Somatic activation of the K-ras oncogene causes early onset lung cancer in mice

About 30% of human tumours carry ras gene mutations. Of the three genes in this family (composed of K-ras, N-ras and H-ras), K-ras is the most frequently mutated member in human tumours, including adenocarcinomas of the pancreas ( approximately 70-90% incidence), colon ( approximately 50%) and lung ( approximately 25-50%). To construct mouse tumour models involving K-ras, we used a new gene targeting procedure to create mouse strains carrying oncogenic alleles of K-ras that can be activated only on a spontaneous recombination event in the whole animal. Here we show that mice carrying these mutations were highly predisposed to a range of tumour types, predominantly early onset lung cancer. This model was further characterized by examining the effects of germline mutations in the tumour suppressor gene p53, which is known to be mutated along with K-ras in human tumours. This approach has several advantages over traditional transgenic strategies, including that it more closely recapitulates spontaneous oncogene activation as seen in human cancers.

The natural history of hepatitis C virus infection: host, viral, and environmental factors

CONTEXT

Hepatitis C virus (HCV) infection may resolve (viral clearance), persist without complications, or cause end-stage liver disease (ESLD). The frequency and determinants of these outcomes are poorly understood.

OBJECTIVE

To assess the incidence and determinants of viral clearance and ESLD among persons who acquired HCV infection from injection drug use.

DESIGN AND SETTING

Community-based prospective cohort study with enrollment in 1988-1989 and a median follow-up of 8.8 years.

SUBJECTS

A total of 1667 persons aged 17 years or older with a history of injection drug use and an HCV antibody-positive test result during follow-up.

MAIN OUTCOME MEASURES

Viral clearance was assessed in a subset of 919 patients and defined as failure to detect HCV RNA in at least 2 consecutive samples collected 5 or more months apart. End-stage liver disease was assessed at semiannual visits and by review of medical records and death certificates and defined by the presence of ascites, esophageal varices, or hepatic encephalopathy, or when ESLD was stated as a cause of death.

RESULTS

Viral clearance was observed in 90 persons who were compared with 722 with persistent viremia, while the viremia of 107 was not resolved. Viral clearance occurred more often in nonblacks (adjusted odds ratio [OR], 5.15; 95% confidence interval [CI], 2.60-10.17) and those not infected with human immunodeficiency virus (HIV) (adjusted OR, 2.19; 95% CI, 1.26-3.47). Forty cases of ESLD were observed throughout follow-up (incidence, 3.1 per 1000 person-years). In a multivariate model, risk of ESLD was higher for persons aged 38 years or older at enrollment (adjusted relative incidence, 3.67; 95% CI, 1.96-6.88) and who reported ingestion of more than 260 g of alcohol per week (adjusted relative incidence, 3.60; 95% CI, 1.73-7.52). Of 210 patients without ESLD randomly selected for biopsy, only 2 had cirrhosis.

CONCLUSIONS

Our results indicate that although HCV infection can be self-limited or associated with ESLD, the majority of adults have persistent viremia without clinically demonstrable liver disease. Further research is needed to explain the less frequent clearance of HCV infection among black persons and to improve utilization of treatment for those infected in the context of injection drug use. JAMA. 2000;284:450-456

Relaxation of imprinted genes in human cancer

Genomic imprinting, or parental allele-specific expression of genes, has been demonstrated at the molecular level in insects and mice but not in man. Imprinting as a potential mechanism of human disease is suggested by paternal uniparental disomy of 11p15 in Beckwith-Wiedemann syndrome and by maternal uniparental disomy of 15q11-12 in Prader-Willi syndrome. Beckwith-Wiedemann syndrome is characterized by multiorgan overgrowth and predisposition to embryonal tumours such as Wilms' tumour of the kidney. A loss of heterozygosity of 11p15 is also frequently found in a wide variety of tumours, including Wilms' tumour and lung, bladder, ovarian, liver and breast cancers; 11p15 also directly suppresses tumour growth in vitro. Two genes in this band, H19 and insulin-like growth factor-II (IGF2) undergo reciprocal imprinting in the mouse, with maternal expression of H19 (ref. 13) and paternal expression of IGF2 (ref. 14). Here we find that both of these genes show monoallelic expression in human tissues and, as in mouse, H19 is expressed from the maternal allele and IGF2 from the paternal allele. In contrast, 69% of Wilms' tumours not undergoing loss of heterozygosity at 11p showed biallelic expression of one or both genes, suggesting that relaxation or loss of imprinting could represent a new epigenetic mutational mechanism in carcinogenesis.

