The development of methods for assessing the in vivo oestrogen-like effects of xenobiotics in CD-1 mice

The increasing awareness and concern about the potential health risks posed to the ecosystem and to man by endocrine disrupting chemicals with oestrogen-like activity in the environment has focused attention on the need for developing sensitive and specific methods for identifying these xenobiotics and to evaluate their degrees of toxic effects. We have conducted dose response studies in immature (21 days old) CD-1 female mice treated with four compounds, diethylstilboestrol (DES) (0.1 microg to 25 mg/kg body weight), alpha-zearalanol (0.5 mg to 25 mg/kg body weight), methoxychlor (0.5 mg to 500 mg/kg body weight) and bisphenol A (10 microg to 100 mg/kg body weight) administered subcutaneously daily for 3 days, and measured a number of uterine markers in treated and control (vehicle treated) mice. These were, in addition to the commonly measured changes in relative uterus weight and histopathological examination of uterine tissue, three other markers indicative of uterotrophic effects, namely, uterine luminal epithelium BrdU labelling index over the last 24 hr, peroxidase activity and lactoferrin expression. All of these markers showed clear dose-related increases in DES- and methoxychlor-treated animals. In the case of alpha-zearalanol treatment, relative uterine weight, peroxidase activity and lactoferrin expression showed dose-related increases at all the doses investigated. BrdU incorporation (an index of cell proliferation) also progressively increased at dose levels ranging from 0.1 mg to 5.0 mg/kg body weight, but apparently decreased at 25 mg/kg body weight. In contrast to these findings, bisphenol-A treatment showed no consistent changes in any of the four markers at the dose levels investigated. Additionally, studies were also conducted on a number of chemicals in CD-1 mice at one dose level. The chemicals investigated were: bisphenol A (1 g/kg body weight/day), naringenin (1 g/kg body weight/day) o,p'-DDT (500 mg/kg body weight/day), genistein (1 g/kg/day), coumestrol (0.5 mg/kg/day) and chlordecone (20 mg/kg/day) administered subcutaneously daily for 3 days. There was some variability in response of the markers perhaps indicating that the chemicals did not all act in the same way. The findings of our exploratory in vivo studies in CD-1 mice suggest that the measurement of a range of uterine markers, in addition to organ weight and histopathology, would provide useful information on the potential oestrogenicity of chemicals.

Quantitative expression of Oct-3/4 defines differentiation, dedifferentiation or self-renewal of ES cells

Cell fate during development is defined by transcription factors that act as molecular switches to activate or repress specific gene expression programmes. The POU transcription factor Oct-3/4 (encoded by Pou5f1) is a candidate regulator in pluripotent and germline cells and is essential for the initial formation of a pluripotent founder cell population in the mammalian embryo. Here we use conditional expression and repression in embryonic stem (ES) cells to determine requirements for Oct-3/4 in the maintenance of developmental potency. Although transcriptional determination has usually been considered as a binary on-off control system, we found that the precise level of Oct-3/4 governs three distinct fates of ES cells. A less than twofold increase in expression causes differentiation into primitive endoderm and mesoderm. In contrast, repression of Oct-3/4 induces loss of pluripotency and dedifferentiation to trophectoderm. Thus a critical amount of Oct-3/4 is required to sustain stem-cell self-renewal, and up- or downregulation induce divergent developmental programmes. Our findings establish a role for Oct-3/4 as a master regulator of pluripotency that controls lineage commitment and illustrate the sophistication of critical transcriptional regulators and the consequent importance of quantitative analyses.

