The possible mutagenic potential of exposure to 1.5 GHz electromagnetic near field (EMF) was investigated using brain tissues of Big Blue mice (BBM). Male BBM were locally exposed to EMF in the head region at 2.0, 0.67, and 0 W/kg specific absorption rate for 90 min/day, 5 days/week, for 4 weeks. No gliosis or degenerative lesions were histopathologically noted in brain tissues, and no obvious differences in Ki-67 labeling and apoptotic indices of glial cells were evident among the groups. There was no significant variation in the frequency of independent mutations of the lacI transgene in the brains. G:C to A:T transitions at CpG sites constituted the most prevalent mutations in all groups and at all time points. Deletion mutations were slightly increased in both the high and low EMF exposure groups as compared with the sham-exposed group, but the differences were not statistically significant. These findings suggest that exposure to 1.5 GHz EMF is not mutagenic to mouse brain cells and does not create any increased hazard with regard to brain tumor development.

The use of cellular phones has dramatically increased throughout the world during the past 10 years. In Japan, a digital cellular system operating at 800 MHz (PDC4-800) started service in 1993, followed by a 1.5 GHz system (PDC-1500) in 1994. By the end of 2000, the number of subscribers to cellular phone services had grown to 61 million in Japan. This is equivalent to ∼50% of the total Japanese population.5 Because exposure to EMF from a cellular phone is concentrated at the head, which is in close proximity to the antenna, the potential hazard risk to human health with EMF, especially for brain tumors, leukemia, and salivary gland neoplasia, has been a source of great concern.

We have already reported that 929 MHz or 1.5 GHz EMF exposure does not promote liver carcinogenesis in rats (1, 2) or skin carcinogenesis in mice (3). In the present study, we have focused on the genotoxic effects of EMFs on the brain. To investigate whether mutations are caused in brain DNA by EMF exposure and, if so, to examine the kind of mutations that are induced, we used mice that are transgenic for the lacI marker gene in λ phage (BBM). These mice are known to provide a powerful in vivo mutagenesis assay system (4).

Animals.

Male BBM with a C57BL/6 genetic background (heterozygous) were obtained at 5 weeks of age from Stratagene (La Jolla, CA). They were housed three to a plastic cage with hardwood chips for bedding and fed a standard diet (Oriental MF; Oriental Yeast Co. Ltd., Tokyo, Japan) and water ad libitum. The animals were kept in an environmentally controlled room maintained at a temperature of 22 ± 2°C, a relative humidity of 55 ± 10%, and a 12-h light/dark cycle. They were acclimatized for 1 week before use.

Exposure Apparatus and EMF Dosimetry.

The exposure apparatus was specially designed for this study. Fig. 1 shows a diagram of the exposure apparatus used in the present study. The signal generator produced a 1.5 GHz Time Division Multiple Access signal that is presently used in the Japanese PDC system. The signal was amplified and then split to individual exposure boxes, made of aluminum, with all of the insides, except for the left-side face and roof, covered with planar rubber ferrite absorber having a thickness of 7 mm and a reflection loss of at least 21.8 dB. The roof of the box was a transparent absorber with a thickness of 22.5 mm and was able to supply a reflection loss of 20 dB. The left-side face of the box acted as the ground for a monopole antenna, which had a horizontal arrangement. Each mouse was constrained with an acrylic holder so that its head was just 4 mm beneath the antenna element. For realizing localized exposure to the whole mouse brain, a flexible magnetic sheet with a thickness of 1 mm was used to cover the low part of the acrylic holder, acting as a shielding material to suppress the SAR in the lower part of the mouse body. As a result, with an antenna output of 57 mW, the exposure system could provide a brain-average SAR of 2 W/kg and a whole-body-averaged SAR of 0.27 W/kg. The low value excluded the possibility of thermal stress. The results of computer simulation demonstrated that the field strength of EMF exposure in the whole brain was not uniform but varied within 10%.

Experimental Design.

