs, and because topoisomerases play a role in recombination, we studied the effect of etoposide on crossing-over in male mice. Exposure to those meiotic prophase stages (probably early to mid-pachytene) during which specific-locus deletion mutations can be induced resulted in decreased crossing-over in the p-Tyr(c) interval of mouse chromosome 7. Accompanying cytological studies with fluorescent antibodies indicated that while there was no detectable effect on the number of recombination nodules (MLH1 foci), there were marked changes in the stage of appearance and localization of RAD51 and RPA proteins. These temporal and spatial protein patterns suggest the formation of multiple lesions in the DNA after MLH1 has already disappeared from spermatocytes. Since etoposide blocks religation of the cut made by type II topoisomerases, repair of DNA damage may result in rejoining of the original DNA strands, undoing the reciprocal exchange that had already occurred and resulting in reduced crossing-over despite a normal frequency of MLH1 foci. Crossing-over could conceivably be affected differentially in different chromosomal regions. If, however, the predominant action of etoposide is to decrease homologous meiotic recombination, the chemical could be expected to increase nondisjunction, an event associated with human genetic risk. Three periods in spermatogenesis respond to etoposide in different ways. Exposure of (a) late differentiating spermatogonia (and, possibly, preleptotene spermatocytes) results in cell death; (b) early- to mid-pachytene induces specific-locus deletions and crossover reduction; and, (c) late pachytene-through-diakinesis leads to genetically unbalanced conceptuses as a result of clastogenic damage.

A model creates the framework for a cost-effectiveness analysis, allowing decision makers to explore the implications of using an intervention in different ways and under different conditions. To serve its purpose a model must produce accurate predictions and allow for substantial variation in the factors that influence costs and effects. This paper considers three aspects of modelling: validating effectiveness estimates; modelling costs; and the implications of common statistical forms. Validation procedures similar to those for effectiveness estimates are proposed for costs. Modellers need to pay more attention to ensuring that the pathway of events described by a model represents costs as well as it does effects. Modellers can also help improve the epidemiological and clinical research on which cost-effectiveness analyses depend by showing the implications for resource allocation of the statistical forms conventionally used in these fields., (Copyright 1999 John Wiley & Sons, Ltd.)

The juvenile development and fertility-2 (jdf2) locus, also called runty-jerky-sterile (rjs), was originally identified through complementation studies of radiation-induced p-locus mutations. Studies with a series of ethylnitrosourea (ENU)-induced jdf2 alleles later indicated that the pleiotropic effects of these mutations were probably caused by disruption of a single gene. Recent work has demonstrated that the jdf2 phenotype is associated with deletions and point mutations in Herc2, a gene encoding an exceptionally large guanine nucleotide exchange factor protein thought to play a role in vesicular trafficking. Here we describe the molecular characterization of a collection of radiation- and chemically induced jdf2/Herc2 alleles. Ten of the 13 radiation-induced jdf2 alleles we studied are deletions that remove specific portions of the Herc2 coding sequence; DNA rearrangements were also detected in two additional mutations. Our studies also revealed that Herc2 transcripts are rearranged, not expressed, or are present in significantly altered quantities in animals carrying most of the jdf2 mutations we analyzed, including six independent ENU-induced alleles. These data provide new molecular clues regarding the wide range of jdf2 and p phenotypes that are expressed by this collection of recently generated and classical p-region mutations.

Background: The U.S. Public Health Service's Panel on Cost-Effectiveness in Health and Medicine recommends that cost-effectiveness analyses (CEAs) intended to help allocate health resources in the public interest include a reference case analysis, conducted from the perspective of society as a whole. This perspective requires that an analysis measure all health effects and changes in resource use caused by an intervention. VALUE OF SOCIETAL CEAs: Tensions unavoidably arise among the parties to medical decisions--patients, their families and friends, clinicians, and third-party payers. One common approach to handling these tensions is to ignore some of them, to "solve" them by pretending they do not or should not exist. Patients do this when they demand the best care for themselves without regard to the cost to others, payers when they make coverage decisions that shift costs ot others. But by estimating all gains and losses, calculations that reflect the safety, effectiveness, and side effects of an intervention as well as its costs, societal CEAs can help resolve those tensions and provide the basis for decisions that are fair to all parties, an agenda for negotiating such decisions, and information essential for designing compensation and incentives to support them. MAKING BETTER USE OF SOCIETAL CEAs: Use of the societal perspective asks that all parties be aware of and consider the interests of others. Some process or procedure needs to be developed for presenting CEA information to the parties most likely to be affected by decisions, soliciting their views, and negotiating an acceptable decision. This process could be used by government decision makers or by managed care organizations, professional societies, or payers.