Once-daily versus multiple-daily gentamicin in empirical antibiotic therapy of febrile neutropenia following intensive chemotherapy

The clinical efficacy and toxicity of once-daily compared with multiple-daily gentamicin dosing, in combination with azlocillin, were studied retrospectively in febrile neutropenic episodes following intensive chemotherapy. Fifty-two episodes were studied in 28 patients with acute myeloid leukaemia. Reasons for initiation of antibiotic therapy, dose, duration of treatment, organism isolation rates, response, cost comparison and toxicity were studied in the two treatment groups. The main indication for initiation of antibiotic therapy was neutropenic fever without a documented infection (80.8% of episodes). The response rate to once-daily gentamicin dosing and azlocillin was three times higher than to multiple-daily gentamicin dosing and azlocillin (P = 0.0112). The incidence of toxicity was low overall and was slightly but not significantly higher in the once-daily group. In this clinical context once-daily gentamicin at a dose of 7 mg/kg/day is more effective than a multiple-daily dosing regimen but may be more toxic.

Preliminary evidence of an association of tumour necrosis factor microsatellites with increased risk of multiple basal cell carcinomas

Tumour necrosis factor alpha (TNF-alpha) appears important in ultraviolet-induced immunosuppression, suggesting that it is a susceptibility candidate for cutaneous basal cell carcinoma (BCC). We now describe data on the association between TNF microsatellite polymorphisms, first on susceptibility in 202 controls and 133 cases each having two to 30 BCCs, and secondly, within the cases, on BCC numbers. The data show that the proportions of individuals with TNF a1- and a7-containing genotypes were significantly different (P = 0. 0271, P = 0.0393, respectively) between cases and controls. Secondly, within the cases, TNF alleles d4 (P = 0.023) and d6 (P = 0.006) alone, and the TNF a2-b4-d5 haplotype (P = 0.007), were significantly associated with the number of BCC lesions. These preliminary data provide the first evidence that TNF microsatellite polymorphism may influence the pathogenesis of multiple BCC.

Vitamin D receptor polymorphisms are associated with altered prognosis in patients with malignant melanoma

Calcitriol [1,25(OH)2D3], the hormonal derivative of vitamin D3, is an antiproliferative and prodifferentiation factor for several cell types, including cultured melanocytes and malignant melanoma (MM) cells. Several polymorphisms of the vitamin D receptor (VDR) gene have been described including a FokI RFLP in exon 2, BsmI, and ApaI polymorphisms in intron 8 and an adjacent TaqI RFLP in exon 9. Alterations in vitamin D/1,25(OH)2D3 levels and polymorphisms of the VDR have been shown to be associated with several systemic malignancies. We hypothesize that polymorphism in this gene may be associated with altered susceptibility and outcome in patients with MM. A hospital-based case-control study, using 316 MM cases and 108 controls, was used to assess associations with MM susceptibility. Breslow thickness, the most important single prognostic factor in MM, was used as the outcome measure. Polymorphisms at the FokI and TaqI restriction sites were determined using PCR-based methods. Polymorphism at the FokI, but not TaqI, RFLP was associated with an altered risk of MM (P = 0.014). More importantly, variant alleles were associated with increased Breslow thickness. Thus, homozygosity for variant alleles at both RFLP (ttff genotype combination) was significantly associated with thicker tumors. (> or = 3.5 mm; P = 0.001; odds ratio = 31.5). Thus, polymorphisms of the VDR gene, which would be expected to result in impaired function, are associated with susceptibility and prognosis in MM. These data suggest that 1,25(OH)2D3, the ligand of the VDR, may have a protective influence in MM, as has been proposed for other malignancies.

HLA class I and class II profiles of patients presenting with Sydenham's chorea

Sydenham's chorea (SC) may occur in rheumatic fever (RF) patients without arthritis and carditis. In this study we typed HLA antigens and alleles in patients presenting with the distinct major clinical manifestations of RF, i.e., chorea, carditis, or arthritis, in population and family studies. We evaluated 91 patients with RF for HLA-A, HLA-B, and HLA-DR antigens; of these, 33 had pure chorea, 26 pure carditis, 16 pure arthritis, and 16 carditis plus arthritis. We also typed 24 SC patients and their unaffected siblings for HLA-DRB1 and HLA-DQB1 alleles using molecular methods. HLA-B49 and HLA-DR1 antigens were overrepresented in the total group of patients with RF and in all the subgroups studied, excluding the SC subgroup in which the frequency of HLA-DR1 antigen was not increased. The frequencies of the HLA-DRB1 and HLA-DQB1 alleles in patients with pure chorea were not significantly different from those observed in controls. Similarly, the frequencies of HLA class II alleles in SC patients did not differ significantly from those observed in unaffected siblings. These findings show that immunogenetic susceptibility to RF varies according to the major clinical manifestation presented by the patient.

