Search

Methods for dealing with tied event times in the Cox proportional hazards model are well developed. Also, the partial likelihood provides a natural way to handle covariates that change over time. However, ties between event times and the times that discrete time-varying covariates change have not been systematically studied in the literature. In this article, we discuss the default behavior of current software and propose some simple methods for dealing with such ties. A simulation study shows that the default behavior of current software can lead to biased estimates of the coefficient of a binary time-varying covariate and that two proposed methods (Random Jitter and Equally Weighted) reduce estimation bias. The proposed methods can be easily implemented with existing software. The methods are illustrated on the well-known Stanford heart transplant data and data from a study on intimate partner violence and smoking.

Alu repeats are short interspersed elements (SINEs) of dimeric structure whose transposition sometimes leads to heritable disorders in humans. Human cells contain a poly(A)- small cytoplasmic transcript of -120 nucleotides (nt) homologous to the left Alu monomer. Although its monomeric size indicates that small cytoplasmic Alu (scAlu) RNA is not an intermediary of human Alu transpositions, a less abundant poly(A)-containing Alu transcript of dimeric size and specificity expected of a transposition intermediary is also detectable in HeLa cells (A. G. Matera, U. Hellmann, M. F. Hintz, and C. W. Schmid, Mol. Cell. Biol. 10:5424-5432, 1990). Although its function is unknown, the accumulation of Alu RNA and its ability to interact with a conserved protein suggest a role in cell biology (D.-Y. Chang and R. J. Maraia, J. Biol. Chem. 268:6423-28, 1993). The relationship between the -120- and -300-nt Alu transcripts had not been determined. However, a B1 SINE produces scB1 RNA by posttranscriptional processing, suggesting a similar pathway for scAlu. An Alu SINE which recently transposed into the neurofibromatosis 1 locus was expressed in microinjected frog oocytes. This neurofibromatosis 1 Alu produced a primary transcript followed by the appearance of the scAlu species. 3' processing of a synthetic -300-nt Alu RNA by HeLa nuclear extract in vitro also produced scAlu RNA. Primer extension of scAlu RNA indicates synthesis by RNA polymerase III. HeLa-derived scAlu cDNAs were cloned so as to preserve their 5'-terminal sequences and were found to correspond to polymerase III transcripts of the left monomeric components of three previously identified Alu SINE subfamilies. Rodent x human somatic cell hybrids express Alu RNAs whose size, heterogeneous length, and chromosomal distribution indicate their derivation from SINEs. The coexpression of dimeric and monomeric Alu RNA in several hybrids suggests a precursor-product relationship.

When binary responses are observed over time, the dependence between observations for an individual must be considered. If the focus of a study is to identify the relationship between the binary response and a set of explanatory variables then the dependence between observations may also depend on the explanatory variables. An extension of a model where dependence is assumed to be constant will be considered. A model previously proposed for dependent binary responses will be revisited and a robust estimate of the variance-covariance matrix of coefficient estimates will be suggested to provide estimates of standard errors. The results of simulation studies investigating the properties of coefficient estimates will be discussed. An example based on a study of the AIDS epidemic and intravenous drug use behaviour will be analyzed to illustrate the techniques.

In genetic epidemiologic studies, investigators often use generalized linear models to evaluate the relationships between a disease trait and covariates, such as one or more candidate genes or an environmental exposure. Recently, attention has turned to study designs that mandate the inclusion of family members in addition to a proband. Standard models for analysis assume independent observations, which is unlikely to be true for family data, and the usual standard errors for the regression parameter estimates may be too large or too small, depending on the distribution of the covariates within and between families. The consequences of familial correlation on the study efficiency can be measured by a design effect that is equivalent to the relative information in a sample of unrelated individuals compared to a sample of families with the same number of individuals. We examine design effects for studies in association, and illustrate how the design effect is influenced by the intra-familial distribution of covariate values such as would be expected for a candidate gene. Typical design effects for a candidate gene range between 1.1 and 2.4, depending on the size of the family and the amount of unexplained familial correlation. These values correspond to a modest 10% increase in the required sample size up to more than doubling the requirements. Design effect values are useful in study design to compare the efficiency of studies that sample families versus independent individuals and to determine sample size requirements that account for familial correlation.

