巢式PCR法在燃煤型砷中毒患者p16基因启动区的异常甲基化检测中的应用

目的 检测燃煤型砷中毒(地砷病)患者p16基因启动区的异常甲基化情况,探讨p16基因启动区的异常甲基化在地砷病癌变中的作用.方法 采用巢式甲基化特异性PCR法(nMSP)对117例地砷病患者(参考地方性砷中毒诊断标准将其分为轻度中毒组、中度中毒组、重度中毒组)、63例内对照人群和70例外对照人群p16基因启动区的甲基化情况进行了检测.结果 砷中毒病例组甲基化阳性率为39.32%,内对照组阳性率为12.70%,外对照组阳性率为4.29%;其中病例组中轻度、中度和重度组阳性率分别为24.00%,48.89%和54.55%.病例组与外对照组和内对照组比较,差异有统计学意义(P＜0.01).外对照组、内对照组、轻度、中度和重度砷中毒组甲基化阳性率经趋势x2检验,差异有统计学意义(P＜0.01).结论 p16基因启动区的异常甲基化在地砷病人的癌变过程可能起重要作用.     

Investigation on the overlapping endemic of fluorosis and arseniasis related with indoor combustion of high fluorine-arsenic content coal in a mountainous township in Southern Shaanxi Province

目的 调查陕西南部大巴山区燃煤型氟、砷中毒叠加流行的分布规律,为控制陕南燃煤型氟、砷中毒提供科学依据.方法 选择陕西省南部大巴山区紫阳县蒿坪镇,依据国家标准"流行性氟骨症诊断的临床分类(GB 16396-1996)"卫生部 "氟牙症的临床诊断指南(WS/T208-2001)"、"慢性砷中毒诊断指南(WS/T211-2001)"检查全镇27713例,对氟骨症、氟斑牙和砷中毒皮肤损伤进行严重程度分级.以全部居民的数据为标准采用标化发病比(SIR)方法进行性别差异分析,以卡方分析方法进行年龄趋势、症状严重程度趋势以及燃煤型氟、砷中毒关系的分析.结果 陕南紫阳县蒿坪镇地方性氟中毒患病率为56.7%,砷中毒患病率为0.12%;氟砷中毒叠加患病者全体居民中的患病率为6.7%,其中占氟中毒患病的11.85%;随着氟中毒症状严重程度的减轻,氟、砷中毒患者出现的砷中毒症状体征检出率逐渐下降,以中、重症者为明显.结论 长期暴露于燃煤污染的高氟高砷环境的人群可发生氟、砷中毒叠加的临床症状和体征,其中在严重氟中毒患者中叠加砷中毒者,出现中、重度皮肤损伤症状最为显著.     

砷健康损害患者追踪调查

目的 动态观察砷健康损害患者的转归和变化趋势.方法 对440例诊断为砷健康损害的患者分别于8年后及18年后进行随访调查,将砷健康检查所得数据、环境监测数据等输入计算机,用SPSS 10.0统计软件进行处理.结果 8年后患者症状体征阳性率比8年前有显著性增高,距污染源越近砷中毒患者的病情越严重.18年后调查结果显示色素沉着、色素减退、皮肤角化及疣例数有所减少,但有部分调查人群皮肤损伤加重,发展成了不可愈合的溃疡,甚至是皮肤癌.结论 轻度砷健康损害患者随着时间推移,皮肤症状有减轻趋势;但重度砷健康损害患者很难痊愈,甚至可发展成为皮肤癌及肺癌.     

陕南紫阳县蒿坪镇燃煤型氟、砷中毒叠加关系的调查

目的调查陕西南部大巴山区燃煤型氟、砷中毒叠加流行的分布规律,为控制陕南燃煤型氟、砷中毒提供科学依据。方法选择陕西省南部大巴山区紫阳县蒿坪镇,依据国家标准“流行性氟骨症诊断的临床分类（GB16396—1996）”卫生部“氟牙症的临床诊断指南（WS／T208-2001）”、“慢性砷中毒诊断指南（WS／T211-2001）”检查全镇27713例,对氟骨症、氟斑牙和砷中毒皮肤损伤进行严重程度分级。以全部居民的数据为标准采用标化发病比（SIR）方法进行性别差异分析,以卡方分析方法进行年龄趋势、症状严重程度趋势以及燃煤型氟、砷中毒关系的分析。培杲陕南紫阳县蒿坪镇地方性氟中毒患病率为66．7％,砷中毒患病率为0．12％;氟砷中毒叠加患病者全体居民中的患病率为6．7％,其中占氟中毒患病的11．85％;随着氟中毒症状严重程度的减轻,氟、砷中毒患者出现的砷中毒症状体征检出率逐渐下降,以中、重症者为明显。结论长期暴露于燃煤污染的高氟高砷环境的人群可发生氟、砷中毒叠加的临床症状和体征,其中在严重氟中毒患者中叠加砷中毒者,出现中、重度皮肤损伤症状最为显著。     