Background: Previous analyses have found autologous transfusion to be very expensive but have not considered avoidance of postoperative bacterial infections as one of its benefits., Study Design and Methods: A cost-utility analysis using a Markov cohort simulation model compared autologous blood transfusion to allogeneic transfusion in a hypothetical cohort of patients undergoing elective total hip replacement with respect to discounted quality-adjusted life years (QALYs) and health-care system costs., Results: Assuming a base case rate of serious infection of 3.7 percent, a relative risk of infection of 1.85, and additional costs of $12,980 per infection, autologous transfusion has a cost-effectiveness of $2,470 per QALY. If the relative risk of bacterial infection following allogeneic transfusion exceeds 1.1, the cost-effectiveness of autologous transfusion is less than $50,000 per QALY and if the relative risk exceeds 2.4, autologous transfusion is dominant, resulting in both lower costs and greater QALYs. If there were no increased risk of transfusion, the cost-effectiveness of autologous transfusion would be $3,400,000 per QALY., Conclusions: If there is only a modest increase in the risk of bacterial infection following allogeneic transfusion, autologous transfusion would result in improved outcomes at a cost of less than $50,000 per QALY. Autologous transfusion would be dominant above a relative risk of infection that is within the range of values observed in randomized controlled trials. However, if there is no increased risk of bacterial infection, autologous transfusion would be a very expensive strategy. Until more definitive data are available on the magnitude and costs of this risk, we advise against prematurely closing the debate about the cost-effectiveness of autologous transfusion.

An earlier analysis showed that a significant percentage of spontaneous specific-locus mutations in mice are recovered as mosaics and that the spontaneous mutation rate per cell cycle is probably higher for those mutations that produce mosaics than for those that produce whole-body mutants. The finding that the average germline composition of the mosaics was approximately 50% supported the suggestion that single-strand DNA alterations during the perigametic interval constitute the major source of spontaneous mosaics. Here, alternative origins of 50% germline mosaicism are examined. Supporting the earlier hypothesis is the finding that spontaneous mutations that are recovered as clusters constitute a different array of types from those giving rise to singletons, and the evidence from interspecies comparisons that a unique component of the life cycle, probably meiosis, makes a major contribution to spontaneous mutations. Biological factors associated with the perigametic interval were examined in an effort to suggest explanations for the observations that 1) the spontaneous mutation rate in that interval is high relative to that characterizing any mitotic cell cycle, 2) the types of mutations appear to be different from those arising during mitotic divisions, and 3) the spontaneous mutation rate for males is higher than that for females. It is concluded that the higher yield from the perigametic interval is consistent with what is known about methylation status in development of both sexes and with repair capacity in the male germline. For both parameters, differences between the sexes during their respective perigametic intervals may be at least partly responsible for the fact that the spontaneous mutation rate of mammalian females is lower than that of males., (Copyright 1999 Wiley-Liss, Inc.)

The cancer chemotherapy agent, and topoisomerase-II inhibitor, etoposide (VP-16) produced both recessive mutations at specific loci and dominants at other loci with peak frequencies in primary spermatocytes, a cell type in which the topo-II gene has been shown to be activated. Etoposide thus differs from all other chemicals whose germ-cell-stage specificity has been analyzed. No effects of etoposide exposure of spermatogonial stem cells ( approximately 15, 000 offspring scored) were detectable by either mutagenicity or productivity endpoints. The significant mutagenic response that followed exposure of poststem-cell stages ( approximately 25,000 offspring scored) showed a clear peak, with three of four specific-locus mutants, and three of four dominant mutants conceived during weeks 4 or 5 (days 22-35) post-injection, a period that also encompassed the dominant-lethal peak. For this period, the induced specific-locus rate (with 95% confidence limits) at a weighted-average exposure of 75.1 mg etop/kg was 59.5 (14.6, 170. 9)x10-6/locus. At least 3 of the 4 specific-locus mutations were deletions, paralleling findings with etoposide or analogs in other test systems where a recombinational origin of the deletions has been suggested. Because, unlike other chemicals that induce deletions in male germ cells, etoposide is effective in stages normally associated with recombinational events, it will be of interest to determine whether this chemical can affect meiotic recombination., (Copyright 1998 Elsevier Science B.V. All rights reserved.)