Predictive ability of a predischarge hour-specific serum bilirubin for subsequent significant hyperbilirubinemia in healthy term and near-term newborns

OBJECTIVE

To assess the predictive ability of a universal predischarge serum bilirubin measurement to screen for risk of subsequent significant hyperbilirubinemia in the direct Coombs negative healthy term and near-term newborn during the first postnatal week.

METHODS

Total serum bilirubin (TSB) levels were obtained at the time of the routine metabolic screen in all term and near-term newborns cared for in the Pennsylvania Hospital Well Baby Nursery (n = 13 003). Postnatal age (in hours) at the time of TSB measurement was recorded. A percentile-based bilirubin nomogram for the first week was constructed from hour-specific predischarge and postdischarge TSB values of newborns (n = 2840; median BW = 3230 g and median gestational age = 39 weeks) who met classification criteria for healthy newborns (excluding those with a positive direct Coombs test or those requiring phototherapy before age 60 hours) and who were enrolled in a hospital supervised home or outpatient follow-up program. The accuracy of the predischarge TSB as a predictor of subsequent degree of hyperbilirubinemia was determined.

RESULTS

The study patients in the nomogram were racially diverse. Nearly 60% were breastfed. Predischarge, 6.1% of the study population (172/2840) had TSB values in the high-risk zone (>/=95th percentile) at 18 to 72 hours; of these, 39.5% (68/172) remained in that zone (likelihood ratio [LR] = 14.08, sensitivity = 54%; specificity = 96.2%, probability = 39.5%). Predischarge, 32.1% of the population (912/2840) had TSB values in the intermediate-risk zone. In a clinically significant minority of these newborns (58/912 or 6.4%), the postdischarge TSB moved into the high-risk zone (LR of this move: 3.2 from the upper-intermediate zone and.48 from the lower-intermediate risk zone). The predischarge TSB in 61.8% of the newborns (1756/2840) was in the low-risk zone (<40th percentile) and there was no measurable risk for significant hyperbilirubinemia (LR = 0, sensitivity = 100%; specificity = 64.7%; probability = 0%).

CONCLUSIONS

An hour-specific TSB before hospital discharge can predict which newborn is at high, intermediate or low risk for developing clinically significant hyperbilirubinemia (specifically defined as TSB levels >/=95th percentile for age in hours). Risk designation and subsequent increases or decreases of in TSB can be easily monitored on an hour-specific percentile based predictive bilirubin nomogram. A predischarge TSB measured as a universal policy would facilitate targeted intervention and follow-up in a safe, cost-effective manner. In conjunction with bilirubin practice parameter of the American Academy of Pediatrics, it could reduce the potential risk for bilirubin-induced neurologic dysfunction.

Viability assessment of mammalian sperm using SYBR-14 and propidium iodide

The proportion of living sperm in semen from six representative mammals was assessed by means of a dual staining technique using the stains SYBR-14 and propidium iodide (PI). SYBR-14, a newly developed fluorescent nucleic acid stain, maximally absorbs at 488 nm and emits at 518 nm when bound to DNA. Microscopic examination revealed that SYBR-14 stained the nuclei of living sperm bright green as determined by simultaneous examination of fluorescence and motility. Conversely, PI stained only nonmotile sperm that had lost their membrane integrity. Sperm from bulls, boars, rams, rabbits, mice, and men were stained and examined through use of fluorescence microscopy. The proportions of living and dead sperm were determined by first staining with SYBR-14 and PI and then assessing stain uptake by flow cytometry. Similar staining patterns were observed in all six mammalian species tested. Three populations of sperm were identified: living--SYBR-14 stained, dead--PI stained, and moribund--doubly stained. The SYBR-14 staining was replaced by PI staining as sperm progressed from living to moribund. The transition from green (SYBR-14) to red (PI) fluorescence started at the posterior region of the sperm head and proceeded anteriorly. The proportions of living and dead sperm in mammalian semen were readily identified through use of dual staining with SYBR-14 and PI and quantified through use of flow cytometry.