Genetic variation of basal iron status, ferritin and iron regulatory protein in mice: potential for modulation of oxidative stress

Toxic and carcinogenic free radical processes induced by drugs and other chemicals are probably modulated by the participation of available iron. To see whether endogenous iron was genetically variable in normal mice, the common strains C57BL/10ScSn, C57BL/6J, BALB/c, DBA/2, and SWR were examined for major differences in their hepatic non-heme iron contents. Levels in SWR mice were 3- to 5-fold higher than in the two C57BL strains, with intermediate levels in DBA/2 and BALB/c mice. Concentrations in kidney, lung, and especially spleen of SWR mice were also greater than those in C57BL mice. Non-denaturing PAGE of hepatic ferritin from all strains showed a major holoferritin band at approximately 600 kDa, with SWR mice having > 3-fold higher levels than C57BL strains. SDS PAGE showed a band of 22 kDa, mainly representing L-ferritin subunits. A trace of a subunit at 18 kDa was also detected in ferritin from SWR mice. The 18 kDa subunit and a 500 kDa holoferritin from which it originates were observed in all strains after parenteral iron overload, and there was no major variation in ferritin patterns. Although iron uptake studies showed no evidence for differential duodenal absorption between strains to explain the variation in basal iron levels, acquisition of absorbed iron by the liver was significantly higher in SWR mice than C57BL/6J. As with iron and ferritin contents, total iron regulatory protein (IRP-1) binding capacity for mRNA iron responsive element (IRE) and actual IRE/IRP binding in the liver were significantly greater in SWR than C57BL/6J mice. Cytosolic aconitase activity, representing unbound IRP-1, tended to be lower in the former strain. SWR mice were more susceptible than C57BL/10ScSn mice to the toxic action of diquat, which is thought to involve iron catalysis. If extrapolated to humans, the findings could suggest that some people might have the propensity for greater basal hepatic iron stores than others, which might make them more susceptible to iron-catalysed toxicity caused by oxidants.

A structurally defined mini-chromosome vector for the mouse germ line

Yeast artificial mini-chromosomes have helped to define the features of chromosome architecture important for accurate segregation and replication and have been used to identify genes important for chromosome stability and as large-fragment cloning vectors. Artificial chromosomes have been developed in human cells but they do not have defined, experimentally predictable structures. Fragments of human chromosomes have also been introduced into mice and in one case passed through the germ line. In these experiments, however, the structure and sequence organization of the fragments was not defined. Structurally defined mammalian mini-chromosome vectors should allow large tracts of DNA to be introduced into the vertebrate germ line for biotechnological purposes and for investigations of features of chromosome structure that influence gene expression. Here, we have determined the structure and sequence organization of an engineered mammalian mini-chromosome, ST1, and shown that it is stably maintained in vertebrate somatic cells and that it can be transmitted through the mouse germ line.