We used an RT-PCR-based sequencing approach to identify the mutations responsible for 17 viable dilute alleles, a mouse-coat-color locus encoding unconventional myosin-VA. Ten of the mutations mapped to the MyoVA tail and are reported here. These mutations represent the first extensive collection of tail mutations reported for any unconventional mammalian myosin. They identify sequences important for tail function and identify domains potentially involved in cargo binding and/or proper folding of the MyoVA tail. Our results also provide support for the notion that different myosin tail isoforms produced by alternative splicing encode important cell-type-specific functions.

Objectives: A model that relates clinical risk factors to subsequent mortality was used to simulate the impact of smoking cessation., Methods: Survivor functions derived from multivariate hazard regressions fitted to data from the first National Health and Nutrition Examination Survey (NHANES I) Epidemiologic Followup Study, a longitudinal survey of a representative sample of US adults, were used to project deaths from all causes., Results: Validation tests showed that the hazard regressions agreed with the risk relationships reported by others, that projected deaths for baseline risk factors closely matched observed mortality, and that the projections attributed deaths to the appropriate levels of important risk factors. Projections of the impact of smoking cessation showed that the number of cumulative deaths would be 15% lower after 5 years and 11% lower after 20 years., Conclusions: The model produced realistic projections of the effects of risk factor modification on subsequent mortality in adults, Comparison of the projections for smoking cessation with estimates of the risk attributable to smoking published by the Centers for Disease Control and Prevention suggests that cessation could capture most of the benefit possible from eliminating smoking.

The mouse dilute (d) locus encodes unconventional myosin-VA (MyoVA). Mice carrying null alleles of dilute have a lightened coat color and die from a neurological disorder resembling ataxia and opisthotonus within three weeks of birth. Immunological and ultrastructural studies suggest that MyoVA is involved in the transport of melanosomes in melanocytes and smooth endoplasmic reticulum in cerebellar Purkinje cells. In studies described here, we have used an RT-PCR-based sequencing approach to identify the mutations responsible for 17 viable dilute alleles that vary in their effects on coat color and the nervous system. Seven of these mutations mapped to the MyoVA motor domain and are reported here. Crystallographic modeling and mutant expression studies were used to predict how these mutations might affect motor domain function and to attempt to correlate these effects with the mutant phenotype.

In an attempt to provide a systematic assessment of the frequency and nature of mutations induced in successive stages of spermato- and spermiogenesis, X-irradiated male mice were re-mated at weekly intervals, and large samples of progeny, observed from birth onward, were scored and genetically tested for recessive mutations at seven specific loci and for externally recognizable dominant mutations. Productivity findings provided a rough measure of induced dominant-lethal frequencies. A qualitative assessment of specific-locus mutations (which include deletions and other rearrangements) was made on the basis of homozygosity test results, as well as from information derived from more recent complementation studies and molecular analyses. Both recessive and dominant visibles revealed clear distinctions between spermatogonia and postspermatogonial stages. In addition, differences for both of these endpoints, as well as for presumed dominant lethals, were found among various postspermatogonial stages. It may be concluded that radiation produces its maximum rates of genetic damage in germ-cell stages ranging from midpachytene spermatocytes through early spermatids, a pattern unlike any of those that have been defined for chemicals; further, the frequency peaks for radiation are lower and broader. The difference between post-stem-cell stages overall and stem-cell spermatogonia was smaller than is generally found with chemicals, not only with respect to the frequency but also the nature of mutations.

Objectives: This study examines the influence of risk factors such as cigarette smoking, blood pressure, serum cholesterol, or chronic illness on frequency of hospital admission in a population-based sample., Methods: Data from the National Health and Nutrition Examination Survey I Epidemiologic Followup Study for 6,461 adults aged 45 years and older were used to assess the influence of risk factors measured by interview, physical examination, and laboratory tests on frequency of hospital admission over a 12- to 16-year follow-up period. Cox proportional hazard regressions were estimated separately for men and women and for ages 45 to 64 years and 65 years and older. SUDAAN software was used to correct for clustering, stratification, unequal weighting, and multiple observations per respondent., Results: Risk of hospitalization was higher for current but not former smokers (relative risk [RR] = 1.17-1.34 for different age-sex groups; P < 0.01), higher blood pressure (RR = 1.25-1.28 for ages 45-64; RR = 1.07-1.15 for ages 65 and older; P < 0.01), and lower serum albumin (RR = 1.08-1.14; P < 0.01). Diabetes, lung conditions, heart attack, and ulcer each were associated with higher risk in at least three of the four age-sex groups, as was arthritis among the middle-aged (45-64 years). Serum cholesterol was not associated with hospitalization., Conclusions: Chronic conditions with high morbidity as well as many factors associated with mortality are associated with a higher frequency of hospitalization.