Storage of boar semen

The problems, aspects and methods of liquid storage and freeze-thawing of boar semen are discussed and a review is given on examination of spermatozoa by the recent fluorescent staining methods.

An adenovirus E1A mutant that demonstrates potent and selective systemic anti-tumoral efficacy

Replication-selective oncolytic viruses constitute a rapidly evolving and new treatment platform for cancer. Gene-deleted viruses have been engineered for tumor selectivity, but these gene deletions also reduce the anti-cancer potency of the viruses. We have identified an E1A mutant adenovirus, dl922-947, that replicates in and lyses a broad range of cancer cells with abnormalities in cell-cycle checkpoints. This mutant demonstrated reduced S-phase induction and replication in non-proliferating normal cells, and superior in vivo potency relative to other gene-deleted adenoviruses. In some cancers, its potency was superior to even wild-type adenovirus. Intravenous administration reduced the incidence of metastases in a breast tumor xenograft model. dl922-947 holds promise as a potent, replication-selective virus for the local and systemic treatment of cancer.

K-ras is an essential gene in the mouse with partial functional overlap with N-ras

Mammalian ras genes are thought to be critical in the regulation of cellular proliferation and differentiation and are mutated in approximately 30% of all human tumors. However, N-ras and H-ras are nonessential for mouse development. To characterize the normal role of K-ras in growth and development, we have mutated it by gene targeting in the mouse. On an inbred genetic background, embryos homozygous for this mutation die between 12 and 14 days of gestation, with fetal liver defects and evidence of anemia. Thus, K-ras is the only member of the ras gene family essential for mouse embryogenesis. We have also investigated the effect of multiple mutations within the ras gene family. Most animals lacking N-ras function and heterozygous for the K-ras mutation exhibit abnormal hematopoietic development and die between days 10 and 12 of embryogenesis. Thus, partial functional overlap appears to occur within the ras gene family, but K-ras provides a unique and essential function.

Streptozocin alone compared with streptozocin plus fluorouracil in the treatment of advanced islet-cell carcinoma

To evaluate the treatment of advanced islet-cell carcinoma, we randomly assigned 84 patients to streptozocin alone or streptozocin plus fluorouracil. Each regimen was given in five-day courses. The most frequent toxic effects were nausea and vomiting, mild and reversible renal toxicity, and bone-marrow depression with the combination regimen. The combination had advantages over streptozocin alone in overall rate of response (63 vs. 36 per cent) and in rates of complete response (33 vs. 12 per cent). There was no evidence of a preferential response among types of functional tumors. Objective responses were generally of long duration (median, 17 months) and of substantive clinical benefit. Treatment with the combination also yielded a survival advantage over treatment with streptozocin alone (medians, 26 and 16 1/2 months), but this difference is not statistically significant. In spite of gastrointestinal side effects, streptozocin combined with fluorouracil appears to be a valuable treatment for advanced islet-cell carcinoma.

Fusion of the nucleoporin gene NUP98 to HOXA9 by the chromosome translocation t(7;11)(p15;p15) in human myeloid leukaemia

Expression of Hoxa7 and Hoxa9 is activated by proviral integration in BXH2 murine myeloid leukaemias. This result, combined with the mapping of the HOXA locus to human chromosome 7p15, suggested that one of the HOXA genes might be involved in the t(7;11)(p15;p15) translocation found in some human myeloid leukaemia patients. Here we show that in three patients with t(7;11), the chromosome rearrangement creates a genomic fusion between the HOXA9 gene and the nucleoporin gene NUP98 on chromosome 11p15. The translocation produces an invariant chimaeric NUP98/HOXA9 transcript containing the amino terminal half of NUP98 fused in frame to HOXA9. These studies identify HOXA9 as an important human myeloid leukaemia gene and suggest an important role for nucleoporins in human myeloid leukaemia given that a second nucleoporin, NUP214, has also been implicated in human myeloid leukaemia.