CYP1A2 is essential in murine uroporphyria caused by hexachlorobenzene and iron

Using Cyp1a2(-/-) mice we previously showed that CYP1A2 is absolutely required for hepatic uroporphyrin accumulation caused by iron and 5-aminolevulinate (ALA) treatment, both in the presence and absence of an inducer of CYP1A2. In this study we have used these mice to investigate whether CYP1A2 has an obligatory role in hepatic uroporphyria caused by hexachlorobenzene (HCBZ), an inducer of CYP2B and CYP3A, as well as CYP1A2. Here we treated mice with HCBZ and iron, with and without the porphyrin precursor, ALA, in the drinking water. In iron-loaded wild-type mice given a single dose of HCBZ and ALA, hepatic uroporphyrin (URO) accumulated to 300 nmol/g liver after 37 days, whereas in Cyp1a2(-/-) mice, there was no hepatic URO, even after an additional dose of HCBZ, and a further 29 days of ALA treatment. A similar requirement for CYP1A2 was found in uroporphyria produced in HCBZ and iron-treated mice in the absence of ALA. As detected by Western immunoblotting, HCBZ induced small increases in CYP2B and CYP3A in the livers of all animals. In the wild-type animals, HCBZ also induced CYP1A2 and associated enzyme activities, including uroporphyrinogen oxidation, by about 2-3-fold. In the Cyp1a2(-/-) mice, HCBZ did not increase hepatic microsomal uroporphyrinogen oxidation. These results indicate that, in mice, CYP1A2 is essential in the process leading to HCBZ-induced uroporphyria. Contributions by other CYP forms induced by HCBZ appear to be minimal.

Detoxifying enzyme genotypes and susceptibility to cutaneous malignancy

While ultraviolet (UV) exposure is thought to be a major risk factor for basal cell carcinoma (BCC) and squamous cell carcinoma, more recent research has focused on genetic factors predisposing to these cancers. UV constitutes an oxidative stress with generation of free radicals, leading to lipid and DNA damage and gene mutation. It could therefore be hypothesized that individual ability to deal with these products may be important in cutaneous carcinogenesis. It is clear from recent studies that polymorphisms in detoxifying enzyme genes are important in determining susceptibility to skin cancer. The magnitude of effect in BCC is similar to that seen with many other previously described risk factors. However, uncertainties exist regarding the phenotypic consequences of some of these polymorphisms and relevant substrates. This review describes the influence of polymorphisms in detoxifying enzymes in determining susceptibility to skin cancer (in particular to BCC) and give a brief overview of the biochemistry of the detoxification process.

Common extensor tendon rupture following corticosteroid injection for lateral tendinosis of the elbow

Corticosteroid injections are commonly administered to athletes to relieve symptoms of lateral elbow tendinosis. This report presents a case of almost total rupture of the common extensor origin in a 45 year old female squash player secondary to such a procedure.

Correlation between disparity for the minor histocompatibility antigen HA-1 and the development of acute graft-versus-host disease after allogeneic marrow transplantation

Results of a previous study suggested that recipient mismatching for the minor histocompatibility antigen HA-1 is associated with acute graft-versus-host disease (GVHD) after allogeneic marrow transplantation. In that study, most patients received either cyclosporine or methotrexate for GVHD prophylaxis, and a cytotoxic T-cell clone was used to test for HA-1 disparity. To facilitate large-scale testing, we developed a method that uses genomic DNA to identify HA-1 alleles. A retrospective study was conducted to correlate HA-1 disparity and the occurrence of acute GVHD in 237 HLA-A2-positive white patients who had received a marrow or peripheral blood stem cell transplant from an HLA-identical sibling. All patients received both methotrexate and cyclosporine for GVHD prophylaxis. The presence of HLA-A*0201 was confirmed in 34 of the 36 HA-1 disparate pairs by sequencing the HLA-A locus. Grades II-IV GVHD occurred in 22 (64.7%) of these 34 patients, compared with 86 (42.8%) of the 201 patients without HA-1 disparity (odds ratio, 2. 45; 95% confidence interval [CI], 1.15 to 5.23; P =.02). Recipient HA-1 disparity showed a trend for association with acute GVHD (odds ratio, 2.1; 95% CI, 0.91 to 4.68; P =.08) when a multivariable logistic regression model was used to include additional risk factors. These data are consistent with results of the previous study, suggesting an association between HA-1 disparity and risk of acute GVHD, but the strength of this association may be lower in patients who received both methotrexate and cyclosporine than in those who received methotrexate or cyclosporine alone.