Bone morphogenetic proteins (BMPs) are secreted signaling molecules that control important developmental events in many different organisms. Previous studies have shown that BMPs are expressed at the earliest stages of skeletal development, and are required for formation of specific skeletal features, strongly suggesting that they are endogenous signals used to control formation of skeletal tissue. Despite the importance of BMP signaling in normal development, very little is known about the mechanisms that control the synthesis and distribution of BMP signals in vertebrates. Here, we identify a large array of cis-acting control sequences that lay out expression of the mouse Bmp5 gene in specific skeletal structures and soft tissues. Some of these elements show striking specificity for particular anatomical features within the skeleton, rather than for cartilage and bone in general. These data suggest that the vertebrate skeleton is built from the sum of many independent domains of BMP expression, each of which may be controlled by separate regulatory elements driving expression at specific anatomical locations. Surprisingly, some of the regulatory sequences in the Bmp5 gene map over 270 kb from the Bmp5 promoter, making them among the most distant elements yet identified in studies of eukaryotic gene expression.

The piebald locus on mouse chromosome 14 encodes the endothelin-B receptor (EDNRB), a G protein-coupled, seven-transmembrane domain protein, which is required for neural crest-derived melanocyte and enteric neuron development. A spontaneous null allele of Ednrb results in homozygous mice that are predominantly white and die as juveniles from megacolon. To identify the important domains for EDNRB function, four recessive juvenile lethal alleles created by either radiation or chemical mutagens (Ednrb27Pub, Ednrb17FrS, Ednrb1Chlc, and Ednrb3Chlo) were examined at the molecular level. Ednrb27Pub mice harbor a mutation at a critical proline residue in the fifth transmembrane domain of the EDNRB protein. A gross genomic alteration within the Ednrb gene in Ednrb3Chlo results in the production of aberrantly sized transcripts and no authentic Ednrb mRNA. Ednrb17FrS mice exhibited a decreased level of Ednrb mRNA, supporting previous observations that the degree of spotting in piebald mice is dependent on the amount of EDNRB expressed. Finally, no molecular defect was detected in Ednrb1Chlc mice, which produce normal levels of Ednrb mRNA in adult brain, suggesting that the mutation affects important regulatory elements that mediate the expression of the gene during development.

Objectives: This report compares hospitalization data from the NHANES I Epidemiologic Followup Study (NHEFS) with data from the National Hospital Discharge Survey (NHDS), the benchmark for hospitalization in the United States, for men and women 35 years and older for the period 1971-87. The comparison is intended to help analysts evaluate the validity and generality of analyses based on the NHEFS., Methods: Hospital stays per 1,000 population and average lengths of stay are compared year by year for each age-sex group and for the entire period. Regression analyses test for differences between the two surveys by age and sex, and for differences in trends over time and the effect of the Medicare program's prospective hospital payment system., Results: Hospital stays per 1,000 population were lower in NHEFS than in NHDS in all age-sex groups at the beginning of the period, but the differences had almost disappeared by 1987. Lengths of stay, although somewhat longer in NHEFS, matched NHDS more closely. Differentials by age and sex were similar in the two surveys for both hospital stays per 1,000 population and length of hospital stay. With its extensive information on baseline risk factors, the NHEFS offers a unique opportunity to study determinants of hospitalization in a representative sample of U.S. adults. The evaluation presented here suggests two points for researchers who want to use the NHEFS. First, including age as a control should largely correct for differences in age distribution between NHEFS and NHDS. Second, a time trend should also be included to capture the effects of several factors that caused the count of stays to be low in the early years of NHEFS followup.

Due to the rapid advances that have been made in molecular and genetic technology during the past decade, the genes associated with a large number of human hereditary diseases have been isolated and analyzed in detail. These cloned genes provide new tools for research geared toward a better understanding of normal human development, and also of the many ways that basic, essential morphologic pathways can be disturbed. Chromosomal rearrangements, especially deletions and translocations, have been especially beneficial in the mapping and isolation of human disease genes because of their visibility on both the cytogenetic and molecular levels. However, these useful types of mutations occur with low frequency in the human population. Chromosomal rearrangements can be induced relatively easily in mice, and several large, independent collections of translocation and deletion mutants have been generated in the course of risk-assessment and mutagenesis studies over the past several decades. Combined with new molecular technologies, these collections of mutant animals provide a means of gaining ready access to genes associated with developmental defects including craniofacial abnormalities, hydrocephaly, skeletal deformities, and complex neurologic disorders. As an illustration of this approach, we briefly review our progress in the study of three mutations associated with defects in palate development, juvenile growth, fitness and sterility, and neurologic development in mice, respectively.