Perspectives on ethnic and racial disparities in Alzheimer's disease and related dementias: Update and areas of immediate need

Alzheimer's disease and related dementias (ADRDs) are a global crisis facing the aging population and society as a whole. With the numbers of people with ADRDs predicted to rise dramatically across the world, the scientific community can no longer neglect the need for research focusing on ADRDs among underrepresented ethnoracial diverse groups. The Alzheimer's Association International Society to Advance Alzheimer's Research and Treatment (ISTAART; alz.org/ISTAART) comprises a number of professional interest areas (PIAs), each focusing on a major scientific area associated with ADRDs. We leverage the expertise of the existing international cadre of ISTAART scientists and experts to synthesize a cross-PIA white paper that provides both a concise "state-of-the-science" report of ethnoracial factors across PIA foci and updated recommendations to address immediate needs to advance ADRD science across ethnoracial populations.

Screening for Atrial Fibrillation

Approximately 10% of ischemic strokes are associated with atrial fibrillation (AF) first diagnosed at the time of stroke. Detecting asymptomatic AF would provide an opportunity to prevent these strokes by instituting appropriate anticoagulation. The AF-SCREEN international collaboration was formed in September 2015 to promote discussion and research about AF screening as a strategy to reduce stroke and death and to provide advocacy for implementation of country-specific AF screening programs. During 2016, 60 expert members of AF-SCREEN, including physicians, nurses, allied health professionals, health economists, and patient advocates, were invited to prepare sections of a draft document. In August 2016, 51 members met in Rome to discuss the draft document and consider the key points arising from it using a Delphi process. These key points emphasize that screen-detected AF found at a single timepoint or by intermittent ECG recordings over 2 weeks is not a benign condition and, with additional stroke factors, carries sufficient risk of stroke to justify consideration of anticoagulation. With regard to the methods of mass screening, handheld ECG devices have the advantage of providing a verifiable ECG trace that guidelines require for AF diagnosis and would therefore be preferred as screening tools. Certain patient groups, such as those with recent embolic stroke of uncertain source (ESUS), require more intensive monitoring for AF. Settings for screening include various venues in both the community and the clinic, but they must be linked to a pathway for appropriate diagnosis and management for screening to be effective. It is recognized that health resources vary widely between countries and health systems, so the setting for AF screening should be both country- and health system-specific. Based on current knowledge, this white paper provides a strong case for AF screening now while recognizing that large randomized outcomes studies would be helpful to strengthen the evidence base.

Revised clinical and laboratory criteria for subtypes of inherited epidermolysis bullosa. A consensus report by the Subcommittee on Diagnosis and Classification of the National Epidermolysis Bullosa Registry

Inherited epidermolysis bullosa encompasses a number of diseases, with the common finding of blister formation after minor mechanical trauma to the skin. In some forms significant, if not eventually fatal, extracutaneous disease activity may occur. In recent years application of newer technologies has contributed substantially to an overall understanding of this collection of inherited diseases. Concurrently, many new phenotypes have been recognized, in part the result of ongoing prospective patient registries in the United States and abroad. Unfortunately, this has resulted in a massive literature that may appear to be confounded by seemingly excessive or arbitrary subdivision of epidermolysis bullosa variants. With these concerns in mind a subcommittee was established by the National Epidermolysis Bullosa Registry to summarize the current literature and to make recommendations as to the best clinical and laboratory criteria for the practical diagnosis and subclassification of patients with inherited epidermolysis bullosa.

Post-operative arm morbidity and quality of life. Results of the ALMANAC randomised trial comparing sentinel node biopsy with standard axillary treatment in the management of patients with early breast cancer