The experimental protocol in the present study was approved by the Animal Care Committee of Nagoya City University Medical School. BBM received EMF exposure at 2.0, 0.67, and 0 W/kg SAR for 90 min/day, 5 days/week, for 4 weeks. BBM in the sham group were also constrained with an acrylic holder in the same manner as those in the EMF exposure groups, except without actual exposure to EMF. Five animals each were killed at 2 and 4 weeks after the start of the experiment, and the brains were removed. Four transverse slices of the right cerebral hemisphere from the frontal to occipital lobe and two transverse slices of the right cerebellar hemisphere were cut, fixed in formalin, and processed sequentially. Remaining tissues were immediately frozen in liquid nitrogen and stored at −80°C until processing. Four μm-thick sections through all slices were cut and stained with H&E for histological examination.

Mutation Assay.

DNA was extracted from the brain of each mouse by the phenol/chloroform method. In vitro λ packaging and mutation assays were performed as recommended by Stratagene. MnF was calculated by dividing the number of independent mutations by the total number of plaques analyzed.

DNA Sequencing Analysis of lacI Mutations.

Mutant lacI genes were recovered in the pBluescript phagemid, using a Rapid Excision kit (Stratagene). The excised phagemid was purified with a MiniPrep kit (Qiagen, Chatsworth, CA). Mutations in the lacI gene were identified after PCR using an ABI PRISM BigDye terminator cycle sequencing FS ready reaction kit (Perkin-Elmer Applied Biosystems, Foster City, CA). PCR was performed with 25 cycles of denaturing (96°C) for 30 s, annealing (50°C) for 15 s, and extension (60°C) for 4 min. Primers for DNA sequencing were 5′-GACACCATCGAATGGTGCAA-3′ (1F), 5′-AAGCGGCGGTGCACAATCTT-3′ (2F), 5′-CACTGCGATGCTGGTTGCC-3′ (3F), 5′-CCCGCCAGTTGTTGTGCCAC-3′ (4R), and 5′-TTTCACATTCACCACCCTGA-5′ (5R) synthesized by Nihon Gene Research Laboratories (Sendai, Japan). PCR products were sequenced with an ABI PRISM 310 genetic analyzer (Perkin-Elmer Applied Biosystems).

Immunohistochemistry.

Brain sections were treated with anti-Ki-67 antibody (Novocastra Laboratories Ltd., Newcastle, United Kingdom) and then sequentially with secondary antibody and avidin-biotin complex reaction (Vectastain ABC elite kit; Vector Laboratories Inc., Burlingame, CA). The sites of peroxidase binding were demonstrated with diaminobenzidine as the substrate. For analysis of apoptosis, sections were treated using the terminal deoxynucleotidyltransferase-mediated nick end labeling method (ApopTag apoptosis detection kit; Intergen, Purchase, NY). Sections were then counterstained with hematoxylin for microscopic examination. Labeling indices for cell proliferation and apoptosis were generated by counting >2000 glial cells in both cortex and medulla of the frontal, parietal, and temporal lobes of cerebrum, as well as basal ganglia and hippocampus under a microscope at high magnification, and were expressed as percentages of positive cells.

Statistical Analyses.

The level of significance of the differences in MnF values between the groups was analyzed using Fisher’s exact probability test.

Body and Brain Weights.

Data for final body and brain weights are summarized in Table 1. No differences were evident among the three groups.

MnFs in the Brain.

MF was calculated as the number of mutant blue plaques/106 plaques, and the MnF was calculated as the number of independent mutants/106 plaques. lacI mutants from the high EMF (n = 59), low EMF (n = 85), and sham (n = 55) groups were subjected to sequencing analysis. After excluding mutations of a clonal origin, 55, 49, and 47 independent mutations, respectively, were identified. One mutant from the sham mouse failed to demonstrate any mutation in lacI and its promoter sequence.

lacI MF in brains at both weeks 2 and 4 and MnF in group 2 (low EMF exposure) at week 4 tended to be increased as compared with the sham group, but differences were not statistically significant. Furthermore, no significant differences in MF and MnF between high EMF exposure and sham group were observed, although lacI mutants and mutations in high EMF exposure groups were also slightly increased at week 4 (Table 2).

