帕金森病如今是美国第二常见的神经疾病，每年约有 90,000 人被诊断，过去 30 年其盛行率已翻倍。研究预测未来每个十年还将再上升 15% 到 35%，这种走势与主要由遗传决定的疾病并不相符。尽管如此，超过一半的研究经费仍流向遗传学，而已知基因变异只能完全解释约 10% 到 15% 的病例，显示多达 75% 到 90% 可能由环境暴露所驱动。

越来越多证据指向三氯乙烯（TCE），这种广泛使用的溶剂已污染饮用水数十年。在 Camp Lejeune，海军陆战队员大约 35 年来在不知情下吸入 TCE 水汽，其退伍军人肾癌风险高出 35%，何杰金氏淋巴瘤高出 47%，多发性骨髓瘤高出 68%，罹患帕金森病的风险则比饮用未受污染 Camp Pendleton 水源者高出 70%。小鼠吸入实验重现这种暴露，显示多巴胺神经元严重流失，并促使美国环保署推动禁止 TCE。

更广泛的数据也强调环境的重要性：在一项约 50 万名英国人的研究中，生活方式与暴露被发现对早逝的影响约为遗传的 10 倍。遗传学家现在估计，只有约 5% 的疾病是纯遗传性的，少于 40% 的疾病具有任何遗传成分；包括乳癌、冠心病和类风湿性关节炎在内的许多慢性病，其遗传占比仅约 20%。同时，美国超过 75% 的成年人罹患某种慢性疾病，自闭症诊断率则从 1/10,000 飙升至 1/36。

Parkinson’s disease is now the second most common neurological disorder in the US, with about 90,000 new diagnoses each year, and its prevalence has doubled over the past 30 years. Studies project a further 15–35 percent increase in each coming decade, behavior inconsistent with a mainly inherited disorder. Yet more than half of research funding has gone to genetics even though only about 10–15 percent of cases are fully explained by known variants, suggesting 75–90 percent may be driven by environmental exposures.

Evidence increasingly points to trichloroethylene, or TCE, a widespread solvent that has contaminated drinking water for decades. At Camp Lejeune, where Marines unknowingly inhaled TCE vapors for roughly 35 years, veterans show 35 percent higher kidney cancer rates, 47 percent higher Hodgkin’s lymphoma, 68 percent higher multiple myeloma, and 70 percent higher Parkinson’s risk than those at uncontaminated Camp Pendleton. Mouse inhalation studies replicate this exposure, showing severe loss of dopamine neurons, and helped prompt the US Environmental Protection Agency to move to ban TCE.

Broader data reinforce the primacy of environment: in a study of about 500,000 Britons, lifestyle and exposures were found to be roughly 10 times more important than genetics in explaining early death. Geneticists now estimate only around 5 percent of diseases are purely genetic and less than 40 percent have any genetic component; many chronic conditions, including breast cancer, coronary heart disease, and rheumatoid arthritis, are only about 20 percent genetic. Meanwhile, US chronic illness affects over 75 percent of adults, and autism diagnoses have surged from 1 in 10,000 to 1 in 36.