Universal newborn screening: A roadmap for action.

Newborn screening (NBS) prevents morbidity and mortality by screening babies for selected disorders in the first days of life so that early diagnosis and treatment can be initiated. Congenital disorders impact an estimated 8 million or 6% of annual births worldwide, and of the top five that contribute 25% to the global burden of these disorders, three can be identified and managed by NBS. There are determined pockets of activity in Latin America, Sub-Saharan Africa, and the Asia Pacific region, where partnerships among government, non-governmental organizations, academia, the private sector and civil society are developing novel NBS programs that are both saving lives and preventing disability in those who survive.

Exploring individual differences in task switching: Persistence and other personality traits related to anterior cingulate cortex function.

Anterior cingulate cortex (ACC) is involved in cognitive control and decision-making but its precise function is still highly debated. Based on evidence from lesion, neurophysiological, and neuroimaging studies, we have recently proposed a critical role for ACC in motivating extended behaviors according to learned task values (Holroyd and Yeung, 2012). Computational simulations based on this theory suggest a hierarchical mechanism in which a caudal division of ACC selects and applies control over task execution, and a rostral division of ACC facilitates switches between tasks according to a higher task strategy (Holroyd and McClure, 2015). This theoretical framework suggests that ACC may contribute to personality traits related to persistence and reward sensitivity (Holroyd and Umemoto, 2016). To explore this possibility, we carried out a voluntary task switching experiment in which on each trial participants freely chose one of two tasks to perform, under the condition that they try to select the tasks "at random" and equally often. The participants also completed several questionnaires that assessed personality trait related to persistence, apathy, anhedonia, and rumination, in addition to the Big 5 personality inventory. Among other findings, we observed greater compliance with task instructions by persistent individuals, as manifested by a greater facility with switching between tasks, which is suggestive of increased engagement of rostral ACC.

Analysis system of submicron particle tracks in the fine-grained nuclear emulsion by a combination of hard x-ray and optical microscopy.

Analyses of nuclear emulsion detectors that can detect and identify charged particles or radiation as tracks have typically utilized optical microscope systems because the targets have lengths from several µm to more than 1000 µm. For recent new nuclear emulsion detectors that can detect tracks of submicron length or less, the current readout systems are insufficient due to their poor resolution. In this study, we developed a new system and method using an optical microscope system for rough candidate selection and the hard X-ray microscope system at SPring-8 for high-precision analysis with a resolution of better than 70 nm resolution. Furthermore, we demonstrated the analysis of submicron-length tracks with a matching efficiency of more than 99% and position accuracy of better than 5 µm. This system is now running semi-automatically.

Effects of bile acids on 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine-induced aberrant crypt foci and DNA adduct formation in the rat colon.

The effects of deoxycholic acid (DCA) and ursodeoxycholic acid (UDCA) on 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-induced aberrant crypt foci (ACF) in the rat colon were examined. The effect of these bile acids on DNA adduct formation by PhIP in the colon was then analyzed, since the main action of PhIP is the formation of DNA adducts and subsequent gene mutations. For the ACF study, male F344 rats were administered PhIP-HCl (75 mg/kg, 10 doses) by gavage, and a diet containing bile acid (0.4% DCA or UDCA) was provided from 3 days before the first dose of PhIP for 8 weeks. The mean number of ACF per colon of DCA, UDCA and controls were 9.9, 2.4 and 5.5, respectively. The ACF number was significantly increased by DCA and decreased by UDCA (P<0.001). To examine the effect of bile acids on DNA adduct formation, male F344 rats were fed a diet supplemented with bile acids (0.1 or 0.4% of DCA and UDCA) 7 days prior to the PhIP administration. All rats were administered a single dose of PhIP-HCl (50 mg/kg) by gavage and sacrificed 48 hours later. DNA adduct levels of the 0.1% UDCA, 0.1% DCA and controls were 2.93 (adducts/10(7) nucleotides), 2.65 and 1.10, respectively. Those of 0.4% UDCA, 0.4% DCA and controls were 1.64, 1.30 and 1.00, respectively. The PhIP-DNA adduct level was significantly increased by administration of 0.1% UDCA, 0.1% DCA (P<0.05) and 0.4% UDCA (P<0.01). The increasing effect of both DCA and UDCA on PhIP-induced DNA adduct formation was unexpected, and was not directly associated with ACF formation.