戊型病毒性肝炎流行动态及临床特征分析

目的 分析了解近年戊型肝炎(HE)的流行动态及临床特征.方法 对2003-2007年5年经血清学检验证实的138例HE病例进行回顾性分析.结果 近5年HE人数占病毒性肝炎住院人数的构成比呈逐年上升趋势.138例均为散发病例,无家庭聚集现象,无集体发病现象.138例中重叠感染31例,重叠组重型肝炎发生率41.92%,较单纯组重症肝炎发生率16.82%有显著增高(P＜0.05).发病人群以50岁以上中老年人居多,占58.69%.其中60岁以上年龄组重症肝炎发生率37.78%较60岁以下年龄组重症肝炎发生率15.05%明显增高(P＜0.05).60岁以上年龄组淤胆型肝炎发生率20.00%较60岁以下年龄组淤胆型肝炎发生率4.30%亦有明显增高(P＜0.05).结论 HE发病率有逐年增高的趋势,重叠感染可加重病情,HE以中老年患者多,临床淤胆型肝炎病例亦多发生于老年患者.     

正己烷中毒患者28例脑电图分析

目的 探讨慢性正己烷中毒对中枢神经系统的损害.方法 对28例临床诊断为正己烷中毒的患者进行脑电图检测,并随机选取30例健康成年人作为对照组.结果 正己烷中毒组有24例患者存在不同程度脑电图异常,占检测总数的85.7%,正常对照组中2例轻度异常(6.7%),2组比较,差异有统计学意义(P＜0.01).结论 正己烷不但可以导致周围神经系统损害,亦可能导致中枢神经系统功能损害.     

陕南燃煤型砷中毒典型村居民的发砷含量特征

目的研究陕南燃煤型地方性砷中毒病区的高砷石煤暴露人群发砷含量与年龄、性别、病情的关系。方法采集病区高砷暴露居民的发样90份,对照村居民的发样14份。用电感耦合等离子体质谱(ICP-MS)测定发砷。结果陕南砷暴露村居民发砷含量显著高于对照村,同时显著高于砷中毒病情更加严重的贵州省兴仁县长青镇,经比较差异均有统计学意义(P<0.05)。高砷暴露人群内部发砷含量随着年龄增加和砷中毒病情加重而增加,符合慢性砷暴露的特征,男性和女性的发砷差异不显著。41名未出现临床体征的居民发砷含量高达7.83 mg/kg,与轻度、中度中毒患者的发砷含量差异无统计学意义(P>0.05),表明在皮肤损伤症状出现之前,砷已经在人体内蓄积并达到有害程度,可能处于亚临床阶段。结论陕南燃煤型砷中毒病区暴露人群具有高砷蓄积特征;无临床体征的高砷暴露人群可能处于亚临床阶段,提示在地方性砷中毒的诊断标准中,应重视发砷值而不能仅注重临床症状和体征。     

肺心病合并砷中毒的治疗与护理

肺心病是老年人常见病、多发病之一,而肺心病患者合并砷中毒则比较少见。肺心病患者合并砷中毒时其中毒症状出现早,病情也往往较重,故其治疗与护理要求有其特珠性。我科自2000年元月以来,收治因砷污染而引起急性、亚急性、慢性砷中毒患者250余例。在250余例中毒患者中,凡原患有其他慢性疾病者,化验检查尿砷、发砷超标虽不严重,但中毒症状较重,起病亦早,特别是原患有肺心病患者合并砷中毒时病情较危重。     

