Tracing the Origins of Autism: A Spectrum of New Studies - Long

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Tracing the Origins of Autism: A Spectrum of New Studies(How to Love the NIEH. This report quotes Dr. Ian Lipkin and Mark Blaxill, to its credit.)http://www.ehponline.org/members/2006/114-7/focus.htmlEnvironmental Health Perspectives Volume 114, Number 7, July 2006 - Full (PDF)- Related EHP Articles - PubMed:Related Articles- PubMed:Citation- Cited in PMC- Purchase This Issue The etiology of a medical condition might

seem an unlikely subject to arouse intense feelings.

Yet few medical disorders have stirred up as

much passion and divisiveness among scientists

and the general public as autism has in recent

years. The heat of the controversy has even attracted

attention from periodicals such as The Wall

Street Journal, the Columbia Journalism

Review, and Wired magazine—seemingly

improbable forums for a medical debate. Why all

the furor?

At the eye of the storm is the startling climb

in the numbers of children who have been diagnosed

with one of the autism spectrum disorders (ASDs).

The most severe ASD is autistic disorder (which

often is called simply "autism");

other forms include Asperger syndrome and the

much rarer childhood disintegrative disorder.

In the United States, the diagnosis of ASDs increased

roughly 10-fold over the course of a decade,

from 4–5 children per 10,000 in the 1980s

to 30–60 children per 10,000 in the 1990s,

according to a report in the August 2003 Journal

of Autism and Developmental Disorders. The

5 May 2006 issue of Morbidity and Mortality

Weekly Report describes the results

of two parent surveys from 2003 and 2004, which

suggested that 55–57 children per 10,000

had autism (however, an editorial note points

out that, due to the nature of the surveys, parents

of children with other ASDs may have reported

their children as having autistic disorder).

Some scientists believe that much of the upsurge is the result of

increased awareness of ASDs or changes in diagnostic criteria, which

would suggest that the true prevalence of the disorders has been stable

over time. Others disagree. "It is premature to state that there is no

increase in prevalence, " says W. Ian Lipkin, a professor of neurology,

anatomy, and neurobiology at Columbia University. "None of the studies

to date has been designed to definitively address the issue. "

The prevalence of ASDs plays into the fundamental

question of what causes these disorders. If the

number of cases is truly on the rise, then it

would seem likely that some change in the environment

is driving up the total. That's partly

what has divided scientists into opposing camps—they

cannot agree on the relative importance of genetic

and environmental factors in the disorders' etiology.

Alas, answering the prevalence question might

not end that debate. "Even if the prevalence

of autism were stable," says Lipkin, "you

would not be able to rule out the possibility

of an environmental trigger." That's

because very little is known about the mechanisms

that cause autism, be they environmental or genetic.

"The study of autism was, until recently,

largely dominated by the field of psychology,

where characterizing the behaviors and developing

reliable instruments for diagnosis have been

major areas of research over the past few decades," says

Irva Hertz-Picciotto, an epidemiologist at the

University of California, .

Indeed, the core symptoms of ASDs—social

disinterest, repetitive and overly focused behavior,

and problems in communication, usually appearing

before 3 years of age—have been well described.

Much less research has focused on the causes

of these symptoms.

Several investigations dating back to the 1970s

indicate that identical twins have a much higher

concordance rate of ASDs than fraternal twins,

according to a report in the Spring 1998 issue

of Mental Retardation and Developmental Disabilities

Research Reviews. Those studies provide some

of the best evidence that these disorders have

a strong genetic component. But the identity

of the genes involved, much less how they produce

ASDs, has not been established. Moreover, the

concordance rate for identical twins is not 100%,

which suggests that at least some cases must

be associated with environmental or epigenetic

factors.

A few cases of ASDs have been clearly linked

to environmental insults. These include prenatal

exposure to chemical agents such as thalidomide

and valproic acid, as well as to infectious agents

such as the rubella and influenza viruses. Here

again, the concordance rate is not 100%, which

suggests that a genetic predisposition is necessary

for chemical and microbial factors to act as

triggers.

Tantalizing clues like these are prompting

scientists to reconsider the research agenda

for ASDs. Martha Herbert, a pediatric neurologist

at Harvard Medical School, and her colleagues

have been applying the methods of genomics to

identify environmentally responsive genes that

might be important in these disorders.

"When you realize that the widespread

changes we're seeing in autistic brains

may occur in parallel with or even downstream

from widespread changes in the body—such

as in the immune system—and that these

changes may be environmentally triggered, you

start looking for ways to think more broadly

about genetic vulnerability. It can't be

just about `brain genes,'" Herbert

says.

Some new epidemiological studies also are looking

for gene–environment interactions. According

to Schendel, an epidemiologist and project

officer for autism research at the CDC, which

funds one of the projects, these initiatives

will be able to examine many possible causal

pathways to ASDs, including both genetic and

environmental causes that may lead to the development

of the disorders in different subgroups of children.

Some of these projects are already under way,

whereas others will begin soon. All of the scientists

involved, however, believe their research will

finally provide some of the answers that everyone

has been looking for.