Identification and quantification of tamoxifen-DNA adducts in the liver of rats and mice.

A new HPLC gradient system was developed for (32)P-postlabeling analysis to identify and quantify hepatic tamoxifen-DNA adducts of rats and mice treated with tamoxifen. Four stereoisomers of alpha-(N(2)-deoxyguanosinyl)tamoxifen (dG(3')(P)-N(2)-TAM), alpha-(N(2)-deoxyguanosinyl)-N-desmethyltamoxifen (dG(3')(P)-N(2)-N-desmethyl-TAM), and alpha-(N(2)-deoxyguanosinyl)tamoxifen N-oxide (dG(3')(P)-N(2)-TAM N-oxide) were prepared by reacting either alpha-acetoxytamoxifen, alpha-acetoxy-N-desmethyltamoxifen or alpha-acetoxytamoxifen N-oxide with 2'-deoxyguanosine 3'-monophosphate, and used as standard markers for (32)P-postlabeling/HPLC analysis. Our HPLC gradient system can separate the above 12 nucleotide isomers as nine peaks; six peaks representing two each trans epimers (fr-1 and fr-2) of dG(3')(P)-N(2)-TAM, dG(3')(P)-N(2)-N-desmethyl-TAM and dG(3')(P)-N(2)-TAM N-oxide, and three peaks representing a mixture of two cis epimers (fr-3 and fr-4) of nucleotides. Tamoxifen was given to female F344 rats and DBA/2 mice by gavage at doses of 45 mg/kg/day and 120 mg/kg/day, respectively, for 7 days. Totally 15 and 17 tamoxifen-DNA adducts were detected in rats and mice, respectively; among them 13 adducts were observed in both rats and mice. trans-dG-N(2)-TAM (fr-2) and trans-dG(3')(P)-N(2)-N-desmethyl-TAM (fr-2) were two major adducts in both animals. Except for these two adducts, trans-dG-N(2)-TAM N-oxide (fr-2) was the third abundant adduct that accounted for 6.4% of the total adducts in mice, while this accounted for only 0.3% in rats. A trans-isomer (fr-1) and cis-isomers (fr-3 and -4) of dG(3')(P)-N(2)-TAM, dG(3')(P)-N(2)-N-desmethyl-TAM and dG(3')(P)-N(2)-TAM N-oxide were also detected as minor adducts in both animals except for cis-form of dG-N(2)-TAM N-oxide in rats. Although the administered dose for rats was 2.7-fold less than that for mice, the total adduct level of rats (216 adducts/10(8) nucleotides) were 3.8-fold higher than mice (56.2 adducts/10(8) nucleotides). Thus, these three types of tamoxifen adducts accounted for 95.0 and 92.5% of the total DNA adducts of the rats and mice, respectively. The formation of tamoxifen adducts primarily resulted from alpha-hydroxylation of tamoxifen.

Effect of bile acids on formation of azoxymethane-induced aberrant crypt foci in colostomized F344 rat colon.

The effect of bile acids on the formation of azoxymethane induced aberrant crypt foci (ACF) was investigated using the fecal stream-excluded colons of colostomized F344 rats. The excluded colon was irrigated with saline or bile acids (1 mg/0.5 ml per day, 5 days/week) for 4 weeks. The mean numbers of ACF per colon in rats given cholic acid, deoxycholic acid (DCA), chenodeoxycholic acid (CDCA), lithocholic acid, and ursodeoxycholic acid (UDCA) were 160.8, 118.2, 227.8, 150.7 and 87.3, respectively, while that of the control was 174.0. The number of ACF was significantly larger in CDCA, but smaller in UDCA and DCA-treated rats than the control (P<0.01). DCA did not induce apoptosis in the colon under the present conditions.

DNA adduct formation by 2-amino-3-methylimidazo [4,5-f] quinoline (IQ) in rat colon.

A food-born carcinogen, 2-amino-3-methylimidazo [4,5-f] quinoline (IQ) induces cancer in the rat colon. The mechanism for colonic DNA adduct formation leading to cancer by IQ was studied using a colostomized F344 rat model. In this model, the transverse colon of the rat was colostomized, which produced a fecal stream-positive proximal colon and a negative distal colon were produced. When IQ (50 mg/kg) was administered into the distal colon of the colostomized rats (n = 5), the ratio of the DNA adduct level of the distal colonic mucosa to the paired muscular layer 24 hr after dosage was 2.02, whereas that was 1.51 and 1.37 when IQ was administered into the stomach (n = 6) and the vein (n = 5), respectively. This suggested that luminal exposure of IQ induced DNA adduct formation. Since IQ (an amine form) has no reactivity toward DNA, these findings suggested that IQ was immediately activated in the absorbed mucosal cells and reacted with DNA. However, most of the IQ absorbed was metabolically activated in the liver, distributed by blood circulation, and formed DNA adducts in the colonic mucosa and muscular layer.

