美國國家環境健康科學研究所（National Institute of Environmental Health Sciences，NIEHS）資助的研究發現，自閉症兒童乳牙的鉛含量比無自閉症兒童高，鋅和錳等重要養分的含量則較低。
自閉症譜系疾患（Autism spectrum disorder，ASD）是複雜的發展障礙，通常幼年期開始出現症狀，影響溝通與社交能力。ASD包含一系列特定行為表現，是一種「譜系疾患」，每個病患的症狀和影響程度有所不同，且沒有任何已知的單一成因。
Baby teeth from children with autism contain more toxic lead and less of the essential nutrients zinc and manganese, compared to teeth from children without autism, according to an innovative study funded by the National Institute of Environmental Health Sciences, NIEHS, part of the National Institutes of Health.
The researchers studied twins to control genetic influences and focus on possible environmental contributors to the disease.
The findings, published today in the journal “Nature Communications,” suggest that differences in early-life exposure to metals, or more importantly how a child’s body processes them, may affect the risk of autism.
Autism spectrum disorder, or ASD, is a complex developmental disability; signs typically appear during early childhood and affect a person’s ability to communicate, and interact with others. ASD is defined by a certain set of behaviors and is a “spectrum condition” that affects individuals differently and to varying degrees. There is no known single cause of autism.
Symptoms include: lack of or delay in spoken language, repetitive use of language or motor mannerisms such as hand-flapping, twirling objects, little or no eye contact and lack of interest in peer relationships.
About one percent of the world population has autism spectrum disorder, according to 2014 figures from the Centers for Disease Control and Prevention in Atlanta.
The NIEHS study shows that the differences in metal uptake between children with and without autism were especially notable during the months just before and after the children were born. The scientists determined this by using lasers to map the growth rings in baby teeth generated during different developmental periods.
The researchers observed higher levels of lead in children with autism throughout development, with the greatest disparity observed during the period following birth.
They also observed lower uptake of manganese in children with autism, both before and after birth. The pattern was more complex for zinc. Children with autism had lower zinc levels earlier in the womb, but these levels then increased after birth, compared to children without autism.
“We think autism begins very early, most likely in the womb, and research suggests that our environment can increase a child’s risk. But by the time children are diagnosed at age 3 or 4, it’s hard to go back and know what the moms were exposed to,” said Cindy Lawler, Ph.D., head of the NIEHS Genes, Environment, and Health Branch. “With baby teeth, we can actually do that.”
Patterns of metal uptake were compared using teeth from 32 pairs of twins and 12 individual twins. The researchers compared patterns in twins where only one had autism, as well as in twins where both or neither had autism.
Smaller differences in the patterns of metal uptake occurred when both twins had autism. Larger differences occurred in twins where only one sibling had autism.
The findings build on prior research showing that exposure to toxic metals, such as lead, and deficiencies of essential nutrients, like manganese, may harm brain development while in the womb or during early childhood. Although manganese is an essential nutrient, it can also be toxic at high doses. Exposure to both lead and high levels of manganese has been associated with autism traits and severity.
The study was led by Manish Arora, Ph.D., an environmental scientist and dentist at the Icahn School of Medicine at Mount Sinai in New York.
With support from NIEHS, Arora and colleagues had previously developed a method that used naturally shed baby teeth to measure children’s exposure to lead and other metals while in the womb and during early childhood.
The researchers use lasers to extract precise layers of dentine, the hard substance beneath tooth enamel, for metal analysis. The team previously showed that the amount of lead in different layers of dentine corresponds to lead exposure during different developmental periods.
The method of using baby teeth to measure past exposure to metals also holds promise for other disorders, such as attention deficit hyperactivity disorder.