错配修复基因hMLH1和hMSH2甲基化及突变与地方性砷中毒关系

[目的]探讨错配修复基因hMLH1和hMSH2启动子区CpG岛甲基化及第12外显子（exon12）突变与燃煤污染型地方性砷中毒发生发展乃至癌变的关系。[方法]以砷中毒患者110例为病例组,按临床诊断分为轻、中、重度组;按皮肤病理诊断分为非癌变组和癌变组。采用甲基化特异性聚合酶链反应（MSP）法检测其中105例砷中毒患者和82例对照人群外周血中hMLH1和hMSH2基因启动子区的甲基化情况;采用聚合酶链反应-单链构象多态性分析（PCR-SSCP）检测110例砷中毒患者和110例对照人群外周血中hMLH1和hMSH2基因exon12突变情况。[结果]①轻、中、重度组砷中毒患者hMSH2基因甲基化阳性率分别为11.76%、16.28%和32.14%,均明显高于对照组,重度组亦明显高于轻度组（P〈0.05或P〈0.01）;癌变组患者hMLH1和hMSH2基因甲基化阳性率分别为11.11%和27.78%,均明显高于对照组（P〈0.05）;hMLH1和hMSH2基因甲基化阳性率均随临床病情和皮肤病变程度加重而增高（P〈0.05或P〈0.01）。②病例组和对照组均未发现hMLH1和hMSH2基因exon12突变。[结论]错配修复基因hMLH1和hMSH2启动子区甲基化是砷中毒发生发展乃至癌变的早期分子特征,亦可能是导致错配修复功能缺陷的主要方式之一。     

94例职业性慢性砷中毒病例临床特征分析

目的 分析职业性慢性砷中毒病例临床特征.方法 采用临床病例统计及分析的方法总结病例特征.结果 94例砷中毒病例中,93例神经肌电图改变为周围神经源性损害,主要表现为乏力(81.9%)、四肢麻木(85.1%),符合轻度中毒性周围神经病;肝功能异常者34例(36.2%),以谷氨酰转移酶(GGT)改变明显,天冬氨酸转氨酶(AST)、丙氨酸转氨酶(ALT)轻度增高;皮肤瘙痒78例(83.0%),典型皮肤损害者3例(3.2%),其中色素沉着和色素脱失2例,面部溃烂、渗出1例.全部病例接受二巯丙磺钠络合剂驱砷治疗.随访1年后复查肌电图,周围神经功能恢复好转率仅为14.89%.结论 职业性慢性砷中毒最常见为周围神经性病损,其次为肝功能受损,典型皮肤损害最少(可能和砷接触形式、砷化物水平及防护措施等有关,需进一步探讨原因).神经肌电图是一项早期客观诊断和预后判定的有效指标,同时提示砷中毒对周围神经功能的影响可能是长期的.     

Chronic arsenic poisoning from burning high-arsenic-containing coal in Guizhou, China

Arsenic is an environmental hazard and the reduction of drinking water arsenic levels is under consideration. People are exposed to arsenic not only through drinking water but also through arsenic-contaminated air and food. Here we report the health effects of arsenic exposure from burning high arsenic-containing coal in Guizhou, China. Coal in this region has undergone mineralization and thus produces high concentrations of arsenic. Coal is burned inside the home in open pits for daily cooking and crop drying, producing a high concentration of arsenic in indoor air. Arsenic in the air coats and permeates food being dried producing high concentrations in food; however, arsenic concentrations in the drinking water are in the normal range. The estimated sources of total arsenic exposure in this area are from arsenic-contaminated food (50-80%), air (10-20%), water (1-5%), and direct contact in coal-mining workers (1%). At least 3,000 patients with arsenic poisoning were found in the Southwest Prefecture of Guizhou, and approximately 200,000 people are at risk for such overexposures. Skin lesions are common, including keratosis of the hands and feet, pigmentation on the trunk, skin ulceration, and skin cancers. Toxicities to internal organs, including lung dysfunction, neuropathy, and nephrotoxicity, are clinically evident. The prevalence of hepatomegaly was 20%, and cirrhosis, ascites, and liver cancer are the most serious outcomes of arsenic poisoning. The Chinese government and international organizations are attempting to improve the house conditions and the coal source, and thereby protect human health in this area.     