Identification of hepatic tamoxifen-DNA adducts in mice: alpha-(N(2)-deoxyguanosinyl)tamoxifen and alpha-(N(2)-deoxyguanosinyl)tamoxifen N-oxide.

Tamoxifen-DNA adducts detected in the liver of mice treated with tamoxifen have not yet been identified. In the present study a new type of tamoxifen-DNA adduct, four stereoisomers of alpha-(N:(2)-deoxyguanosinyl)tamoxifen N:-oxide 3'-monophosphate (dG(3'P)-N:(2)-TAM N:-oxide) were prepared as standard DNA adducts by reacting 2'-deoxyguanosine 3'-monophosphate with trans-alpha-acetoxytamoxifen N:-oxide in addition to four stereoisomers of alpha-(N:(2)-deoxyguano- sinyl)tamoxifen 3'-monophosphate (dG(3'P)-N:(2)-TAM) that was reported previously. Liquid chromatography-electrospray ionization-mass spectrometry of the reaction products gave the most abundant ion at m/z 731 ([M - H](-)), which corresponded to dG(3'P)-N:(2)-TAM N:-oxide. The modified products digested by alkaline phosphatase corresponded to the isomers of dG-N:(2)-TAM N:-oxide whose structures were identified previously by mass spectrometry and nuclear magnetic resonance. Using these standard markers, we analyzed the hepatic DNA adducts of female DBA/2 mice treated with tamoxifen at a dosage of 120 mg/kg/day for 7 days by (32)P-post-labeling coupled with an HPLC/radioactive detector. Mixtures of eight isomers of dG(3'P)-N:(2)-TAM and dG(3'P)-N:(2)-TAM N-oxide were separated into six peaks, since each of the cis epimers were not separated under the present HPLC conditions. Nine adducts were detected in all liver samples of mice. An epimer of trans-dG(3'P)-N:(2)-TAM was detected as the principal DNA adduct at a level of 29.0 adducts/10(8) nucleotides, which accounted for 53.3% of the total tamoxifen-DNA adducts. Lesser amounts of cis-dG(3'P)-N:(2)-TAM (2.8%) were also observed. An epimer of the trans-dG(3'P)-N:(2)-TAM N:-oxide (3.9 adducts/10(8) nucleotides) was detected as the third biggest adduct (7.2% of the total). The cis-dG(3'P)-N:(2)-TAM N:-oxide (0.4 adducts/10(8) nucleotides) accounted for 0.7% of the total. Thus, dG(3'P)-N:(2)-TAM and dG(3'P)-N:(2)-TAM N:-oxide were identified in tamoxifen-treated mouse liver.

Identification of tamoxifen-DNA adducts induced by alpha-acetoxy-N-desmethyltamoxifen.

Treatment with tamoxifen increased the risk of endometrial cancers in breast cancer patients and women participating in the chemoprevention study. In our laboratory, tamoxifen-DNA adducts, including alpha-(N(2)-deoxyguanosinyl)tamoxifen (dG-N(2)-TAM), were detected in the endometrium of women taking tamoxifen [Shibutani, S., et al. (1999) Chem. Res. Toxicol. 12, 646-653]. On the basis of recent animal studies, deoxyguanosinyl-N-desmethyltamoxifen (dG-N-desmethylTAM) adducts are also suspected to be formed in the liver. In the study presented here, we synthesized alpha-acetoxy-N-desmethyltamoxifen as a model activated metabolite of N-desmethyltamoxifen. The overall yield of alpha-acetoxy-N-desmethyltamoxifen from alpha-hydroxytamoxifen was approximately 42%. alpha-Acetoxy-N-desmethyltamoxifen was highly reactive to 2'-deoxyguanosine, as was similarly observed for tamoxifen alpha-sulfate. The two reaction products were identified as a mixture of epimers of the trans form or cis form of alpha-(N(2)-deoxyguanosinyl)-N-desmethyltamoxifen (dG-N(2)-N-desmethylTAM) by mass and proton magnetic resonance spectroscopy. In addition, the trans and cis forms of dG 3'-monophosphate-N(2)-N-desmethylTAM were prepared as standard markers for (32)P-postlabeling/HPLC analysis. Using this technique, dG-N(2)-N-desmethylTAM adducts were detected in calf thymus DNA reacted with alpha-acetoxy-N-desmethyltamoxifen.