Mutation Spectra of the Mutant lacI Gene.

Among the mutations detected, base substitutions accounted for >75%, and G:C to A:T transitions at CpG sites, indicative of spontaneous mutations, were the most common type in all groups and at any time point (Table 3). There were no differences in lacI mutation spectra among the groups, the findings corresponding with those expected from the Big Blue lacI database.6 There were no obvious hotspots for mutations in EMF-exposed mice (Table 4). Deletion mutations were slightly increased in both high and low EMF-exposed mice compared with the sham group, but this was not significant.

Histopathological and Immunohistochemical Analysis for Cell Proliferation and Apoptosis.

No histopathological changes, such as gliosis or degenerative lesions, were noted in brain tissues. There was no obvious difference in Ki-67 labeling and apoptotic indices of cerebral glial cells among the groups at either weeks 2 or 4 (Table 1).

The transgenic rodent mutation assay systems based on the lac operon genes, BBM and Muta mice, provide versatile and sensitive in vivo mutagenicity models in the genetic toxicology field. Earlier reports demonstrated that an increase in MF was evident in brains of Muta mice exposed to whole body X-ray irradiation (5) but not apparent in those treated with alkylating agents such as ethylnitrosourea and propylnitrosourea (6, 7). The existence of the blood brain barrier may be the reason for the negative results in the latter studies. In the present study, a lack of any direct effects with 1.5 GHz EMF exposure, not only in terms of brain DNA damage but also proliferation of glial cells, was observed in BBMs. The finding of no increase in DNA mutations in brain cells is in line with previous reports (8, 9), and the values for MF and MnF in the sham-treated mice were almost the same as the spontaneous mutation data reported earlier (10). These results suggest that there were no technical errors in detection of lacI mutants, and there were no effects attributable to stress from constraint in acrylic holders on DNA damage in brain cells.

Temperature rise in tissue is known to induce increased DNA synthesis in cultured cells (11, 12) and to act as a cofactor of carcinogenesis (13). However, the maximum temperature rise in the human brain attributable to exposure to EMF from cellular phones has been calculated to be 0.1°C (14, 15). The thermal effects from EMF by cellular phone use, therefore, would be expected to be negligible in the human situation. The exposure apparatus used in this study was in fact specially designed to exclude thermal effects of EMF on the brain, and we speculated from the data for brain weights in EMF-exposed mice that thermal stress was virtually absent.

It is widely accepted that multiple genetic alterations occur stepwise in the process of tumor development. With human gliomas, a major type of primary brain tumor, p53 gene mutations have been reported as an early event in tumorigenesis (16). Regarding changes in the cell cycle arrest pathway, retinoblastoma gene mutations were found in up to 25% of high-grade astrocytomas, and the INK4A gene is deleted homozygously in the majority of glioblastomas (16). These findings suggest that DNA damage in a variety of critical genes plays an important role in brain tumor development. From the present evidence, therefore, the possibility that, in Japan, EMF exposure from cellular phone use can directly provoke the development of brain tumors is not great.

The present experiment was limited to only 4 weeks and does not directly reflect the human situation because cellular phones are often used much longer in daily life. However, the 4-week experimental duration was sufficient because we focused on whether EMF exposure can cause mutations in brain DNA in vivo and whether EMF exposure possesses initiating activities on brain carcinogenesis. The manifestation time for fixing mutations is varied among tissues, depending on their proliferation activity. A sampling time of 4 weeks is generally recommended to examine the genotoxic effects in lower proliferating tissues such as brain (17). Regarding the effects of 1.5 GHz EMF near field exposure on brain tumor development, a long-term experiment using rats is in progress in our laboratory.