This article reports the recommendations of the Panel on Cost Effectiveness in Health and Medicine, sponsored by the US Public Health Service, on standardised methods for conducting cost-effectiveness analyses. Although not expressly directed at analyses of pharmaceutical agents, the Panel's recommendations are relevant to pharmacoeconomic studies. The Panel outlines a 'Reference Case' set of methodological practices to improve quality and comparability of analyses. Designed for studies that inform resource-allocation decisions, the Reference Case includes recommendations for study framing and scope, components of the numerator and denominator of cost-effectiveness ratios, discounting, handling uncertainty and reporting. The Reference Case analysis is conducted from the societal perspective, and includes all effects of interventions on resource use and health. Resource use includes 'time' resources, such as for caregiving or undergoing an intervention. The quality-adjusted life-year (QALY) is the common measure of health effect across Reference Case studies. Although the Panel does not endorse a measure for obtaining quality-of-life weights, several recommendations address the QALY. The Panel recommends a 3% discount rate for costs and health effects. Pharmacoeconomic studies have burgeoned in recent years. The Reference Case analysis will improve study quality and usability, and permit comparison of pharmaceuticals with other health interventions.

Over 40 years of mutagenesis experiments using the mouse specific-locus test have produced a large number of induced germline mutations at seven loci, among them the short ear locus. We have previously shown that the short ear locus encodes bone morphogenetic protein 5 (BMP5), a member of a large family of secreted signaling molecules that play key roles in axis formation, tissue differentiation, mesenchymalepithelial interactions, and skeletal development. Here we examine 24 chemical- and radiation-induced mutations at the short ear locus. Sequence changes in the Bmp5 open reading frame confirm the importance of cysteine residues in the function of TGF beta superfamily members. The spectrum of N-ethyl-N-nitrosourea-induced mutations also provides new information about the basepair, sequence context, and strand specificity of germline mutations in mammals.

The mouse microphthalmia (mi) locus encodes a basic helix-loop-helix-leucine zipper (bHLH-Zip) transcription factor called MITF (microphthalmia transcription factor). Mutations at mi affect the development of several different cell types, including melanocytes, mast cells, osteoclasts and pigmented epithelial cells of the eye. Here we describe the phenotypic and molecular characterization of the semidominant Microphthalmia(brwnish) (Mi(b)) mutation. We show that this mutation primarily affects melanocytes and produces retinal degeneration. The mutation is a G to A transition leading to a Gly244Glu substitution in helix 2 of the HLH dimerization domain. This location is surprising since other semidominant mi mutations characterized to date have been shown to affect DNA binding or transcriptional activation domains of MITF and act as dominant negatives, while mutations that affect MITF dimerization are inherited recessively. Gel retardation assays showed that while the mutant MITF(Mi-b) protein retains its dimerization potential, it is defective in its ability to bind DNA. Computer modeling suggested that the Gly244Glu mutation might disrupt DNA binding by interfering with productive docking of the protein dimer onto DNA. The Mi(b) mutation therefore appears to dissociate a DNA recognition function of the HLH domain from its role in protein dimerization.

The specific-locus test (SLT) detects new mutants among mice heterozygous for seven recessive visible markers. Spontaneous mutations can be manifested not only as singleton whole-body mutants in controls (for which we report new data), but as mosaics-either visible (manifesting mottled coat color) in the scored generation (G2) or masked, among the wild-type parental generation (G1). Masked G1 mosaics reveal themselves by producing clusters of whole-body mutants in G2. We provide evidence that most, if not all, mosaics detected in the SLT (both radiation and control progenies) result from a single-strand spontaneous mutation subsequent to the last premeiotic mitosis and before the first postmeiotic one of a parental genome-the "perigametic interval." Such events in the genomes of the G1 and Gzero results, respectively, in visible and masked 50:50 mosaics. Per cell cycle, the spontaneous mutation rate in the perigametic interval is much higher than that in pregamete mitotic divisions. A clearly different locus spectrum further supports the hypothesis of different origin, and casts further doubt on the validity of the doubling-dose risk-estimation method. Because mosaics cannot have arisen in mitotic germ cells, and are not induced by radiation exposure in the perigametic interval, they should not be included in calculations of radiation-induced germ-line mutation rates. For per-generation calculations, inclusion of mosaics yields a spontaneous frequency 1.7 times that calculated from singletons alone for mutations contributed by males; including both sexes, the multiple is 2.2.