饮水型地方性砷中毒患者皮肤损伤与甲基化代谢关系

目的 探讨饮水型砷中毒患者皮肤损伤与甲基化代谢能力的关系。方法 依据诊断标准对某饮水型砷中毒病区患者症状进行分级,测定血中无机砷(iAs)、甲基砷(MMA)、二甲基砷(DMA)含量并计算百分比(iAs%、MMA%、DMA%),以iAs、MMA及DMA的总和表示总砷(tAs)水平,以(MMA+DMA)/tAs及DMA/(MMA+DMA)分别计算一甲基化率(FMR)和二甲基化率(SMR)水平。结果 患者血中形态砷和甲基化指标水平在性别间差异无统计学意义(P>0.05);轻、中、重度患者FMR水平差异无统计学意义(P>0.05);中度及重度患者SMR水平[(0.36±0.11)、(0.37±0.08)]均低于轻度患者(0.48±0.11),MMA%[(0.50±0.06)、(0.52±0.03)]均高于轻度患者(0.41±0.09);SMR水平与患者皮肤损伤症状等级之间呈负相关(r=-0.429,P<0.05)。结论 SMR水平下降及MMA%水平增高与砷性皮肤损伤关系密切。     

集中式改水防治地方性砷中毒的近期效果评价

目的 评价集中式改水对砷暴露人群的近期防治效果。方法 选择内蒙古包头市缸房营村饮水型砷中毒高发病区，观察改水前和集中式改水1年后砷暴露人群的皮肤损伤恢复情况；原子吸收分光光度法测定尿总砷和形态砷含量；ELISA方法测定尿8-羟基-2’-脱氧鸟苷(8-OH-dG)含量。结果 集中式改水1年后砷暴露人群的皮肤损伤有明显恢复；尿总砷和形态砷含量、尿8-OH-dG含量均明显降低。结论 在饮水型中毒病区集中式改水除砷是一种有效的干预措施。改水1年使砷暴露人群的皮肤损伤明显改善，DNA氧化损伤明显降低。     

5,10-亚甲基四氢叶酸还原酶基因C677T位点突变与地方性砷中毒皮肤病变发生关系的研究

目的　 5 ,10- 亚甲基四氢叶酸还原酶 (MTHFR)是叶酸代谢关键酶 ,旨在了解该酶基因C6 77T位点突变是否是地方性砷中毒皮肤病变发生的遗传易感因素。方法　选择 5 0名出现砷性皮肤病变居民作为皮肤病变组 ,以同地区饮水砷浓度相近的 35名正常人作为对照 ,进行MTHFR基因C6 77T位点多态性分析(PCR- RFLP法 )、血清叶酸测定 (微生物法 )和维生素B1 2 测定 (电化学发光法 )。结果　皮肤病变组MTHFR基因C6 77T位点TT基因型占 34. 0 % ,T等位基因频率为 5 6 . 0 %。皮肤病变组和对照组基因型构成和等位基因频率差异无显著性。两组血清叶酸、VitB1 2 水平差异均无显著性。以血清叶酸水平≥ 10. 5nmol L且CC基因型作为参照 ,其它组粗OR值和经Logistic回归分析控制性别、年龄、水砷浓度、吸烟后的校正OR值均大于 1,但 95 %CI包含 1。结论　MTHFR基因C6 77T位点多态性与地方性砷中毒皮肤病变的发生无明显关联。     

Urinary arsenic metabolites of subjects exposed to elevated arsenic present in coal in Shaanxi Province, China

In contrast to arsenic (As) poisoning caused by naturally occurring inorganic arsenic-contaminated water consumption, coal arsenic poisoning (CAP) induced by elevated arsenic exposure from coal combustion has rarely been reported. In this study, the concentrations and distributions of urinary arsenic metabolites in 57 volunteers (36 subjects with skin lesions and 21 subjects without skin lesions), who had been exposed to elevated levels of arsenic present in coal in Changshapu village in the south of Shaanxi Province (China), were reported. The urinary arsenic species, including inorganic arsenic (iAs) [arsenite (iAsIII) and arsenate (iAsV)], monomethylarsonic acid (MMAV) and dimethylarsinic acid (DMAV), were determined by high-performance liquid chromatography (HPLC) combined with inductively coupled plasma mass spectroscopy (ICP-MS). The relative distributions of arsenic species, the primary methylation index (PMI=MMAV/iAs) and the secondary methylation index (SMI=DMAV/MMAV) were calculated to assess the metabolism of arsenic. Subjects with skin lesions had a higher concentration of urinary arsenic and a lower arsenic methylation capability than subjects without skin lesions. Women had a significantly higher methylation capability of arsenic than men, as defined by a higher percent DMAV and SMI in urine among women, which was the one possible interpretation of women with a higher concentration of urinary arsenic but lower susceptibility to skin lesions. The findings suggested that not only the dose of arsenic exposure but also the arsenic methylation capability have an impact on the individual susceptibility to skin lesions induced by coal arsenic exposure.     