The present case-control study was undertaken to investigate the association between exposure to maternal hormones and risk of testicular germ-cell cancer by histologic subgroups. Cases were males, aged 16 to 59 years, diagnosed with testicular germ-cell cancer in Ontario between 1987 and 1989. Histologic review was performed on all eligible cases for the purpose of categorizing cases as seminoma or non-seminoma (the latter classified 2 ways, with and without tumors containing seminoma). Risk factor data were collected on 502 cases, 346 case mothers, 975 age-matched controls, and 522 control mothers. Exogenous hormone exposure was associated with elevated risk (OR = 4.9, 95% CI 1.7-13.9). Several additional risk factors were associated with risk of testicular cancer: bleeding and threatened miscarriage (OR = 0.6, 95% CI 0.3-1.0), maternal cigarette smoking (12+ cigarettes/day OR = 0.6, 95% CI 0. 4-1.0). pre-term birth (OR = 1.6, 95% CI 1.0-2.5), and treatment for undescended testicle (OR = 8.0, 95% CI 3.2-20.0). First births were associated with elevated risk (OR = 1.7, 95% CI 1.0-2.8) among mothers below the age of 24 years at conception. There was little evidence that risk factors differed by histologic subgroup. We found evidence that exposure to maternal hormones, particularly estrogens, is associated with testicular germ-cell cancer risk. Not only does exposure to elevated levels (exogenous hormone use, pre-term birth, and first births among young mothers) increase risk but also exposure to relatively lower levels (heavy cigarette consumption and, perhaps, bleeding and threatened miscarriage) may decrease cancer risk.

Lipopolysacharide (LPS) induced acute phase response (APR) in mouse liver leads to elevation of the low molecular weight CCAAT/Enhancer binding protein (C/EBP) beta isoform, liver-enriched transcriptional inhibitory protein (LIP). In this paper, we investigate the pathway for LIP induction during APR and the role of LIP in regulation of the C/EBPalpha promoter. The 5' region of C/EBPbeta mRNA has been shown to be involved in the regulation of LIP translation. Our data demonstrate that binding of cytoplasmic proteins to the 5' region of C/EBPbeta mRNA is altered in response to LPS administration. One of the major changes is induced binding of a cytoplasmic protein that is immunologically identical to the previously characterized RNA-binding protein CUGBP1. Induction of CUGBP1 binding activity in liver cytoplasm during APR is accompanied by the elevation of CUGBP1 binding activity on polysomes. CUGBP1 immunoprecipitated from livers of LPS-treated mice, but not from normal animals, is capable of inducing LIP translation in a cell-free translation system. The ability of CUGBP1 to induce LIP translation during APR depends on phosphorylation of CUGBP1. We show that elevation of LIP during APR and after partial hepatectomy leads to increased binding of LIP to the C/EBP consensus site found within the mouse C/EBPalpha promoter. This binding correlates with reduction of C/EBPalpha mRNA levels in both biological situations. Co-transfection experiments showed that full-length C/EBPbeta activates the C/EBPalpha promoter, while LIP blocks this activation. Our data suggest that the dominant negative isoform of C/EBPbeta, LIP, down-regulates the C/EBPalpha promoter in liver and in cultured hepatocytes. Because full-length C/EBPalpha and C/EBPbeta proteins regulate liver proliferation, this function of LIP may be important in liver growth and differentiation.

BACKGROUND: Although mass screening for osteoporosis is not recommended among postmenopausal women, there is no consensus on which women should undergo testing for low bone mineral density. The objective of this study was to develop and validate a clinical tool to help clinicians identify which women are at increased risk for osteoporosis and should therefore undergo further testing with bone densitometry. METHODS: Using Ontario baseline data from the Canadian Multicentre Osteoporosis Study, we identified all cognitively normal women aged 45 years or more who had undergone testing with dual-energy x-ray absorptiometry (DXA) at both the femoral neck and the lumbar spine (L1-L4). Participants who had a previous diagnosis of osteoporosis or were taking bone active medication other than ovarian hormones were excluded. The main outcome measure was low bone mineral density (T score of 2 or more standard deviations below the mean for young Canadian women) at either the femoral neck or the lumbar spine. Logistic regression analysis and receiver operating characteristic (ROC) analysis were used to identify the simplest algorithm that would identify women at increased risk for low bone mineral density. RESULTS: The study population comprised 1376 women, of whom 926 were allocated to the development of the tool and 450 to its validation. A simple algorithm based on age, weight and current estrogen use (yes or no) was developed. Validation of this 3-item Osteoporosis Risk Assessment Instrument (ORAI) showed that the tool had a sensitivity of 93.3% (95% confidence interval [CI] 86.3%-97.0%) and a specificity of 46.4% (95% CI 41.0%-51.8%) for selecting women with low bone mineral density. The sensitivity of the instrument for selecting women with osteoporosis was 94.4% (95% CI 83.7%-98.6%). Use of the ORAI represented a 38.7% reduction in DXA testing compared with screening all women in our study. INTERPRETATION: The ORAI accurately identifies the vast majority of women likely to have low bone mineral density and is effective in substantially decreasing the need for all women to undergo DXA testing.