Changes in excitability of motor cortical circuitry in primary restless legs syndrome

OBJECTIVE

To investigate the excitability of segmental and suprasegmental systems in patients with primary restless legs syndrome (pRLS) by measuring the cortical silent period (C-SP) and the peripheral silent period (P-SP).

BACKGROUND

There is some evidence that RLS may be the motor manifestation of normal CNS periodicity that becomes disinhibited under certain conditions. The mechanism of this disinhibition is unclear.

DESIGN/METHODS

Ten patients with pRLS and 10 normal age-matched subjects were studied. The mixed nerve P-SP produced by electrical stimulation of the median and common peroneal nerves was recorded during maximal contraction of the abductor pollicis brevis (APB) and tibialis anterior (TA) muscles. The C-SP produced by a single magnetic shock to motor cortex at 150% of resting threshold was also measured during maximal contraction of the APB and TA muscles. The average of 5 to 10 trials at each site was obtained and compared using Student's t-test.

RESULTS

Resting central motor threshold was not significantly different between pRLS patients and the control group. The average duration of the C-SP was shorter in the APB (74.5+/-37.7 versus 129.56+/-35.95 msec, p<0.05) and TA (66.81+/-25.63 versus 136.1+/-40.35 msec, p<0.05) in patients with pRLS. The P-SP duration, however, was not significantly different between two groups in either limb.

CONCLUSION

The supraspinal inhibitory system is impaired in pRLS.

Persistent health effects of dioxin contamination in herbicide production

A total of 159 cases of chloracne reported in 1969-1975 in TCDD-contaminated production of the herbicide 2,4,5-T have been followed for mortality and morbidity up to 1996 when blood and urine tests were performed on 50 survivors of these exposed chemical workers and matched controls. In exposed, the most frequent cause of sick leave was chloracne which persisted in 32%. Neurological symptoms were reported frequently (44% sleep disturbance, 32% headache, 30% neuralgia). BSR, leucocytes, gamma-GT, SGOT, and SGPT were significantly higher in exposed than in controls. The effects of exposure (P= 0.002) and alcohol (P= 0.002) on gamma-GT were found to be independent of each other. Comparisons within the chloracne cohort showed significantly exposed TCDD per gram blood lipid in patients with a history of liver disease (mean 801 pg/g) than without (mean 407 pg/g). Other congeners were not found elevated but some higher chlorinated furans and PCBs were found reduced in patients with liver disease. In multiple regression analysis with the factors age, alcohol, and log TCDD, the effects of TCDD and its interaction with age were found significant, indicative of chronic liver damage after high TCDD exposure at a young age. The prevalence of neurological symptoms and signs of chronic liver disease were related to TCDD in blood and abnormal poryphyrins in urine. In 48% coproporphyrin I > III ratio was elevated, this group showing increased TCDD (mean 719 pg/g). These results contribute to the evidence that chloracne is not the only chronic disease which can be related to TCDD exposure, even 23 years after exposure and despite high intersubject variability of TCDD half-life and other exposures.

A comparison of two commercial quantitative electromyographic algorithms with manual analysis

Quantitative EMG (QEMG) is a useful technique in the evaluation of neuromuscular disease. Manual waveform measurements have been replaced by automated computer-based measurements, but there is no uniformity in computer algorithms used to make waveform measurements. We compared QEMG measurements made by algorithms in two commercially available EMG machines with manual measurements. Motor unit action potentials (MUAPs) were simultaneously fed into the two machines and analyzed using QEMG default settings and automatic waveform marking. The averaged MUAPs were also manually marked. The two algorithms and manual marking did not differ significantly for MUAP amplitude. There were significant differences between algorithms for duration and number of phases. Our study indicates that, although automated algorithms make QEMG more practical, visual inspection, and remarking of each MUAP if needed, is necessary before making clinical judgments from the data.