Arsenic-related health problems among hospital patients in southern Bangladesh

To assess the health effects of arsenic poisoning and to determine the relationship among duration and severity of skin lesions, exposure dose of arsenic, and nutritional status of people, 150 patients attending the Dermatology Outpatients Department of Sher-e-Bangla Medical College Hospital, Barisal, Bangladesh, were included in this cross-sectional study. The study was conducted during January-December 2000. Records of patients were collected prospectively using a pre-tested questionnaire, which included information on demography, sources of water for drinking and cooking, duration and amount of drinking-water obtained from shallow tubewells, clinical presentations, complications, and physical and laboratory findings. Water samples from tubewells currently being used by individual patients were examined. Nine percent of the patients were unaware that arsenic-contaminated water causes diseases. Due to lack of alternative water supplies, 25% of the subjects were still drinking water from contaminated tubewells. About 18% did not complain of any clinical symptoms, except that their skin lesions were ugly-looking, and 82% had moderate or severe skin lesions. Thirty-one percent of the water samples had arsenic concentrations 10-fold higher than the permissible limit of 0.05 mg/L in Bangladesh and 50-fold higher than the WHO guideline value of 0.01 mg/L. The mean arsenic concentration in water was significantly associated with the severity of disease. Body mass index correlated inversely (r = -0.298, p = 0.013) with the duration of disease after controlling for age. The findings suggest the need to enhance public awareness on negative health effects of arsenic poisoning in rural Bangladesh. From a public-health perspective, effective intervention strategies need to be developed to curb the exposure, strengthen rapid diagnostic facilities, establish effective treatment facilities in rural areas, and improve the nutritional status of people.     

Prevalence of arsenic exposure and skin lesions. A population based survey in Matlab, Bangladesh

STUDY OBJECTIVE: To assess prevalence of arsenic exposure through drinking water and skin lesions, and their variation by geographical area, age, sex, and socioeconomic conditions. DESIGN, SETTING, AND PARTICIPANTS: Skin lesion cases were identified by screening the entire population above 4 years of age (n = 166,934) living in Matlab, a rural area in Bangladesh, during January 2002 and August 2003. The process of case identification involved initial skin examinations in the field, followed by verification by physicians in a clinic, and final confirmation by two independent experts reviewing photographs. The tubewell water arsenic concentrations (n = 13,286) were analysed by atomic absorption spectrometry. Drinking water history since 1970 was obtained for each person. Exposure information was constructed using drinking water histories and data on water arsenic concentrations. MAIN RESULTS: The arsenic concentrations ranged from <1 to 3644 microg/l, and more than 70% of functioning tubewells exceeded the World Health Organisation guideline of 10 microg/l. Arsenic exposure had increased steadily from 1970s to the late 1990s, afterwards a decrease could be noted. In total, 504 skin lesions cases were identified, and the overall crude prevalence was 3/1000. Women had significantly higher cumulative exposure to arsenic, while men had significantly higher prevalence of skin lesions (SMR 158, 95% CI 133 to 188). The highest prevalence occurred in 35-44 age groups for both sexes. Arsenic exposure and skin lesions had a positive association with socioeconomic groups and achieved educational level. CONCLUSIONS: The result showed sex, age, and socioeconomic differentials in both exposure and skin lesions. Findings clearly showed the urgency of effective arsenic mitigation activities.     

Arsenic groundwater contamination in Middle Ganga Plain,Bihar, India: a future danger?