CHARGE

The Childhood Autism Risks from Genetics and

the Environment (CHARGE) project is unique

among the large ASD epidemiological studies.

It focuses solely on autistic disorder, and it

emphasizes a search for environmental factors—including

a broad array of chemicals in food, consumer

products, and ambient air, as well as infectious

and medical exposures—that might be linked

to the disorder. The study is funded by the NIH.

CHARGE is a case–control study in which a group of autistic children

aged 2 to 5 years is compared to a group of age-matched controls in a

population-based study. "Because of the California Department of

Developmental Services' system of Regional Centers [nonprofit

corporations that coordinate health care services and support for

citizens with developmental disabilities], we have a handle on

enumerating a high proportion of the children newly diagnosed with

autism in our defined area over a specific time period," says

Hertz-Picciotto, the principal investigator of the CHARGE study.

"Similarly, we can enumerate the children in the same area and time

period who are not cases. We then sample from both. "

The project was initiated in 2002 with the

goal of recruiting 1,000 to 2,000 children. Half

of the children will be autistic. The other half

will make up two control groups: one group of

children with developmental delays (but not an

ASD) and a second group of children selected

from the general population without regard to

developmental characteristics.

The advantage of the case–control design

is that scientists can acquire large numbers

of children with the disorder. By comparison,

in a cohort design researchers would need a very

large sample size, given the prevalence of autism,

to acquire the same number of cases.

Hertz-Picciotto expects to have enrolled nearly 700 children by August

2006, the end of the first funding period. "I've applied for another

five-year grant," she says, "and I hope to be funded to enroll nine

hundred in that round, which would bring us to sixteen hundred

children. "

The CHARGE team is looking at possible exposures

during the prenatal period and early childhood.

Some of the data will be gathered through comprehensive

interviews with parents, but Hertz-Picciotto

admits that this is not the best way to look

for exposures. "You ask people questions,

and their answers may be colored by the fact

that they know they have a child with a condition," she

says. "They may spend a lot of time thinking

about what they might have done or what might

have gone wrong, and they may have preconceived

ideas about what caused [the disorder]. They

might not be as objective." Such problems

with postdiagnosis interview information are

recognized as a weakness of retrospective studies.

The scientists are getting around this issue

by examining each child's medical records

and those of the mother during pregnancy and

delivery—nonsubjective data gathered in

the course of routine obstetric care. They are

also collecting blood, urine, and hair specimens

that will be analyzed in the laboratory.

The study has already provided some intriguing

leads. "We're finding that the immune

system seems to function at a lower level in

autism," says Hertz-Picciotto. "That's

an important clue. It could mean that whatever

causes autism also disrupts the immune system,

or it could be that the immune system disrupts

neural development so that something goes awry

in laying down brain circuitry prenatally or

in the early postnatal period." [For more

information on the CHARGE study, see p.

1119, this issue.]

ABC

The Autism Birth Cohort (ABC) Study, now under

way in Norway, is a large prospective design

that is expected to gather information on 100,000

babies. The work is being led by scientists at

the Mailman School of Public Health at Columbia

University, who are collaborating with colleagues

at the Norwegian Institute of Public Health,

with funding from the U.S. National Institute

of Neurological Disorders and Stroke.

"When you want to know why some people

are more at risk than others in a population,

then that's best answered using a cohort

design," says Ezra Susser, an epidemiologist

at Columbia University and a co-investigator

on the ABC project. "When we think about

environmental causes of [ASDs], we're probably

interested in phenomena that occur prior to birth

or perhaps shortly after birth. So you want to

collect prospective data from people as early

as possible in pregnancy." Because ASDs

are not common, the study will need large numbers

of children to have enough statistical power,

according to Susser.

So far the ABC team has recruited 75,000 pregnant

Norwegian mothers, but Susser is hoping for more. "We've

got enough to look for an environmental risk

factor, but you need larger numbers for studying

gene–environment interactions, which could

turn out to be important," he says. It's

possible the team could acquire greater numbers

by collaborating with other studies. One candidate

for collaboration is the Avon Longitudinal Study

of Parents and Children in the United Kingdom,

which is looking at the complex ways in which

environmental features may relate to optimal

development and health in children. But there's

been no agreement yet, Susser says.

image:

Corbis

Even so, the ABC scientists are optimistic about their study. "Little

is known about the natural history of [ASDs]," says Lipkin, who is the

principal investigator of the project. "By starting prenatally, we're

collecting detailed, critical information about environmental exposures

in an unbiased fashion. "

The scientists are also collecting plasma,

serum, RNA, and DNA. "We have extraordinary

biological materials," says Lipkin. "We

can pursue biomarkers as well as exposure to

toxicants and infection. We also have maternal

DNA, paternal DNA, and the child's DNA

[so-called trio data]; thus we can look for the

appearance of novel mutations," he adds.

The ABC researchers will follow the children

through time, with parents answering questionnaires

about the health and social interactions of their

children as they reach 6, 18, and 36 months of

age. "It may be that the developmental

trajectory tells us much more than a single time

point can ever tell us about the pathogenesis

of [ASDs]," says Mady Hornig, a physician-scientist

at Columbia University who participates in the

project.