Glucocorticoid action within individual cells is potently modulated by 11beta-hydroxysteroid dehydrogenase (11beta-HSD), which, by interconverting active and inert glucocorticoids, determines steroid access to receptors. Type 1 11beta-HSD (11beta-HSD1) is highly expressed in liver where it regenerates glucocorticoids, thus amplifying their action and contributing to induction of glucocorticoid-responsive genes, most of which are also regulated by members of the C/EBP (CAAT/enhancer-binding protein) family of transcription factors. Here we demonstrate that C/EBPalpha is a potent activator of the 11beta-HSD1 gene in hepatoma cells and that mice deficient in C/EBPalpha have reduced hepatic 11beta-HSD1 expression. In contrast, C/EBPbeta is a relatively weak activator of 11beta-HSD1 transcription in hepatoma cells and attenuates C/EBPalpha induction, and mice that lack C/EBPbeta have increased hepatic 11beta-HSD1 mRNA. The 11beta-HSD1 promoter (between -812 and +76) contains 10 C/EBP binding sites, and mutation of the promoter proximal sites decreases the C/EBP inducibility of the promoter. One site encompasses the transcription start, and both C/EBPalpha and C/EBPbeta are present in complexes formed by liver nuclear proteins at this site. The regulation of 11beta-HSD1 expression, and hence intracellular glucocorticoid levels, by members of the C/EBP family provides a novel mechanism for cross-talk between the C/EBP family of transcription factors and the glucocorticoid signaling pathway.

For the simulated data of GAW11, the roles of two environmental factors, E1 and E2, were investigated. Logistic regression analyses measuring the association between outcome (either mild or severe disease versus no disease) and E1 and E2 exposure indicated that E1 was a risk factor for disease (either mild or severe) but that E2 was not associated with outcome. Linkage analyses were performed for strata defined by E1 and E2 exposure. A specific disease locus was identified in these stratified analyses where this locus would not have been identified with an unstratified linkage analysis. Finally, stratified generalized transmission disequilibrium test analyses yielded several false positive results.

The aim of this investigation was to examine the relationship between Class II HLA antigens and disease expression in systemic lupus erythematosus (SLE). HLA-DR and DQ antigen frequency was studied serologically in 217 SLE patients followed prospectively and compared to 320 healthy controls. The relationship between HLA antigens and the presence of disease manifestations, as well as death was investigated in 117 SLE patients enrolled within the first year of their disease. A univariate analysis confirmed the association between HLA-DR3 and SLE. HLA antigen DR1, DR6, DR7, DQw1 and DQw3 were decreased in patient group compared to the controls. A logistic regression model showed a significantly negative association with HLA-DR1, DR6 and DR7, and a positive association with HLA-DR3. The reduced frequency of HLA-DQw1 and DQw3 was maintained using a logistic procedure. Cox Proportional Hazards models revealed no association between HLA-Class II antigens and death. Logistic regression models revealed no associations between central nervous system (CNS) disease nor musculoskeletal manifestations with any of the DR antigens. There was a trend towards a lower frequency of HLA-DR6 in patients with renal involvement and lower prevalence of HLA-DR1 and HLA-DR7 in patients with vasculitis.