Tamoxifen-DNA adducts formed by alpha-acetoxytamoxifen N-oxide.

DNA adduct formation is assumed to be a major carcinogenic event, leading to the development of endometrial cancer in breast cancer patients taking tamoxifen and healthy women enrolled in a tamoxifen chemopreventive trial. To determine whether DNA adducts were formed by tamoxifen, trans- and cis-alpha-acetoxytamoxifen N-oxides were synthesized as model-activated forms via major tamoxifen metabolites, tamoxifen N-oxide and alpha-hydroxytamoxifen N-oxide. When alpha-acetoxytamoxifen N-oxide was reacted with human DNA, at least three DNA adducts were detected by (32)P-postlabeling coupled with HPLC. The total amount of DNA adducts formed by trans-alpha-hydroxytamoxifen N-oxide was 1.5-fold higher than that formed by the cis form. Both trans- and cis-alpha-acetoxytamoxifen N-oxide reacted with 2'-deoxyguanosine, resulting in the formation of three adducts (fr-1, fr-2-1, and fr-2-2). These products were studied using mass spectroscopy and proton magnetic resonance spectroscopy. fr-1 was identified as a mixture of the epimers of trans-alpha-(N(2)-deoxyguanosinyl)tamoxifen N-oxide. fr-2-1 and fr-2-2 were determined to be epimers of cis-alpha-(N(2)-deoxyguanosinyl)tamoxifen N-oxide.

Generation of new transposons in vivo: an evolutionary role for the "staggered" head-to-head dimer and one-ended transposition.

From a plasmid carrying the tnpA gene and one inverted repeat sequence (IR) of transposon Tn3, plasmids containing a structure characteristic of transposons, i.e., two IRs flanking a tnpA gene, were generated spontaneously in vivo. They appear to have arisen either through the formation of a "staggered" head-to-head dimer or by so-called one-ended transposition. These putative transposons could indeed transpose to, or form cointegrates with, a recipient plasmid. Based on these findings it is proposed that a primeval transposase gene and its target site evolved first, and subsequently gave rise to a "fully-fledged" transposon by head-to-head dimerization or one-ended transposition.

The effects of habitat fragmentation on persistence of source-sink metapopulations in systems with predators and prey or apparent competitors.

We consider systems with one predator and one prey, or a common predator and two prey species (apparent competitors) in source and sink habitats. In both models, the predator species is vulnerable to extinction, if productivity in the source is insufficient to rescue demographically deficient sink populations. Conversely, in the model with two prey species, if the source is too rich, one of the prey species may be driven extinct by apparent competition, since the predator can maintain a large population because of the alternative prey. Increasing the rate of predator movement from the source population has opposite effects on prey and predator persistence. High emigration rate exposes the predator population to danger of extinction, reducing the number of individuals that breed and produce offspring in the source habitat. This may promote coexistence of prey by relaxing predation pressure and apparent competition between the two prey species. The number of sinks and spatial arrangement of patches, or connectivity between patches, also influence persistence of the species. More sinks favor the prey and fewer sinks are advantageous to the predator. A linear pattern with the source at one end is profitable for the predator, and a centrifugal pattern in which the source is surrounded by sinks is advantageous to the prey. When the dispersal rate is low, effects of the spatial structure may exceed those of the number of sinks. In brief, productivity in patches and patterns of connectivity between patches differentially influence persistence of populations in different trophic levels.

The molecular basis of the instability of a crp- mutation in Escherichia coli.

We have described a rapid spontaneous conversion in the stationary phase of Escherichia coli strain DOO (crp-) cells as a whole population to crp+ state (Sugino and Morita, 1994). In this paper we have tried to elucidate the molecular basis of this unidirectional conversion by cloning and sequencing of the crp gene in their crp+ and crp- states. We have found that in the original crp- strain, an IS2 element has been inserted between its original promoter and the coding region of the crp gene in the so-called orientation II (Ahmed et al., 1981), accompanied by an 11 bp deletion. Unexpectedly, the crp+ "revertants" derived from the crp- mutant had no difference in sequence from the crp-, either in the coding or the regulatory region. This suggests that a change at another locus, such that this change somehow activates the expression of the crp gene to the level of a normal crp+, is responsible for the apparent reversion from crp- to crp+.