Several epidemiological studies investigating the relationship between cellular phone use and cancer development have demonstrated no supportive evidence for any association with tumors of the brain or salivary gland, as well as leukemia (18, 19, 20, 21). In one animal study, lymphoma development was increased after whole-body 900 MHz EMF far field exposure in Eμ-Pim1 transgenic mice for 60 min/day for 18 months (22). However, studies using F344 rats involving 836 MHz EMF exposure to the head for 2 h/day, 4 days/week for 2 years demonstrated no effects of either analogue or digitally encoded signals on the development of brain tumors (23, 24). Thus, both epidemiological and animal experimental data suggest that EMF exposure attributable to cellular phone use is not associated with any elevated risk of brain tumor development. The present data also support this conclusion.

Fig. 1.

Schematic illustration of the exposure apparatus.

Fig. 1.

Schematic illustration of the exposure apparatus.

Close modal

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

1

This work was supported by a grant from the Association of Radio Industries and Business (ARIB), Japan.

4

The abbreviations used are: PDC, personal digital cellular; EMF, electromagnetic near field; BBM, Big Blue mice; SAR, specific absorption rate; MnF, mutation frequency; MF, mutant frequency.

5

Internet address: http://www.home.soumu.go.jp/hakusho/tsushin/h13/index.htm.

6

Internet address: http://eden.ceh.uvic.ca/cgi-win/laci1.exe.

Table 1

Body, brain weights, and Ki-67 and apoptotic indices in brains of BBM treated with EMF

EMF exposure (W/kg SAR)No. of miceBody weight (g)Brain weight (g)Ki-67 labeling index (%)Apoptotic index (%)
Week 2      
2.00 21.1 ± 1.8 0.42 ± 0.01 0.18 ± 0.08 
0.67 23.1 ± 1.2 0.41 ± 0.01 0.18 ± 0.05 0.01 ± 0.02 
22.5 ± 0.3 0.43 ± 0.01 0.21 ± 0.09 
Week 4      
2.00 21.4 ± 0.6 0.41 ± 0.01 0.17 ± 0.08 0.01 ± 0.02 
0.67 21.7 ± 0.6 0.41 ± 0.01 0.28 ± 0.13 0.01 ± 0.02 
22.5 ± 0.8 0.40 ± 0.02 0.20 ± 0.11 
EMF exposure (W/kg SAR)No. of miceBody weight (g)Brain weight (g)Ki-67 labeling index (%)Apoptotic index (%)
Week 2      
2.00 21.1 ± 1.8 0.42 ± 0.01 0.18 ± 0.08 
0.67 23.1 ± 1.2 0.41 ± 0.01 0.18 ± 0.05 0.01 ± 0.02 
22.5 ± 0.3 0.43 ± 0.01 0.21 ± 0.09 
Week 4      
2.00 21.4 ± 0.6 0.41 ± 0.01 0.17 ± 0.08 0.01 ± 0.02 
0.67 21.7 ± 0.6 0.41 ± 0.01 0.28 ± 0.13 0.01 ± 0.02 
22.5 ± 0.8 0.40 ± 0.02 0.20 ± 0.11 
Table 2