Both CCAAT/enhancer binding protein alpha (C/EBPalpha) and C/EBPbeta are intronless, yet can create various N-terminally truncated protein products with distinct DNA binding and transactivation potentials. These proteins can be generated via two distinct mechanisms, one translational and the other post-translational. In the translational mechanism, there is alternative translational start site selection of the different AUG codons present in the single messenger RNA (mRNA) species via a process of leaky ribosome scanning. Additionally, a post-translational method of isoform formation, through specific proteolytic cleavage of the full length protein has also been described. In this manuscript, we present evidence that the production of C/EBPbeta protein isoforms in the neonatal mouse liver is regulated by C/EBPalpha. In C/EBPalpha knockout mice, the predominant C/EBPbeta proteins are the larger 38- and 35-kd isoforms, whereas wild-type animals primarily possess the smaller 21- and 14-kd isoforms. These C/EBPalpha-dependent differences are liver specific, not present in lung or adipose tissues, and present at day 18 of development. Additionally, we show that induction of C/EBPalpha expression leads to an increase in the production of the 21-kd C/EBPbeta isoform in cell culture studies. As the various C/EBPbeta protein isoforms have different transcriptional capabilities, it is important to understand the regulation of the production of these isoforms. Our observations suggest a novel role for the C/EBPalpha transcription factor in this process.

The CCAAT/enhancer binding protein alpha (C/EBP alpha) binds to specific promoter sequences and directs transcription of many genes expressed in the liver. Overexpression of C/EBP alpha in established cell lines inhibits cell proliferation. Primary hepatocytes from newborn C/EBP alpha(-/-) mice and normal littermates were used to determine whether the absence of C/EBP alpha increased proliferation and/or transformation of these cells in vitro. DNA synthesis, as measured by bromodeoxyuridine (BrdU) incorporation 24 hours postharvest, was fourfold higher in cells from C/EBP alpha(-/-) pups. Established cell lines were derived from 7 of 8 hepatocyte cultures initiated from null mutants, 4 of 23 cultures from heterozygotes, and 0 of 12 cultures from wild-type animals. C/EBP alpha(-/-) cultures had epithelial morphology, showed bile canaliculi, and expressed albumin messenger RNA (mRNA). When cultured on Matrigel, which promotes differentiation, cell lines derived from C/EBP alpha(-/-) mice formed cords and increased albumin mRNA expression by 1.7- to 3.8-fold. C/EBP alpha(-/-) cell lines exhibited rapid growth and rapid accumulation of chromosomal abnormalities, and were capable of forming nodules when inoculated into the abdominal subcutaneous tissue of nude mice. Our data show that C/EBP alpha is an important regulator of hepatocyte proliferation and participates in the maintenance of the nontransformed hepatic phenotype in vitro.

Previous studies have indicated that C/EBP alpha is involved in the regulation of factor IX and mutations of a C/EBP recognition element in the factor IX promoter result in haemophilia B. We now report that mice homozygous for the deletion of the c/ebp alpha gene are significantly deficient in factor IX transcription.

Modern genetics has developed methods to modify the expression of genes in animals to study the factors responsible for the tissue-specific expression and hormonal and dietary regulation of metabolic processes. As these methods are applied to genes that code for critical proteins in metabolic pathways, a new insight into the control of metabolism is emerging. There are three general approaches currently in use. First, is the introduction of genes into the germ line to create transgenic animal models in which the gene of interest is over-expressed. This model is of particular value for promoter analysis because it is possible to introduce specific mutations into a putative regulatory region of a transgene and study its transcriptional control in the intact animal. Second, the developmental function of a gene product and its effect on various metabolic processes in a mouse can be directly determined by deleting a gene of interest by homologous recombination. Gene "knockout" mice are currently available with deletions in the genes for a variety of transcription factors and other biologically active proteins, permitting a critical analysis of the proteins responsible for the metabolic patterning of the animal. Third, the metabolic role of a gene of interest in a specific tissue can be studied by ablating its mRNA by the introduction of a transgene that codes for antisense mRNA targeted against the gene transcript. Because it is possible to use a transgene with a tissue-specific promoter, this procedure allows the isolation of the metabolic effect to a selected tissue in the transgenic animal. Taken together, these procedures provide a unique set of metabolic models for an in-depth study of metabolic regulation. This review will present examples of selected animal models currently available and will outline the challenge these animals present for investigators in the nutritional sciences.

Two analytic methods were used in the Problem 2 data set. First, generalized estimating equations (GEE) modelling was developed to adjust for familial correlation in regressions evaluating candidate genes and an environmental factor. Second, the affected-pedigree-member (APM) method was used to identify chromosomal regions of interest and linkage of candidate genes with disease affection status. The GEE method identified C5 (MG1) as important for the quantitative trait Q1 and the corresponding affection status DIS, but the APM method was only suggestive. The GEE method identified C2 (MG2) as important for Q2 but only marginally important for Q1 and not important for DIS.