Effects of dietary bile acids on formation of azoxymethane-induced aberrant crypt foci in F344 rats.

The present study has demonstrated the influence of bile acids (BAs) on the development and growth of azoxymethane (AOM)-induced aberrant crypt foci (ACF). Male F344 rats were treated with two doses of AOM (15 mg/kg) at 7 days apart and fed either basal MF or MF plus 0.4% of cholic (CA), deoxycholic (DCA), chenodeoxycholic (CDCA), lithocholic (LCA) and ursodeoxycholic (UDCA) acid mixed diets for 8 weeks after the first AOM dose. The mean number of ACF/colon of the rats fed CA, DCA, CDCA and LCA were higher than that of MF-fed group and the differences were statistically significant (P < 0.005). But the mean number of ACFs/colon was significantly (P < 0.005) lower in UDCA diet-fed rats compared to MF. UDCA-fed rats also showed a significant decrease in average crypt multiplicity (number of crypts/focus) of ACF compared to MF alone. The mean number of ACF with > or =5 crypts was about 2.5-3.7 times higher in case of CA, DCA, CDCA and LCA and about 8.2 times lower in UDCA compared to the control MF diet group. In a parallel study, feeding for 18 weeks of the same BAs mixed diets without AOM administration did not significantly induce ACF. Therefore, these data suggest that dietary BAs by themselves do not induce ACF in F344 rats but enhance or, in the case of UDCA, suppress the development and growth of AOM-induced ACF.

Nested deletions from a fixed site as an aid to nucleotide sequencing: an in vitro system using Tn3 transposase.

We have previously constructed a cloning/sequencing vector, with an in vivo system capable of creating nested deletions from the end of transposon Tn3, which is useful for sequencing large DNAs. Here we report an in vitro system which uses an ammonium sulfate fraction of extract from E. coli cells harboring a Tn3 transposase overproducer plasmid to generate nested deletions. A key feature of the procedure is exhaustive digestion of the reaction products with a restriction enzyme that cleaves only between the Tn3 "right" terminus and the cloned fragment. This step reduces the noise level due to mechanisms other than deletions from the Tn3 terminus, and facilitates detection and isolation of the desired deletion products. This system enables us to save at least 2 days' time when obtaining the necessary deletions compared with the in vivo system.

DNA adduct formation by hormonal steroids in vitro.

We examined the binding of various steroid hormones to DNA in vitro by means of 32P-postlabeling. Seventeen steroid hormones and cholesterol (CS) were incubated with human liver DNA at 37 degrees C for 1 h under aerobic conditions in the absence of catalysis. The reaction mixtures were analyzed by the nuclease P-1 version of 32P-postlabeling. The results showed that cortexolone (CX), prednisolone (PS), cortisone (CN), cortisol (CL), tetrahydrocortisol (TC), corticosterone (CC), 11-deoxycorticosterone (DC), dexamethasone (DX), dihydrocortisol (DL), and aldosterone (AL) covalently bound with DNA. However, progesterone (PG), 17 alpha-hydroxyprogesterone (HG), estrone (E1), estradiol (E2), estriol (E3), testosterone (TS), cortol (CR) and the original compound for biosynthesis, CS, did not form adducts. In absence of DNA, the steroids themselves did not give rise to any spot on TLC under the same conditions. The dose-responses of DNA binding by DC, DL, CC, CL and CN were linear. The relative adduct labeling of reactive steroids at a concentration of 2 mM were as follows: 68.8 (CX), 53.2 (PS), 39.6 (CN), 29.9 (CL), 20.9 (TC), 12.9 (CC), 12.3 (DC), 7.5 (DX), 4.7 (DL), 1.2 (AL) adducts per 10(8) nucleotides. Reactive and nonreactive steroids were distinguishable by the presence or absence of the carbonyl group (-CO-CH2OH) at carbon seventeen (C17) of the cholesterol skeleton. This implies that the electrophilic carbonyl or a neighboring group perhaps involved in the formation of covalent bond with DNA. To investigate the nature of target base(s) of these DNA reactive steroids, mononucleotides of all four bases of DNA were reacted with CN, CL, CC and cochromatographed with the obtained spots of DNA reactions. The results of which stated that these steroids and guanine reaction gave the same spots as observed in DNA reaction, indicating guanine is the main target of these DNA reactive steroids. Hep G2 human hepatocellular carcinoma cells were used as an alternative model. Although nine steroids (CL, DL, TC, PS, DX, PG, E2, TX, CR) did not react with intracellular DNA under our experimental conditions, our findings suggested that some hormonal steroids can form covalent DNA adducts in vivo.