This study is the first large prospective RCT of sentinel node biopsy (SNB) compared with standard axillary treatment (level I-III axillary lymph node dissection or four node sampling), which includes comprehensive and repeated quality of life (QOL) assessments over 18 months. Patients (n = 829) completed the Functional Assessment of Cancer Therapy - Breast (FACT-B+4) and the Spielberger State/Trait Anxiety Inventory (STAI) at baseline (pre-surgery) and at 1, 3, 6, 12, and 18 months post-surgery. There were significant differences between treatment groups favouring the SNB group throughout the 18 months assessment. Patients in the standard treatment group showed a greater decline in Trial Outcome Index (TOI) scores (physical well-being, functional well-being and breast cancer concerns subscales in FACT-B+4) and recovered more slowly than patients in the SNB group (p < 0.01). The change in total FACT-B+4 scores (measuring global QOL) closely resembled the TOI results. 18 months post-surgery approximately twice as many patients in the standard group compared with the SNB group reported substantial arm swelling (14% versus 7%) (p = 0.002) or numbness (19% versus 8.7%) (p < 0.001). Despite the uncertainty about undergoing a relatively new procedure and the possible need for further surgery, there was no evidence of increased anxiety amongst patients randomised to SNB (p > 0.05). For 6 months post-surgery younger patients reported less favourable QOL scores (p < 0.001) and greater levels of anxiety (p < 0.01). In view of the benefits regarding arm functioning and quality of life, the data from this randomised study support the use of SNB in patients with clinically node negative breast cancer.

Risk Factors for Coronavirus Disease 2019 (COVID-19) Death in a Population Cohort Study from the Western Cape Province, South Africa

BACKGROUND

Risk factors for coronavirus disease 2019 (COVID-19) death in sub-Saharan Africa and the effects of human immunodeficiency virus (HIV) and tuberculosis on COVID-19 outcomes are unknown.

METHODS

We conducted a population cohort study using linked data from adults attending public-sector health facilities in the Western Cape, South Africa. We used Cox proportional hazards models, adjusted for age, sex, location, and comorbidities, to examine the associations between HIV, tuberculosis, and COVID-19 death from 1 March to 9 June 2020 among (1) public-sector "active patients" (≥1 visit in the 3 years before March 2020); (2) laboratory-diagnosed COVID-19 cases; and (3) hospitalized COVID-19 cases. We calculated the standardized mortality ratio (SMR) for COVID-19, comparing adults living with and without HIV using modeled population estimates.

RESULTS

Among 3 460 932 patients (16% living with HIV), 22 308 were diagnosed with COVID-19, of whom 625 died. COVID-19 death was associated with male sex, increasing age, diabetes, hypertension, and chronic kidney disease. HIV was associated with COVID-19 mortality (adjusted hazard ratio [aHR], 2.14; 95% confidence interval [CI], 1.70-2.70), with similar risks across strata of viral loads and immunosuppression. Current and previous diagnoses of tuberculosis were associated with COVID-19 death (aHR, 2.70 [95% CI, 1.81-4.04] and 1.51 [95% CI, 1.18-1.93], respectively). The SMR for COVID-19 death associated with HIV was 2.39 (95% CI, 1.96-2.86); population attributable fraction 8.5% (95% CI, 6.1-11.1).

CONCLUSIONS

While our findings may overestimate HIV- and tuberculosis-associated COVID-19 mortality risks due to residual confounding, both living with HIV and having current tuberculosis were independently associated with increased COVID-19 mortality. The associations between age, sex, and other comorbidities and COVID-19 mortality were similar to those in other settings.

The surgical and medical perioperative complications of anterior spinal fusion surgery in the thoracic and lumbar spine in adults. A review of 1223 procedures

STUDY DESIGN

A retrospective review of 1223 thoracic and lumbar anterior spinal fusions was performed from 1969 through 1992.

OBJECTIVES

To document the incidence and specific types of perspective complications related to anterior spinal fusions.

SUMMARY OF BACKGROUND DATA

Despite the increased use of anterior spinal surgery, there has been little documentation of the specific types and frequencies of the complications associated with its use.

METHODS

All Minnesota Spine Center patients age 18 years or older who had anterior spinal fusions between the levels of T1 and S1 from August 1969 to June 1992 were reviewed for the occurrence of perioperative complications. Surgical approach and technique and associated comorbidity was recorded.

RESULTS

The risk of a complication was increased for patients over age 60 years, for women, and for patients with multiple preexisting health problems. Serious complications, such as death (0.3%), paraplegia (0.2%), and deep wound infection (0.6%) were rare. The complication rate for complications that were directly attributed to the anterior spinal surgery was 11.5%.

CONCLUSIONS

Anterior spinal fusion surgery is a safe procedure and can be used with confidence when the nature of a patient's spinal disorder dictates its use. Complications are often approach specific.