HNF1 and C/EBP alpha are transcription factors that bind to and trans-activate the human albumin gene proximal promoter. Various 5' deletions of the human albumin promoter were coupled to a luciferase reporter gene (alb-luc constructs) and co-electroporated with HNF1 and/or C/EBP alpha expression vectors into HeLa cells. Luciferase activities from co-electroporation of the HNF1 and C/EBP alpha expression vectors with the alb-luc constructs were approximately 10-fold greater than the sum of the activities achieved with HNF1 and C/EBP alpha alone. Analysis of COOH-terminal or internal deletions of the HNF1 expression vector revealed that the domain important for collaborative interaction with C/EBP alpha could be localized to a 157 amino acid region not previously described. This domain is proline and glutamine-rich and is highly homologous (66%) to a portion of vHNF1, an evolutionarily related gene first identified in dedifferentiated hepatoma cells. A construct linking the negatively charged activation domain of herpes simplex virus protein VP16 to the DNA-binding domain of HNF1 showed that it could also synergize with C/EBP alpha to trans-activate the human albumin gene promoter. Our studies delineate a domain in HNF1 important for synergistic activation with C/EBP alpha.

Research in cellular transplantation is frequently compromised by an inability to identify transplanted cells engrafting into orthotopic sites if they exhibit normal morphology and no unique antigenic markers. A method is described for using the fluorescent dye DiI as a marker for cell transplantation studies. This dye is not metabolized or exchanged between cells in vitro or in vivo and enables identification of engrafted cells by fluorescence microscopy, flow cytometry or fluorescence-activated cell sorting. Applications are described in autologous hepatocellular and thyroid follicular cell transplantation.

HLA antigen distribution was studied in 126 patients with systemic sclerosis (SSc) followed prospectively and compared to that of 325 healthy controls. The frequencies of HLA antigens DR3, DR5 and DRw52 were increased in patients with diffuse skin involvement (P = 0.02, 0.05, 0.03). The presence of DRw52 (relative risk [RR] much much greater than 1) and DRw6 (RR = 54.5) was associated with significantly increased risks of a fatal disease outcome with pulmonary hypertension (PHT). In the absence of PHT, DRw252 was inversely associated with the risk of death. These findings indicate an adverse prognosis in SSc when PHT is present in association with DRw52.

Orthotopic liver transplantation (OLT) represents the only therapeutic option for many patients with end-stage liver disease as well as many inborn genetic errors of hepatic metabolism. Despite dramatic progress in methods for OLT, the utilization of this procedure is limited by its considerable morbidity and mortality, by a chronic shortage of organs for transplant, and by difficulty arranging funding for many patients. Many children with fulminant hepatic failure do not receive OLT because this technology is unavailable or unaffordable. Hepatocellular transplantation (HCT), in which isolated, heterologous hepatocytes from a donor liver would be infused into the diseased organ in order to provide essential hepatic functions, could provide a much needed therapeutic alternative to OLT in the treatment of some causes of hepatic insufficiency. Experiments in animals have demonstrated that several genetic deficiencies of hepatic metabolism as well as experimental induced hepatic failure in animals can be reversed by HCT. Despite this experience, HCT has never been attempted in human subjects. This protocol represents the first proposed clinical trial of HCT. We are proposing a clinical trial in which HCT would be attempted as a therapeutic intervention in children with acute hepatic failure who have no other medical or surgical options. This proposal is intended to establish surgical methods for HCT and to evaluate the feasibility of this procedure for treating hepatic disease in humans. It is our expectation that HCT may provide short-term support for patients awaiting organ availability, a "bridge to recovery" allowing patients with fulminant hepatic failure to recover, or a long-term repopulation of the patient's liver with healthy donor cells. One of the major limitations of many animal studies in HCT is that, since the donor hepatocytes are often indistinguishable from those of the host, it has often been difficult to demonstrate a clear correlation between engraftment and the therapeutic effect. In order to verify engraftment independent of the therapeutic response, we propose to "mark" the donor hepatocytes by transducing these cells with a recombinant retroviral vector (LNL6) carrying a marker gene (NEO-R, neomycin phosphoribosyl transferase). The presence of this marker will enhance the ability to identify transplanted cells in the host using assays for the NEO-R gene or transcribed NEO-R mRNA. The LNL6 vector has been approved for human use and has been used as a marker gene for transplanted cells in human subjects without any reported adverse effects. We would like to emphasize that this is a proposal with therapeutic intent.(ABSTRACT TRUNCATED AT 400 WORDS)