The pandemic of arsenic poisoning due to contaminated groundwater in West Bengal, India, and all of Bangladesh has been thought to be limited to the Ganges Delta (the Lower Ganga Plain), despite early survey reports of arsenic contamination in groundwater in the Union Territory of Chandigarh and its surroundings in the northwestern Upper Ganga Plain and recent findings in the Terai area of Nepal. Anecdotal reports of arsenical skin lesions in villagers led us to evaluate arsenic exposure and sequelae in the Semria Ojha Patti village in the Middle Ganga Plain, Bihar, where tube wells replaced dug wells about 20 years ago. Analyses of the arsenic content of 206 tube wells (95% of the total) showed that 56.8% exceeded arsenic concentrations of 50 micro g/L, with 19.9% > 300 micro g/L, the concentration predicting overt arsenical skin lesions. On medical examination of a self-selected sample of 550 (390 adults and 160 children), 13% of the adults and 6.3% of the children had typical skin lesions, an unusually high involvement for children, except in extreme exposures combined with malnutrition. The urine, hair, and nail concentrations of arsenic correlated significantly (r = 0.72-0.77) with drinking water arsenic concentrations up to 1,654 micro g/L. On neurologic examination, arsenic-typical neuropathy was diagnosed in 63% of the adults, a prevalence previously seen only in severe, subacute exposures. We also observed an apparent increase in fetal loss and premature delivery in the women with the highest concentrations of arsenic in their drinking water. The possibility of contaminated groundwater at other sites in the Middle and Upper Ganga Plain merits investigation.     

Protective effects of B vitamins and antioxidants on the risk of arsenic-related skin lesions in Bangladesh

BACKGROUND: An estimated 25-40 million of the 127 million people of Bangladesh have been exposed to high levels of naturally occurring arsenic from drinking groundwater. The mitigating effects of diet on arsenic-related premalignant skin lesions are largely unknown. OBJECTIVES: The purpose of this study was to clarify the effects of the vitamin B group (thiamin, riboflavin, niacin, pyridoxine, and cobalamin) and antioxidants (vitamins A, C, and E) on arsenic-related skin lesions. METHODS: We performed a cross-sectional study using baseline data from the Health Effects of Arsenic Longitudinal Study (HEALS), 2000-2002, with individual-level, time-weighted measures of arsenic exposure from drinking water. A total of 14,828 individuals meeting a set of eligibility criteria were identified among 65,876 users of all 5,996 tube wells in the 25-km(2) area of Araihazar, Bangladesh; 11,746 were recruited into the study. This analysis is based on 10,628 subjects (90.5%) with nonmissing dietary data. Skin lesions were identified according to a structured clinical protocol during screening and confirmed with further clinical review. RESULTS: Riboflavin, pyridoxine, folic acid, and vitamins A, C, and E significantly modified risk of arsenic-related skin lesions. The deleterious effect of ingested arsenic, at a given exposure level, was significantly reduced (ranging from 46% reduction for pyridoxine to 68% for vitamin C) for persons in the highest quintiles of vitamin intake. CONCLUSIONS: Intakes of B-vitamins and antioxidants, at doses greater than the current recommended daily amounts for the country, may reduce the risk of arsenic-related skin lesions in Bangladesh.     

A pathway-based analysis of urinary arsenic metabolites and skin lesions

Inorganic arsenic is metabolized to monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA). Limited evidence suggests that the ability to fully metabolize arsenic into DMA influences susceptibility to disease. To determine whether percentage of MMA was predictive of disease, the authors used data from a case-control study conducted in Bangladesh (2001-2003). Persons who were diagnosed with keratosis, melanosis, Bowen's disease, or squamous cell carcinoma were matched on age, sex, and village to persons without these conditions. This analysis was restricted to persons who had no missing data on covariates (859 cases, 868 controls). A path analysis was used to evaluate simultaneously the association between the percentage of all urinary arsenic metabolites and the odds of skin lesions using PROC CALIS in SAS, version 9.1 (SAS Institute, Inc., Cary, North Carolina) and Mplus, version 6.1 (Muthén & Muthén, Los Angeles, California). The odds of skin lesions were significantly associated with log(10) percentage of MMA (adjusted odds ratio (OR(adj)) = 1.56, 95% confidence interval (CI): 1.15, 2.12) but not log(10) percentage of inorganic arsenic (OR(adj) = 1.06, 95% CI: 0.75, 1.50) or log(10) percentage of DMA (OR(adj) = 1.07, 95% CI: 0.33, 3.46). This novel analysis confirmed that persons who excrete a higher proportion of MMA have a greater risk of skin lesions after data are adequately controlled for urinary arsenic metabolites, current arsenic exposure, and other risk factors.