Analysis of deletions in DNA from patients with Becker and Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is an X-linked recessive genetic disorder for which the biochemical defect is as yet unknown. Recently, two cloned segments of human X-chromosome DNA have been described which detect structural alterations within or near the genetic locus responsible for the disorder. Both of these cloned segments were described as tightly linked to the locus and were capable of detecting deletions in the DNA of boys affected with DMD. In an attempt to determine more precisely the occurrence of these deletions within a large population of DMD patients and the accuracy of one of the segments, DXS164 (pERT87), in determining the inheritance of the DMD X chromosome, the subclones 1, 8 and 15 were made available to many investigators throughout the world. Here we describe the combined results of more than 20 research laboratories with respect to the occurrence of deletions at the DXS164 locus in DNA samples isolated from patients with DMD and Becker muscular dystrophy (BMD). The results indicate that the DXS164 locus apparently recombines with DMD 5% of the time, but is probably located between independent sites of mutation which yield DMD. The breakpoints of some deletions are delineated within the DXS164 locus, and it is evident that the deletions at the DMD locus are frequent and extremely large.

Leydig cell numbers, daily sperm production, and serum gonadotropin levels in aging men

Age-related changes in Leydig cell number, daily sperm production, and circulating hormone levels were studied in 15 men between 20 and 48 yr of age and 15 men between 50 and 76 yr of age. Testes and blood samples were obtained at autopsy less than 15 h after death due to trauma or heart attack. Leydig cell number was determined by quantitative histometric estimation of the proportion of glutaraldehyde-perfused, decapsulated testicular parenchyma occupied by Leydig cell nuclei of measured average volume in both testes of each subject. Daily sperm production was determined by phase contrast cytometry of round spermatid nuclei in homogenates of both fixed testes from each individual. LH, FSH, PRL, and testosterone in serum from the heart or large veins were quantified by RIA. No relationship was detected between any of the testicular or hormonal values and postmortem time. The average total number of Leydig cells was reduced by 44% in the older men and was negatively correlated with age (p = -0.62) in all men. Mean serum LH was elevated more than 2-fold in the older men and was positively correlated with age (p = +0.53) in all men. Neither serum testosterone nor serum PRL changed significantly with age. Daily sperm production was more than 50% lower in older men and was negatively correlated with age (p = -0.76) in all men. Serum FSH was more than 3-fold higher in the older men and was positively correlated with age (p = +0.72) in all men. The highest FSH levels were found in men with the lowest rates of sperm production, and FSH and daily sperm production were inversely correlated even after the effects of age were removed. These findings show that the response of the human testis to aging is variable and that the predictive value of age for most testicular characteristics is weak at the level of individual men. Nevertheless, age accounts for more than a third of the variation in Leydig cell number, and it explains more than half the variation in daily sperm production. Hence, age is the largest single contributing factor yet identified in the search for explanations underlying the variation in testicular structure and function found in groups of normal men.

Sex differences in risk factors for hiv seroconversion among injection drug users: a 10-year perspective

BACKGROUND

Injection drug use directly or indirectly accounts for nearly half the annual human immunodeficiency virus (HIV) infections in the United States. Prospective studies that investigate both sexual and parenteral HIV risks among injection drug users (IDUs) are needed. We studied factors for HIV seroconversion among male and female IDUs in Baltimore, Md.

METHODS

The HIV-negative IDUs (1447 male and 427 female) were recruited into a prospective study from 1988 to 1989 or in 1994. Participants underwent semiannual HIV tests and surveys through December 1998. Poisson regression was used to identify risk factors for HIV seroconversion, stratified by sex. Behaviors were treated as time-dependent covariates that varied at each semiannual period.

RESULTS

Subjects were primarily African American (91%), and median age at enrollment was 35 years. Incidence of HIV was 3.14 per 100 person years (95% confidence interval, 2.78-3.53) and did not significantly differ by sex. Younger age independently predicted HIV seroconversion for both men and women. Among men, factors that independently predicted HIV seroconversion were the following: less than a high school education, recent needle sharing with multiple partners, daily injection, and shooting-gallery attendance. The incidence of HIV was double for men recently engaging in homosexual activity and cocaine injection. Among women, the incidence of HIV was more than double for those recently reporting sexually transmitted diseases.