Leukemia inhibitory factor and its receptor promote adipocyte differentiation via the mitogen-activated protein kinase cascade

Extracellular factors and intracellular signaling pathways involved in early events of adipocyte differentiation are poorly defined. It is shown herein that expression of leukemia inhibitory factor (LIF) and LIF receptor is developmentally regulated during adipocyte differentiation. Preadipocytes secrete bioactive LIF, and an antagonist of LIF receptor inhibits adipogenesis. Genetically modified embryonic stem (ES) cells combined with culture conditions to commit stem cells into the adipocyte lineage were used to examine the requirement of LIF receptor during in vitro development of adipose cells. The capacity of embryoid bodies derived from lifr(-/-) ES cells to undergo adipocyte differentiation is dramatically reduced. LIF addition stimulates adipocyte differentiation of Ob1771 and 3T3-F442A preadipocytes and that of peroxisome proliferator-activated receptor gamma2 ligand-treated mouse embryonic fibroblasts. Expression of the early adipogenic transcription factors C/EBPbeta and C/EBPdelta is rapidly stimulated following exposure of preadipose cells to LIF. The selective inhibitors of mitogen-activated protein kinase kinase, i.e. PD98059 and U0126, inhibit LIF-induced C/EBP gene expression and prevent adipocyte differentiation induced by LIF. These results are in favor of a model that implicates stimulation of LIF receptor in the commitment of preadipocytes to undergo terminal differentiation by controlling the early expression of C/EBPbeta and C/EBPdelta genes via the mitogen-activated protein kinase cascade.

New prospects for human stem-cell therapy in the nervous system

It would be of enormous benefit if human neural tissue could be generated in vitro as this would allow screening for neuroactive compounds, and provide a source of tissue for testing cellular and gene therapies for CNS disorders. It is now well established that pluripotent embryonic stem cells (ES cells) from the mouse can be propagated in culture and differentiated into a range of tissues, including neuronal and glial cells. In other studies, more-restricted neural stem cells have been isolated from both the developing and adult rodent brain. Current reports now describe similar pluripotent and neural stem cells cultured from human embryos. While the exact nature of these cells continues to be explored, they can be grown for extended periods of time while retaining the capacity for neuronal and glial differentiation. In some cases, they have been shown to integrate into the developing or damaged adult brain. This article reviews their biology, with a focus on the possible links between ES-cell and neural stem-cell technologies, and the strategies used to isolate and expand defined cell populations.

The final step of pantothenate biosynthesis in higher plants: cloning and characterization of pantothenate synthetase from Lotus japonicus and Oryza sativum (rice)

We have isolated a Lotus japonicus cDNA for pantothenate (vitamin B(5)) synthetase (PS) by functional complementation of an Escherichia coli panC mutant (AT1371). A rice (Oryza sativum) expressed sequence tag, identified by sequence similarity to PS, was also able to complement the E. coli auxotroph, as was an open reading frame from Saccharomyces cerevisiae (baker's yeast). The Lotus and rice cDNAs encode proteins of approx. 34 kDa, which are 65% similar at the amino acid level and do not appear to encode N-terminal extensions by comparison with PS sequences from other organisms. Furthermore, analysis of genomic sequence flanking the coding sequence for PS in Lotus suggests the original cDNA is full-length. The Lotus and rice PSs are therefore likely to be cytosolic. Southern analysis of Lotus genomic DNA indicates that there is a single gene for PS. Recombinant PS from Lotus, overexpressed in E. coli AT1371, is a dimer. The enzyme requires d-pantoate, beta-alanine and ATP for activity and has a higher affinity for pantoate (K(m) 45 microM) than for beta-alanine (K(m) 990 microM). Uncompetitive substrate inhibition becomes significant at pantoate concentrations above 1 mM. The enzyme displays optimal activity at about 0.5 mM pantoate (k(cat) 0.63 s(-1)) and at pH 7.8. Neither oxopantoate nor pantoyl-lactone can replace pantoate as substrate. Antibodies raised against recombinant PS detected a band of 34 kDa in Western blots of Lotus proteins from both roots and leaves. The implications of these findings for pantothenate biosynthesis in plants are discussed.

