ワクチン否定論者が次に言うこと by New York Times

FDA is continuing its efforts toward reducing or removing thimerosal from all existing vaccines. Much progress has been made to date. FDA has been actively working with manufacturers, particularly those that manufacture childhood vaccines, to reach the goal of eliminating thimerosal from vaccines, and has been collaborating with other PHS agencies to further evaluate the potential health effects of thimerosal. Since 2001, all vaccines recommended for children 6 years of age and younger have contained either no thimerosal or only trace amounts, with the exception of inactivated influenza vaccines, which are marketed in both the preservative-free and thimerosal-preservative-containing formulations. Thimerosal-preservative free influenza vaccine licensed for use in children six to 59 months of age is available in limited supply. Nevertheless, FDA is in discussions with manufacturers of influenza vaccine regarding their capacity to increase the supply of vaccine without thimerosal as a preservative. Additionally, new pediatric vaccines that have received licensure do not contain thimerosal.


[Thimerosal in Vaccines Questions and Answers on FDA]
しかし、NY Timesによれば、ワクチン否定論者たちの中には別の理屈を持ち出して、ワクチンと自閉症の関連を主張している者もいるという:
In the United States, anti-vaccine groups have advanced other theories since then to explain why they think vaccines cause autism. For years, they blamed thimerosal, a vaccine preservative containing mercury. Because of concerns over the preservative, vaccine makers in 2001 largely eliminated thimerosal from routinely administered childhood vaccines.


But this change has had no apparent impact on childhood autism rates. Anti-vaccine groups now suggest that a significant number of children have a cellular disorder whose effects are set off by vaccinations.


With each new theory, parents’ groups have called for research to explore possible links between vaccination and autism. Study after study has failed to show any link, and prominent scientific agencies have concluded that scarce research dollars should be spent investigating other possible causes of autism.


[GARDINER HARRIS: "Journal Retracts 1998 Paper Linking Autism to Vaccines" (2010/02/02) on NY Times]
ここで、ワクチン否定論者たちが持ち出してきた細胞欠陥(Cellular disorder)とは、ミトコンドリア呼吸鎖異常症(mitochondrial respiratory chain disorder)のことで、自閉症との関係を示唆する研究としては、Oliveira et al[2005]がある:
Oliveira G et al.: "Mitochondrial dysfunction in autism spectrum disorders: a population-based study", Developmental Medicine & Child Neurology (2005), 47:3:185-189


A minority of cases of autism has been associated with several different organic conditions, including bioenergetic metabolism deficiency. In a population-based study, we screened associated medical conditions in a group of 120 children with autism (current age range 11y 5mo to 14y 4mo, mean age 12y 11mo [SD 9.6mo], male:female ratio 2.9:1). Children were diagnosed using Diagnostic and Statistical Manual of Mental Disorders criteria, the Autism Diagnostic Interview – Revised, and the Childhood Autism Rating Scale; 76% were diagnosed with typical autism and 24% with atypical autism. Cognitive functional level was assessed with the Griffiths scale and the Wechsler Intelligence Scale for Children and was in the normal range in 17%. Epilepsy was present in 19 patients. Plasma lactate levels were measured in 69 patients, and in 14 we found hyperlactacidemia. Five of 11 patients studied were classified with definite mitochondrial respiratory chain disorder, suggesting that this might be one of the most common disorders associated with autism (5 of 69; 7.2%) and warranting further investigation.

New Scientistによれば、これがワクチン否定論とリンクして動き始めたのは2008年3月の出来事によるものだという:
JUST as the dispute over whether vaccines cause autism was dying down at last, a US government decision has added fresh fuel to the fire. Last week it emerged that the federal government is to compensate a couple who say that the regular childhood vaccines, given to their baby daughter in 2000, caused her to develop autism. Damages have not yet been set, but could exceed $1 million.


Significantly, the government's decision says nothing about whether vaccines cause autism. Instead, government lawyers concluded only that vaccines aggravated a pre-existing cellular disorder in the child, causing brain damage that included features of autism. Nonetheless, anti-vaccination campaigners are claiming vindication. "It's official," wrote one autism blogger. "The sky has fallen. The fat lady has sung. Pigs are flying."