CONCLUSIONS

The incidence of HIV remained high among IDUs in Baltimore over the past decade. Risk factors for HIV seroconversion differed markedly by sex. Predominant risks among men included needle sharing and homosexual activity; among women, factors consistent with high-risk heterosexual activity were more significant than drug-related risks. Human immunodeficiency virus interventions aimed at IDUs should be sex-specific and incorporate sexual risks.

A new mechanism for induced vitamin D deficiency in calcium deprivation

Synthesis of vitamin D in the skin in response to ultraviolet light is the main determinant of vitamin D status in man and it is therefore surprising that rickets and osteomalacia, clinical signs of vitamin D deficiency, remain common in tropical and subtropical countries. Skin pigmentation can reduce vitamin D formation but this is a negligible limitation in people exposed to abundant ultraviolet light. Earlier studies in animals and man suggested that another environmental factor, the low calcium/high cereal diet typical of susceptible populations, might affect the efficiency of vitamin D utilization. We show here in rats that the rate of inactivation of vitamin D in the liver is increased by calcium deprivation. The effect is mediated by 1,25-dihydroxyvitamin D, produced in response to secondary hyperparathyroidism, which promotes hepatic conversion of vitamin D to polar inactivation products that are excreted in bile. This finding has widespread implications both for understanding the pathogenesis of endemic rickets and in that it provides a unifying mechanism for the development of vitamin D deficiency in many clinical disorders.

Human KVLQT1 gene shows tissue-specific imprinting and encompasses Beckwith-Wiedemann syndrome chromosomal rearrangements

Genomic imprinting is an epigenetic chromosomal modification in the gamete or zygote causing preferential expression of a specific parental allele in somatic cells of the offspring. We and others have identified three imprinted human genes on 11p15.5, IGF2, H19, and p57KIP2, although the latter gene is separated by 700 kb from the other two, and it is unclear whether there are other imprinted genes within this large interval. We previously mapped an embryonal tumour suppressor gene to this region, as well as five balanced germline chromosomal rearrangement breakpoints from patients with Beckwith-Wiedemann syndrome (BWS), a condition characterized by prenatal overgrowth and cancer. We isolated the upstream exons of the previously identified gene KVLQT1, which causes the familial cardiac defect long-QT (LQT) syndrome. We found that KVLQT1 spans much of the interval between p57KIP2 and IGF2, and that it is also imprinted. We demonstrated that the gene is disrupted by chromosomal rearrangements in BWS patients, as well as by a balanced chromosomal translocation in an embryonal rhabdoid tumour. Furthermore, the lack of parent-of-origin effect in LQT syndrome appears to be due to relative lack of imprinting in the affected tissue, cardiac muscle, representing a novel mechanism for variable penetrance of a human disease gene.

Wildtype Kras2 can inhibit lung carcinogenesis in mice

Although the ras genes have long been established as proto-oncogenes, the dominant role of activated ras in cell transformation has been questioned. Previous studies have shown frequent loss of the wildtype Kras2 allele in both mouse and human lung adenocarcinomas. To address the possible tumor suppressor role of wildtype Kras2 in lung tumorigenesis, we have carried out a lung tumor bioassay in heterozygous Kras2-deficient mice. Mice with a heterozygous Kras2 deficiency were highly susceptible to the chemical induction of lung tumors when compared to wildtype mice. Activating Kras2 mutations were detected in all chemically induced lung tumors obtained from both wildtype and heterozygous Kras2-deficient mice. Furthermore, wildtype Kras2 inhibited colony formation and tumor development by transformed NIH/3T3 cells and a mouse lung tumor cell line containing an activated Kras2 allele. Allelic loss of wildtype Kras2 was found in 67% to 100% of chemically induced mouse lung adenocarcinomas that harbor a mutant Kras2 allele. Finally, an inverse correlation between the level of wildtype Kras2 expression and extracellular signal-regulated kinase (ERK) activity was observed in these cells. These data strongly suggest that wildtype Kras2 has tumor suppressor activity and is frequently lost during lung tumor progression.