The effect of the crp genotypes on the transformation efficiency in Escherichia coli.

We have found that a significant difference exists in transformation efficiency between the crp+/crp- isogenic pair of strains of Escherichia coli, with the efficiency being much higher in crp- than in crp+. The ratio of transformation efficiency between crp+ and crp- strains depends very little on the plasmid size. This observation suggests that the difference of the transformation efficiency is due to mechanisms other than a crp-regulated endonuclease. The crp gene is one of the first specific genes that have been shown to affect transformation efficiency.

Mucosa-preferential DNA adduct formation by 2-amino-3-methylimidazo-[4,5-f]quinoline in the rat colonic wall.

The mechanism of mucosa-specific formation of DNA adducts, which was found recently in human intestines, was studied in male F344 rats treated with 2-amino-3-methylimidazo[4,5-f]quinoline (IQ). There are three conceivable pathways for p.o. administered IQ to reach the target colonic mucosal cells: pathway 1, through the digestive canal which exposes from the lumenal direction; pathway 2, following enterohepatic circulation re-expose from the lumenal direction; and pathway 3, exposure via blood circulation. To investigate these possible pathways, the following surgical procedures were performed: (a) portal catheterization for IQ administration to eliminate pathway 1 and (b) choledochal catheterization for bile drainage to eliminate pathway 2. When both procedures are combined, only pathway 3 is active. Four types of IQ-DNA adducts were commonly observed in the colons of all experimental groups, with no qualitative difference between the mucosal and muscular layers. When IQ-HCl was administered by p.o. gavage at a dose of 100 mumol/kg body weight, approximately 70% of the IQ-DNA adducts in the colonic mucosa (13.1 +/- 4.3 adducts/10(7) nucleotides) was induced through pathway 1. Pathway 3 induced the remaining 30% of mucosal adducts, producing equal adduct levels in both layers. Pathway 2 did not work for adduct formation. The DNA adduct formation was unaffected in the presence of intestinal flora, indicating that detoxified IQ does not reactivate by floral enzymes. In conclusion, mucosa-specific DNA adduct formation in the colon is caused most likely by the absorption of carcinogens through the lumen.

Mucosa-specific DNA adducts in human small intestine: a comparison with the colon.

The presence of several covalent DNA adducts in the human colon was demonstrated by 32P-postlabeling in a previous study. We demonstrated that DNA of all the colonic mucosa tested were selectively adducted by a single genotoxic agent and this modification was completely absent in the DNA of muscular layers. In this study, the DNA adducts of the small intestine are compared with those of the colon to understand the role of mucosa-specific DNA adduct (MSA) in intestinal carcinogenesis. The mucosal DNA of the small intestine from 19 adults undergoing surgery due to gastric carcinoma (seven cases), pancreatic carcinoma (four cases), colon carcinoma (four cases), small intestinal tumor (two cases), intestinal trauma (one case) and ectopic pancreas (one cases) were analyzed. The mucosa-adjacent muscular layer DNA of the corresponding samples was examined as a control. Several common DNA adducts were observed in both mucosal and muscular layers of all the adults. Besides these common background DNA adducts, two MSAs (Si1, Si2) were detected in most of the adults as in colon cases. Si1 was present in all adults examined (19/19 cases) at a level of 0.04-0.22 adducts/10(8) nucleotides (average 0.09) and Si2 was found in 13/19 patients at a level of 0.03-0.08 adducts/10(8) nucleotides (average 0.05). Si2 was the same adduct detected in the adult colonic mucosa. However, they were absent in the adjacent muscular layer as well as in the neonatal intestine tested as a control. The total level of the mucosa-specific DNA adducts of the small intestine was approximately 28-fold lower than that of the colon. Considering that the incidence of cancer in the small intestine is rather lower than that in the colon, these results may be relevant to the development of human intestinal cancer.