[Autism payout reignites vaccine controversy (2008/03/08) on New Scientist]
しかし、New Scientistによれば、そもそもミトコンドリア障害は稀であり、かつミトコンドリア障害であれば、いずれは様々な成長障害を起こすことになり、前記の政府判断はおかしい:
Researchers contacted by New Scientist say that in very crude terms, children with mitochondrial disorders are especially at risk of neurological and muscular abnormalities because muscle and brain cells need so much energy. If mitochondria are faulty and don't supply enough energy, these cells are damaged. Lack of energy can also lead to encephalopathy, or disruption of brain structure, which can in turn cause autism-like symptoms. "Anything that messes up development can cause something that looks like autism," says Lindsey Kent of the University of St Andrews in the UK. But such symptoms are unusual. Mostly, children present with a wide range of developmental disorders of varying severity.

Kent also points out that mitochondrial diseases are very rare - just 5.7 per 100,000 individuals worldwide - and the subsets of disorders linked with autism even rarer. Kent says she is surprised that the court ruled in favour of the girl, arguing that the symptoms would probably have developed whether or not she had been vaccinated. "She has a clear mitochondrial genetic mutation, which is probably the cause of her developmental regression, autistic features and epilepsy," she says. "Whether or not the vaccine unmasked this will never be known, but it seems quite surprising."

NewScientist誌が連絡を取った研究者は、非常に露骨な表現で、筋肉や脳細胞は大量にエネルギーを必要とするため、ミトコンドリア障害の子供たちには特に神経系や筋肉の異常のリスクがある。ミトコンドリアが不完全で十分なエネルギーを供給できないと、これらの細胞は損傷する。エネルギー不足は脳症あるいは脳構造の破壊につながることもある。そして、それは自閉症のような症状を引き起こすこともありうる。「成長を阻害するような何らかの障害は、それが何であれ、自閉症のように見える症状を引き起こしうる」と英国University of st AndrewsのLindsey Kentは言う。しかし、そのような症状はあまり見られるものではない。大半の場合、子供は様々な成長障害を呈する。


Salvatore DiMauro, who has studied links between autism and mitochondrial mutations at Columbia University in New York, agrees. "My guess is that if she had a mitochondrial mutation, sooner or later she would have shown something abnormal," he says.

DiMauro says it's significant that the girl's genetic mutation was in the 16S ribosomal RNA gene, because these are very rare. Only four others are known. The gene plays a pivotal role in protein production, so any mutation that damages this function could have a huge impact on other mitochondrial genes and energy production by cells. "In the girl's case it would be important to prove protein synthesis is disrupted," he says.

DiMauro adds that in children who are "energy-challenged" because of mitochondrial disease, stresses including vaccination could trigger autism-like symptoms. "Children get worse in any stressful event, from having flu to having a vaccination," he says.

ミトコンドリアの突然変異と自閉症の関係を研究しているニューヨークのColumbia UniversityのSalvatore DiMauroは、このKentの見解に同意する。「もし彼女にミトコンドリア突然変異があるとすれば、遅かれ早かれ彼女には何らかの障害が出ていただろうと思う。



[Autism payout reignites vaccine controversy (2008/03/08) on New Scientist]
Dr. Andrew Wakefieldの失墜により、今後はこっちに乗り換えるワクチン否定論者が増えると思われる。

The prevalence of autism is about 1–2 per 1,000 people; the prevalence of ASD is about 6 per 1,000, with about four times as many males as females. The number of people diagnosed with autism has increased dramatically since the 1980s, partly due to changes in diagnostic practice; the question of whether actual prevalence has increased is unresolved.[8]
Newschaffer CJ, Croen LA, Daniels J et al. (2007). "The epidemiology of autism spectrum disorders" (PDF). Annu Rev Public Health 28: 235–58. doi:10.1146/annurev.publhealth.28.021406.144007. PMID 17367287.
Oliveira et al[2005]ではミトコンドリア障害が目立つが、ミトコンドリア障害な人の比率 6/100000 vs 自閉症とASDな人の比率 8/1000 から見て、大半の自閉症とASDはミトコンドリア障害を持っていない。さらに、因果関係を示す証拠もない。したがって、これからのワクチン否定論者たちは、フィクションを主張し続けることになるだろう。

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Excerpt: ■自閉症とミトコンドリア(日本自閉症協会掲示板) この件については以下のkumicitさんの記事をご参照ください。Andrew WakefieldらによるMMRワクチン自閉症原因説の論文がLence..
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Tracked: 2011-02-20 16:15