A link between the HLA system and disease susceptibility can be assessed through the observation of families containing two or more affected siblings. Departures from Mendelian inheritance of the parental haplotypes among the affected siblings are an indication of such a relationship. Other variables, such as environmental factors, may also be related to disease susceptibility. An approach to examining the degree of haplotype sharing and the effect of other variables of interest on observed sharing is presented and two examples analyzed.

Previous studies have indicated that C/EBPα is involved in the regulation of factor IX and mutations of a C/EBP recognition element in the factor IX promoter result in haemophilia B. We now report that mice homozygous for the deletion of the c/ebpα gene are significantly deficient in factor IX transcription.

A link between the HLA system and disease susceptibility can be assessed through the observation of families containing two or more affected siblings. Departures from Mendelian inheritance of the parental haplotypes among the affected siblings are an indication of such a relationship. Other variables, such as environmental factors, may also be related to disease susceptibility. An approach to examining the degree of haplotype sharing and the effect of other variables of interest on observed sharing is presented and two examples analyzed.

The tissue-specific expression of two types of mouse amylase genes does not overlap in vivo; the Amy-1 locus is transcribed in the parotid gland and the liver, while expression of Amy-2 is limited to the pancreas. We identified a mouse hepatoma cell line, Hepa 1-6, in which both amylase genes can be simultaneously expressed. Amy-1 is constitutively active in these cells and is inducible by dexamethasone at the level of mRNA. We demonstrated that the liver-specific promoter of Amy-1 is utilized by the dexamethasone-treated hepatoma cells, and that glucocorticoid consensus sequences are present upstream of this promoter. Amy-2 is not detectable constitutively, but can be activated if the cells are cultured in serum-free medium containing dexamethasone. Expression of Amy-2 in a nonpancreatic cell type has not previously been observed. We speculate that induction of Amy-1 and activation of Amy-2 may involve different regulatory mechanisms. Hepa 1-6 cells provide an experimental system for molecular analysis of these events.

The impaired response to mitogens of lymphocytes from old persons has been shown to result from the presence of fewer responsive cells and the failure of these cells to divide normally after stimulation. We present additional evidence that the successive divisions of mitogen-responsive lymphocytes from old people are impaired. We labeled sister chromatids with BrdU and identified cells that were dividing for the first, second, or third time in culture. This analysis showed that lymphocyte cultures from old people contained only one-half the number of lymphocytes dividing for a second time and less than one-quarter the number of cells dividing for a third time compared with lymphocyte cultures from young people. It was shown that these changes reflected an absolute decrease in the number of second and third generation cells in cultures from old persons. No alterations in the cytokinetics of proliferation by lymphocytes from old people were found. These results provide additional evidence that mitogen-responsive lymphocytes from healthy elderly people do not undergo as many divisions in cultures with PHA as do lymphocytes from young persons.

Mouse hepatoma cells were established in vitro as a permanently growing line designated Hepa. The mass population and a subclone were characterized for their karyotype and their retention of liver-specific properties. An examination of 17 hepatic traits revealed that the cell lines secreted several serum proteins. The activities of a number of liver-specific enzymes, however, appeared to be absent in these cells. The identification of differentiated properties of cultured hepatoma cells permits the use of these lines in a variety of studies such as cell hybridization, biochemical analysis of tissue-specific gene products, and the modulation of expression of genes governing differentiated phenotypes. This report presents the analysis of a broad spectrum of characteristics and thereby describes one of the most fully defined hepatoma cell lines of murine origin in the literature.

To test the hypothesis that widespread errors in protein synthesis underlie diseases with features resembling premature aging, we examined the thermostability of two erythrocyte enzymes in three unrelated progeria families and in two Werner syndrome patients. Unlike previous reports, no increased heat-labile component of glucose-6-phosphate dehydrogenase (G6PD) or 6-phosphogluconate dehydrogenase (6PGD) was found. Our results do not support the protein error hypothesis. Our data raise questions regarding the usefulness of thermolabile enzyme level as a proposed marker for progeria or Werner syndrome.