Data for lacI mutation frequency (MnF) in brains of BBM treated with EMF

Treatment/experimental weekSample no.Total plaquesMutantsMutationsMnF (×10−6)
High EMF/2 week 101 223,000  
 102 268,000  
 103 219,000  
 104 196,000  
 105 205,000  
Total  1,111,000 23 23 20.7 
High EMF/4 week 106 457,000  
 107 275,000  
 108 536,000  
 109 407,000  
 110 311,000 13 11  
Total  1,986,000 36 32 16.1 
Low EMF/2 week 201 217,000  
 202 210,000 23  
 203 225,000  
 204 210,000  
 205 243,000  
Total  1,105,000 38 18 16.3 
Low EMF/4 week 206 302,000 15  
 207 337,000  
 208 381,000  
 209 361,000  
 210 330,000  
Total  1,711,000 48 31 18.1 
Sham/2 week 301 255,000  
 302 208,000  
 303 201,000  
 304 180,000  
 305 216,000  
Total  1,060,000 23 22 20.8 
Sham/4 week 306 349,000  
 307 416,000  
 308 395,000 10  
 309 520,000  
 310 309,000  
Total  1,989,000 31 25 12.6 
Treatment/experimental weekSample no.Total plaquesMutantsMutationsMnF (×10−6)
High EMF/2 week 101 223,000  
 102 268,000  
 103 219,000  
 104 196,000  
 105 205,000  
Total  1,111,000 23 23 20.7 
High EMF/4 week 106 457,000  
 107 275,000  
 108 536,000  
 109 407,000  
 110 311,000 13 11  
Total  1,986,000 36 32 16.1 
Low EMF/2 week 201 217,000  
 202 210,000 23  
 203 225,000  
 204 210,000  
 205 243,000  
Total  1,105,000 38 18 16.3 
Low EMF/4 week 206 302,000 15  
 207 337,000  
 208 381,000  
 209 361,000  
 210 330,000  
Total  1,711,000 48 31 18.1 
Sham/2 week 301 255,000  
 302 208,000  
 303 201,000  
 304 180,000  
 305 216,000  
Total  1,060,000 23 22 20.8 
Sham/4 week 306 349,000  
 307 416,000  
 308 395,000 10  
 309 520,000  
 310 309,000  
Total  1,989,000 31 25 12.6 
Table 3

Types of lacI gene mutations observed in the brains of BBM

Mutation classNo. of mutations (%)
High EMFLow EMFSham
2 wk4 wkTotal2 wk4 wkTotal2 wk4 wkTotal
Base substitution          
 A:T to G:C 1 (2) 2 (4) 
 A:T to C:G 3 (5) 4 (8) 
 A:T to T:A 1 (2) 1 (2) 1 (2) 
 G:C to A:T 13 13 26 (47) 10 15 25 (51) 17 13 30 (64) 
 [at CpG] [8] [8] [16] [8] [11] [19] [14] [13] [27] 
 G:C to T:A 13 (24) 9 (18) 9 (19) 
 G:C to C:G 3 (5) 2 (4) 3 (6) 
Deletion          
 A:T 3 (6) 
 G:C 5 (9) 1 (2) 2 (4) 
 More than 2 bases 3 (5) 2 (4) 
Insertion          
 A:T 
 G:C 
 More than 2 bases 2 (4) 
Total 23 32 55 (100) 18 31 49 (100) 22 25 47 (100) 
Mutation classNo. of mutations (%)
High EMFLow EMFSham
2 wk4 wkTotal2 wk4 wkTotal2 wk4 wkTotal
Base substitution          
 A:T to G:C 1 (2) 2 (4) 
 A:T to C:G 3 (5) 4 (8) 
 A:T to T:A 1 (2) 1 (2) 1 (2) 
 G:C to A:T 13 13 26 (47) 10 15 25 (51) 17 13 30 (64) 
 [at CpG] [8] [8] [16] [8] [11] [19] [14] [13] [27] 
 G:C to T:A 13 (24) 9 (18) 9 (19) 
 G:C to C:G 3 (5) 2 (4) 3 (6) 
Deletion          
 A:T 3 (6) 
 G:C 5 (9) 1 (2) 2 (4) 
 More than 2 bases 3 (5) 2 (4) 
Insertion          
 A:T 
 G:C 
 More than 2 bases 2 (4) 
Total 23 32 55 (100) 18 31 49 (100) 22 25 47 (100) 
Table 4