Specific-locus studies have shown chlorambucil (CHL) and bleomycin (BLE) to be mutagenic in mouse oocytes, almost doubling the number of chemicals previously known to induce mutations in females. The overall CHL-induced mutation rate in oocytes is, however, one order of magnitude below that for male meiotic and postmeiotic stages, and only 1/50 that for early spermatids. For BLE, no specific-locus data for males are available for comparison, but the chemical had earlier been found negative for dominant-lethal induction in males. Both BLE and CHL were significantly mutagenic only in mature and maturing oocytes. In keeping with an earlier report, BLE produced a high incidence of dominant lethals in these stages. CHL failed to induce dominant lethals, indicating that for mature and maturing oocytes, in contrast with results for males, sensitivity to dominant-lethal mutations is not a prerequisite for induction of specific-locus mutations. Exposure of immature oocytes to either BLE or CHL produced neither dominant lethals nor significant induction of specific-locus mutations; however, CHL gave evidence of killing immature oocytes. By contrast, BLE, which has been considered a radiomimetic chemical, does not appear to kill immature oocytes and thus differs markedly from radiation exposures equivalent for dominant-lethal induction. Therefore, the failure to recover specific-locus mutations cannot be ascribed to cell selection resulting from oocyte killing, as has sometimes been done for radiation. Adding results on the nature of the CHL- and BLE-induced mutations to prior information, the estimated minimum proportion of large DNA lesions induced in oocytes by chemicals becomes 35.3%, significantly different from the corresponding figure (approximately 70%) for radiations. For chemical treatments, the oocyte proportion is highly significantly above the 3.6% induced in spermatogonia, but only on the borderline of statistically significant difference from that induced in postspermatogonial stages.

Objective: To develop consensus-based recommendations for the conduct of cost-effectiveness analysis (CEA). This article, the second in a 3-part series, describes the basis for recommendations constituting the reference case analysis, the set of practices developed to guide CEAs that inform societal resource allocation decisions, and the content of these recommendations., Participants: The Panel on Cost-Effectiveness in Health and Medicine, a nonfederal panel with expertise in CEA, clinical medicine, ethics, and health outcomes measurement, was convened by the US Public Health Service (PHS)., Evidence: The panel reviewed the theoretical foundations of CEA, current practices, and alternative methods used in analyses. Recommendations were developed on the basis of theory where possible, but tempered by ethical and pragmatic considerations, as well as the needs of users., Consensus Process: The panel developed recommendations through 2 1/2 years of discussions. Comments on preliminary drafts prepared by panel working groups were solicited from federal government methodologists, health agency officials, and academic methodologists., Conclusions: The panel's methodological recommendations address (1) components belonging in the numerator and denominator of a cost-effectiveness (C/E) ratio; (2) measuring resource use in the numerator of a C/E ratio; (3) valuing health consequences in the denominator of a C/E ratio; (4) estimating effectiveness of interventions; (5) incorporating time preference and discounting; and (6) handling uncertainty. Recommendations are subject to the ¿rule of reason,¿ balancing the burden engendered by a practice with its importance to a study. If researchers follow a standard set of methods in CEA, the quality and comparability of studies, and their ultimate utility, can be much improved.

Homozygous staggerer (sg) mice show a characteristic severe cerebellar ataxia due to a cell-autonomous defect in the development of Purkinje cells. These cells show immature morphology, synaptic arrangement, biochemical properties and gene expression, and are reduced in numbers. In addition, sg heterozygotes show accelerated dendritic atrophy and cell loss, suggesting that sg has a role in mature Purkinje cells. Effects of this mutation on cerebellar development have been studied for 25 years, but its molecular basis has remained unknown. We have genetically mapped staggerer to an interval of 160 kilobases on mouse chromosome 9 which was found to contain the gene encoding RORalpha, a member of the nuclear hormone-receptor superfamily. Staggerer mice were found to carry a deletion within the RORalpha gene that prevents translation of the ligand-binding homology domain. We propose a model based on these results, in which RORalpha interacts with the thyroid hormone signalling pathway to induce Purkinje-cell maturation.