Response to cladribine in previously treated patients with chronic lymphocytic leukaemia identified by ex vivo assessment of drug sensitivity by DiSC assay

The ability to identify non-responders to cytotoxic chemotherapy has significant clinical and economic benefits. Differential staining cytotoxicity (DiSC) assays were performed in 34 previously treated patients with chronic lymphocytic leukaemia prior to treatment with cladribine. Of the 28 identified as ex vivo sensitive, 26 achieved a complete (CR) or partial response (PR) (median length of response 1. 5 years, median survival 3.37 years) and two had a >70% fall in lymphocytes: six identified as ex vivo resistant failed to respond. The DiSC assay can accurately identify a subgroup of patients resistant to cladribine.

Multiple basal cell carcinomas in a patient with acute myeloid leukaemia and chronic lymphocytic leukaemia

Skin cancer is a well-recognized risk of prolonged immunosuppression, for example, following renal transplantation. These tumours contrast with idiopathic lesions in that squamous cell, rather than basal cell carcinomas usually predominate. We report a Caucasian female who developed multiple basal cell carcinomas following protracted cytotoxic therapy for acute myeloid leukaemia and subsequently chronic lymphocytic leukaemia. No other clinical risk factors nor relevant polymorphisms of genes encoding for detoxifying enzymes were identified. Immune suppression is a well-recognized cause of multiple skin tumours, the most striking increase usually being of squamous cell carcinomas. We believe this woman is representative of a subgroup of immunosuppressed patients who, for as yet poorly understood reasons, have a predisposition to basal cell, rather than squamous cell carcinoma accrual.

Association of NAD(P)H:quinone oxidoreductase (NQO1) null with numbers of basal cell carcinomas: use of a multivariate model to rank the relative importance of this polymorphism and those at other relevant loci

Glutathione S-transferase GSTM1 B and GSTT1 null, and cytochrome P450 CYP2D6 EM have been associated with cutaneous basal cell carcinoma (BCC) numbers, although their quantitative effects show that predisposition to many BCC is determined by an unknown number of further loci. We speculate that other loci that determine response to oxidative stress, such as NAD(H):quinone oxidoreductase (NQO1) are candidates. Accordingly, we assessed the association between NQO1 null and BCC numbers primarily to rank NQO1 null in a model that included genotypes already associated with BCC numbers. We found that only 14 out of 457 cases (3.1%) were NQO1 null. This frequency did not increase in cases with characteristics linked with BCC numbers including gender, skin type, a truncal lesion or more than one new BCC at any presentation (MPP). However, the mean number of BCC in NQO1*0 homozygotes was greater than in wild-type allele homozygotes and heterozygotes, although the difference was not quite significant (P = 0.06). These data reflect the link between NQO1 null and BCC numbers in the 42 MPP cases rather than the whole case group. We identified an interaction between NQO1 null and GSTT1 null that was associated with more BCC (P = 0.04), although only four cases had this combination. The relative influence of NQO1 null was studied in a multivariate model that included: (i) 241 patients in whom GSTM1 B, GSTT1 null and CYP2D6 EM genotype data were available, and (ii) 101 patients in whom these genotypes, as well as data on GSTM3, CYP1A1 and melanocyte-stimulating hormone receptor (MC1R) genotypes were available. NQO1 null (P = 0.001) and MC1R asp294/asp294 (P = 0.03) were linked with BCC numbers, and the association with CYP2D6 EM approached significance (P = 0.08). In a stepwise regression model only these genotypes were significantly associated with BCC numbers with NQO1 null being the most powerful predictor.