List of the lacI gene mutations observed in the brains of BBM

Nucleotide no.Codon no.MutationAmino acid changeNo. of mutations
TypeaWild typeDetectedHigh EMFLow EMFSham
42 ACATThr→Met  
49 TAC TAA Tyr→Stop  
53 GTC TTC Val→Phe   
56 10 GCA ACA Ala→Thr 
56 10 GCA CCA Ala→Pro   
69 14 GGGTGly→Val   
78 17 TATGTyr→Cys   
82 18 CAG CAC Gln→His   
86 20 GTT TTT Val→Phe  
92 22 CGC TGC Arg→Cys 
93 22 CGCTArg→Leu   
93 22 CGCAArg→His   
95 23 GTG ATG Val→Met  
95 23 GTG TTG Val→Leu   
116 30 GTT TTT Val→Phe   
117 30 GTGGVal→Gly   
117 30 GTGAVal→Asp   
135 36 GAGA Frameshift (−1)   
140 38 GTG ATG Val→Met   
150 41 GCGAAla→Glu   
158 44 GAG TAG Glu→Stop   
174 49 CCCAPro→His   
178 50 AAC AAA Asn→Lys   
179 51 CGC TGC Arg→Cys 
180 51 CGCAArg→His 
185 53 GCA TCA Ala→Ser   
185 53 GCA ACA Ala→Thr  
186 53 GCGTAla→Val   
190 54 CAA CAT Gln→His   
191 55 CAA TAA Gln→Stop  
198 57 GCGTAla→Val 
201 58 GGGTGly→Val   
206 60 CAG TAG Gln→Stop   
215 63 TTGCTG TTGCTGATTGGCTG Frameshift (+8)   
219 64 ATAGIle→Ser   
224 66 GTT TT Frameshift (−1)   
228 67 GCGAAla→Asp   
236 70 AGT TGT Ser→Cys   
270 81 GCGTAla→Val 
270 81 GCGAAla→Glu   
273 82 GCGAAla→Glu   
278 84 AAA TAA Lys→Stop   
288 87 GCGC Frameshift (−1)   
329 101 CGA TGA Arg→Stop 
353 109 GCG CG Frameshift (−1)   
354 109 GCGTAla→Val   
369 114 CTCGLeu→Arg  
369 114 CTCCLeu→Pro   
377 117 CAA TAA Gln→Stop   
381 118 CGCAArg→His 
528 167 ACAAThr→Lys   
531 168 CGCA Frameshift (−1)   
536 170 GGC CGC Gly→Arg   
542 172 GAG TAG Glu→Stop   
586 186 GCG GC Frameshift (−1)   
588 187 GGGAGly→Asp   
606 193 TCTASer→Stop   
610 194–196 GCGCGTCTGCG a.a. deletion  
620 198–199 CTGGCCT Frameshift (−4)  
620 198 CGTCTG CGTCTGGCTG Frameshift (+4)   
638 204 TAFrameshift (−2)   
653 209 CAA TAA Gln→Stop   
671 215 GAA TAA Glu→Stop   
688 220 TGG TGA Trp→Stop   
693 222 GCGAAla→Asp   
714 229 ACAAThr→Asn   
739 237 ATC AT Frameshift (−1)   
749 241 GCG CCG Ala→Pro   
750 241 GCGAAla→Glu  
770 248 CAG TAG Gln→Stop  
785 253 GCA CA Frameshift (−1)   
786 253 GCGAAla→Glu   
792 255 CGCCArg→Pro   
842 272 GGA AGA Gly→Arg   
843 272 GGGAGly→Glu   
857 277 GAA TAA Glu→Stop   
873 282 TATGTyr→Cys   
877 283 ATC AT Frameshift (−1)   
882 285 CCCTPro→Leu   
917 297 GGG CGG Gly→Arg   
944 306 CAA TAA Gln→Stop   
993 322 TCTGSer→Stop   
1001 325–326 AAAAGA AAAGA Frameshift (−1)   
Nucleotide no.Codon no.MutationAmino acid changeNo. of mutations
TypeaWild typeDetectedHigh EMFLow EMFSham
42 ACATThr→Met  
49 TAC TAA Tyr→Stop  
53 GTC TTC Val→Phe   
56 10 GCA ACA Ala→Thr 
56 10 GCA CCA Ala→Pro   
69 14 GGGTGly→Val   