Thirty-six radiation- or chemically induced homozygous-lethal mutations at the p locus in mouse chromosome 7 have been analyzed at 17 loci defined by molecular probes to determine the types of lesions, numbers of p-region markers deleted or rearranged, regions of overlap of deletion mutations, and genetic distances between loci. A linear deletion map of the [Myod1, Ldh3]-[Snrpn, Znf127] region has been constructed from the molecular analyses of the p-locus deletions. The utility of these deletions as tools for the isolation and characterization of the genes specifying the neurological, reproductive, and developmental phenotypes genetically mapped to this region will grow as more detailed molecular analyses continue.

The mouse represents an excellent model system for the study of genetic deafness in humans. Many mouse deafness mutants have been identified and the anatomy of the mouse and human ear is similar. Here we report the use of a positional cloning approach to identify the gene encoded by the mouse recessive deafness mutation, Snell's waltzer (sv). We show that sv encodes an unconventional myosin heavy chain, myosin VI, which is expressed within the sensory hair cells of the inner ear, and appears to be required for maintaining their structural integrity. The requirement for myosin VI in hearing makes this gene an excellent candidate for a human deafness disorder.

The homozygous and heterozygous phenotypes are described and characterized for 45 new pink-eyed dilution (p) locus mutations, most of them radiation-induced, that affect survival at various stages of mouse development. Cytogenetically detectable aberrations were found in three of the new p mutations (large deletion, inversion, translocation), with band 7C involved in each case. The complementation map developed from the study of 810 types of compound heterozygotes identifies five functional units: jls and jlm (two distinct juvenile-fitness functions, the latter associated with neuromuscular defects), pl-1 and pl-2 (associated with early-postimplantation and preimplantation death, respectively), and nl [neonatal lethality associated with cleft palate (the frequency of rare "escapers" from this defect varied with the genotype)]. Orientation of these units relative to genetic markers is as follows: centromere, Gas-2, pl-1, jls, jlm p, nl (equatable to cp 1 = Gabrb3); pl-2 probably resides in the c-deletion complex. pl-1 does not mask preimplantation lethals between Gas2 and p; and no genes affecting survival are located between p and cp1. The alleles specifying mottling or darker pigment (generically, pm and px, respectively) probably do not represent deletions of p-coding sequences but could be small rearrangements involving proximal regulatory elements.

In addition to its function in the nervous system, gamma-aminobutyric acid (GABA) has been implicated in mouse craniofacial development by the results of both teratological, and genetic studies. We previously reported that disruption of the cleft palate 1 (cp1) locus, closely linked to the pink-eyed dilution (p) locus on mouse chromosome 7, causes a 95% penetrant, recessive, neonatally-lethal cleft palate (CP) in mice homozygous for the p(4THO-II) deletion. We proposed that the beta 3 subunit gene (Gabrb3) of the GABAA receptor might be a candidate for cp1 (ref. 4); our earlier studies had localized cp1 to an interval beginning distal to the gene for the GABAA receptor alpha 5 subunit (Gabra5) and ending within the Gabrb3 coding region. To test the hypothesis that deletion of Gabrb3, and not another gene in the interval, causes CP, we performed an experiment to rescue the CP phenotype by introducing a Gabrb3 transgene into p(4THO-II) homozygotes. We now show that such transgenic mice are phenotypically normal, indicating that Gabrb3 is indeed the cp1 locus.

Over a period of many years, germ-cell mutagenesis experiments using the mouse specific-locus test have generated numerous radiation- and chemical-induced alleles of the brown (b; Tyrp 1) locus in mouse chromosome 4. We describe here the origin, maintenance and initial molecular characterization of 28 b mutations that are prenatally lethal when homozygous. Each of these mutations is deleted for Tyrp 1 sequences, and each of 25 mutations tested further is deleted for at least one other locus defined by molecular clones previously found to be closely linked to b by interspecific backcross analysis. A panel of DNAs from mice carrying a lethal b mutation and a Mus spretus chromosome 4 was used in the fine structure mapping of these molecularly defined loci. The deletional nature of each of these prenatally lethal mutations is consistent with the hypothesis that the null phenotype at b has an effect only on the quality (color) of eumelanin produced in melanocytes. The resulting deletion map provides a framework on which to build future molecular-genetic and biological analyses of this region of mouse chromosome 4.

Lethal yellow (Ay) is a mutation at the mouse agouti locus in chromosome 2 that causes a number of dominant pleiotropic effects, including a completely yellow coat color, obesity, an insulin-resistant type II diabetic condition, and an increased propensity to develop a variety of spontaneous and induced tumors. Additionally, homozygosity for Ay results in preimplantation lethality, which terminates development by the blastocyst stage. The Ay mutation is the result of a 170-kb deletion that removes all but the promoter and noncoding first exon of another gene called Raly, which lies in the same transcriptional orientation as agouti and maps 280 kb proximal to the 3' end of the agouti gene. We present a model for the structure of the Ay allele that can explain the dominant pleiotropic effects associated with this mutation, as well as the recessive lethality, which is unrelated to the agouti gene.