78 17 TATGTyr→Cys   
82 18 CAG CAC Gln→His   
86 20 GTT TTT Val→Phe  
92 22 CGC TGC Arg→Cys 
93 22 CGCTArg→Leu   
93 22 CGCAArg→His   
95 23 GTG ATG Val→Met  
95 23 GTG TTG Val→Leu   
116 30 GTT TTT Val→Phe   
117 30 GTGGVal→Gly   
117 30 GTGAVal→Asp   
135 36 GAGA Frameshift (−1)   
140 38 GTG ATG Val→Met   
150 41 GCGAAla→Glu   
158 44 GAG TAG Glu→Stop   
174 49 CCCAPro→His   
178 50 AAC AAA Asn→Lys   
179 51 CGC TGC Arg→Cys 
180 51 CGCAArg→His 
185 53 GCA TCA Ala→Ser   
185 53 GCA ACA Ala→Thr  
186 53 GCGTAla→Val   
190 54 CAA CAT Gln→His   
191 55 CAA TAA Gln→Stop  
198 57 GCGTAla→Val 
201 58 GGGTGly→Val   
206 60 CAG TAG Gln→Stop   
215 63 TTGCTG TTGCTGATTGGCTG Frameshift (+8)   
219 64 ATAGIle→Ser   
224 66 GTT TT Frameshift (−1)   
228 67 GCGAAla→Asp   
236 70 AGT TGT Ser→Cys   
270 81 GCGTAla→Val 
270 81 GCGAAla→Glu   
273 82 GCGAAla→Glu   
278 84 AAA TAA Lys→Stop   
288 87 GCGC Frameshift (−1)   
329 101 CGA TGA Arg→Stop 
353 109 GCG CG Frameshift (−1)   
354 109 GCGTAla→Val   
369 114 CTCGLeu→Arg  
369 114 CTCCLeu→Pro   
377 117 CAA TAA Gln→Stop   
381 118 CGCAArg→His 
528 167 ACAAThr→Lys   
531 168 CGCA Frameshift (−1)   
536 170 GGC CGC Gly→Arg   
542 172 GAG TAG Glu→Stop   
586 186 GCG GC Frameshift (−1)   
588 187 GGGAGly→Asp   
606 193 TCTASer→Stop   
610 194–196 GCGCGTCTGCG a.a. deletion  
620 198–199 CTGGCCT Frameshift (−4)  
620 198 CGTCTG CGTCTGGCTG Frameshift (+4)   
638 204 TAFrameshift (−2)   
653 209 CAA TAA Gln→Stop   
671 215 GAA TAA Glu→Stop   
688 220 TGG TGA Trp→Stop   
693 222 GCGAAla→Asp   
714 229 ACAAThr→Asn   
739 237 ATC AT Frameshift (−1)   
749 241 GCG CCG Ala→Pro   
750 241 GCGAAla→Glu  
770 248 CAG TAG Gln→Stop  
785 253 GCA CA Frameshift (−1)   
786 253 GCGAAla→Glu   
792 255 CGCCArg→Pro   
842 272 GGA AGA Gly→Arg   
843 272 GGGAGly→Glu   
857 277 GAA TAA Glu→Stop   
873 282 TATGTyr→Cys   
877 283 ATC AT Frameshift (−1)   
882 285 CCCTPro→Leu   
917 297 GGG CGG Gly→Arg   
944 306 CAA TAA Gln→Stop   
993 322 TCTGSer→Stop   
1001 325–326 AAAAGA AAAGA Frameshift (−1)   
a

1, one base substitution; 2, one base deletion; 3, two or more bases deletion; 4, insertion.

We thank Dr. Ushijima at National Cancer Center Research Institute for valuable comments and statistical analysis.

1
Imaida K., Taki M., Yamaguchi T., Ito T., Watanabe S., Wake K., Aimoto A., Kamimura Y., Ito N., Shirai T. Lack of promoting effects of the electromagnetic near-field used for cellular phones (929.2 MHz) on rat liver carcinogenesis in a medium-term liver bioassay.
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