Three genes (Gabrg3, Gabra5, and Gabrb3) encoding the gamma 3, alpha 5, and beta 3 subunits of the type A gamma-aminobutyric acid receptor, respectively, are known to map near the pink-eyed dilution (p) locus in mouse chromosome 7. This region shares homology with a segment of human chromosome 15 that is implicated in Angelman syndrome, an inherited neurobehavioral disorder. By mapping Gabrg3 on a panel of p-locus deletions, we have determined that the order of genes within this cluster is centromere-p(D15S12h)-Gabrg3-Gabra5-Gabrb3-telom ere. Like Gabrb3, neither the Gabra5 nor Gabrg3 gene is functionally imprinted in adult mouse brain. Mice deleted for all three subunits die at birth with a cleft palate, although there are rare survivors (approximately 5%) that do not have a cleft palate but do exhibit a neurological abnormality characterized by tremor, jerky gait, and runtiness. We have previously suggested that deficiency of the beta 3 subunit may be responsible for the clefting defect. Most notably, however, in this report we describe mice carrying two overlapping, complementing p deletions that fail to express the gamma 3 transcript, as well as mice from another line that express neither the gamma 3 nor alpha 5 transcripts. Surprisingly, mice from both of these lines are phenotypically normal and do not exhibit any of the neurological symptoms characteristic of the rare survivors that are deleted for all three (gamma 3, alpha 5, and beta 3) subunits. These mice therefore provide a whole-organism type A gamma-aminobutyric-acid receptor background that is devoid of any receptor subtypes that normally contain the gamma 3 and/or alpha 5 subunits. The absence of an overt neurological phenotype in mice lacking the gamma 3 and/or alpha 5 subunits also suggests that mutations in these genes are unlikely to provide useful animal models for Angelman syndrome in humans.

Highlights are presented on (1) the role mouse germ-cell mutagenesis has played in assessing the genetic harm from radiations and chemicals, and (2) the contributions to the field of modern biology that are being made by the products of this research--the propagated mutations. Among the numerous findings in radiation mutagenesis were the humped dose-effect curve for spermatogonial stem cells, the major differences between the sexes and between germ-cell stages of each sex in both yield and nature of mutations, the dose-rate effect, which provided the first evidence for repair of mutational (or premutational) damage, the augmenting effect of certain regimes of dose fractionation, and many others. Chemical mutagenesis studies that followed revealed at least three patterns of mutation yield and demonstrated that germ-cell stage--much more than the nature of the chemical--governs the nature of the DNA lesions induced. Two "supermutagens," one for intragenic mutations and one for deletions and other rearrangements, have become very useful in the manufacture of mutations for specific purposes. The mutations propagated from radiation- and chemical-mutagenesis experiments are providing prime resources for basic studies in genome organization, gene structure, and function. DNA lesions that involve specific loci have made possible increasingly detailed characterization of extensive deletion complexes that facilitate high-intensity physical and functional mapping within them. Numerous loci associated with interesting developmental anomalies have been identified and have become accessible to positional cloning. Several of the genes accessed with the aid of induced mutations (deletions, other rearrangements, and point mutations) are furnishing prime reagents for elucidating human disease conditions.

piebald (s) is a recessive mutation that affects the development of two cell types of neural crest origin: the melanocytes, responsible for pigment synthesis in the skin, and enteric ganglia, which innervate the lower bowel. As a result, mice carrying piebald mutations exhibit white spotting in the coat and aganglionic megacolon. Previously the gene had been localized to the distal half of mouse chromosome 14. To determine its precise location relative to molecular markers, an intersubspecific backcross was generated. Two anchor loci of chromosome 14, slaty and hypogonadal, in addition to simple sequence length repeat markers, were used to localize s to a 2-cM interval defined by the markers D14Mit38 and D14Mit42. The molecular markers were also used to characterize nine induced s alleles. Three of these mutations exhibited no deletions or rearrangements of the flanking markers, whereas the other six had two or more of these markers deleted. The extent of the deletions was found to be consistent with the severity of the homozygous phenotype. The location of deletion breakpoints in the induced alleles, coupled with the recombination breakpoints in the backcross progeny, provide useful molecular landmarks to define the location of the piebald gene.