Despite their enthusiasm for the project's

potential, the ABC scientists feel they could

accomplish much more if they only had the funding. "The

pity of it is we have no money to do the biological

work," says Lipkin. "We can collect

the samples and do the questionnaires, but we've

been unable to get funding to look for any of

the environmental factors. We're collecting

blood, but we won't know whether there's

a biomarker until we do a biomarker analysis.

We have funds to collect RNA, but in order to

do the transcript profiling we need approximately

four hundred dollars per sample," he says.

Lipkin adds that there's only so much

that one can do with questionnaire data. "We

do ask about infection and diet, but that's

not the same as having a lab value that can validate

what was reported, and then look at a direct

correlation with the outcome," he says.

Lipkin believes that part of the problem is

that searching for environmental factors goes

against the current research paradigm in ASDs. "The

focus is on genetic factors," he says. "Infectious

diseases, toxicology, and immunology receive

short shrift. The ABC is clearly the right opportunity

to pursue these other leads because we have the

ideal samples to survey prenatally and postnatally," he

says.

The scientists are just now receiving the responses

to the 36-month questionnaire. "It'll

probably be another two years before we have

our first report," Hornig says. Funds are

now in place to study the children at 36 months;

however, the team hopes to follow them for a

lifetime, according to Hornig.

CADDRE

In response to the Children's Health

Act of 2000, the CDC established and funds six

Centers for Autism and Developmental Disabilities

Research and Epidemiology (CADDRE) to investigate

potential risk factors for ASDs. The multisite

approach offers a study group that is geographically

and demographically more representative of the

general U.S. population than a smaller regional

study could provide, according to Craig Newschaffer,

an epidemiologist and principal investigator

at the s Hopkins Bloomberg School of Public

Health CADDRE site.

According to Newschaffer, the CADDRE sites

will use a case cohort design in which the exposure

patterns of the ASD cases are compared to a random

sample of children living in the same geographic

area. A third study group, consisting of neurodevelopmentally

impaired children who do not have an ASD, will

round out the sample populations. The investigators

hope to enroll a total of 650 to 900 children,

aged 3 to 5 years, in each study group across

all the sites, making CADDRE the largest study

of its kind in the United States, says Newschaffer.

A uniform protocol across the sites will allow

the scientists to pool their data.

CADDRE will collect and archive blood, cheek cell, and hair samples

from the children in order to investigate a broad range of potential

risk factors. "We're not focused on the environment as much as CHARGE

is," says Newschaffer, "but we are collecting data on questionnaires

and reviewing medical records on exposure, in addition to the

biosampling for exposures. "

The scientists should have sufficient numbers

to look at gene–environment interactions. "We

are collecting DNA from the parents and the kids

from each of the groups. We'll have trio

data in each of the three groups, a potentially

powerful design," says Newschaffer.

CADDRE scientists will also characterize the

behavior of the children, as well as describe

any comorbid medical conditions and atypical

physical features. The goal is to sort out different

etiologic subgroups within the autism spectrum.

As Newschaffer explains, "There are a lot

of possible reasons why we've had a hard

time coming up with genetic and nongenetic risk

factors. One of them is that autism is likely

a heterogeneous condition, with different etiologies

producing kids with what appear to be similar

phenotypic profiles. If you don't separate

out the different etiologic groups, it's

going to be very hard to find an association

with a gene or an exposure. If we limit our analyses

to kids that have a certain profile, we're

going to be able to make some informed guesses

about what profiles might allow risk factors

to emerge," he says. The CADDRE sites will

begin recruiting children into the study in the

fall of 2006.

More Studies, More Acronyms

There are several other smaller epidemiological

studies in the works. In California, scientists

are tapping into specimen banks that have stored

blood samples taken from mothers during pregnancy

and from their children at birth. The Early Markers

for Autism (EMA) study employs a case–

control design, with about 100 children with an ASD (primarily autism), 100

who are developmentally delayed, and 200 from the general population. "We

can correlate what's happening in the mom and the baby, which is really

exciting," says Croen, a perinatal epidemiologist at the Kaiser

Permanente Division of Research in California and the project's principal

investigator.

EMA is a multidisciplinary collaboration with

epidemiologists, geneticists, immunologists,

neurovirologists, and endocrinologists, according

to Croen. "Because autism is so complex,

it's important for all these researchers

to communicate with each other. I think EMA is

a model for how to do research in autism," she

says. EMA is unique, according to Croen, because

the study will be looking for biological markers

of ASDs very early in development, during gestation,

and at birth. "This allows us to focus

on mechanisms that may be leading to autism rather

than mechanisms that are consequences of having

autism," she says.

The EMA scientists are investigating genetic and nongenetic factors,

with a focus on the immune dysregulation hypothesis of ASDs. "We're

measuring different kinds of immune markers, including immunoglobulin

levels and antibodies to specific infectious agents, cytokines, and

autoantibodies," says Croen. "We're looking for things that distinguish

kids who are subsequently diagnosed with autism from those who aren't.

This will help us understand the pathobiology of autism—the mechanisms

that are leading to the dysregulation in development. "

The three-year EMA is currently in its last year. "We still have lots

of analyses to do," says Croen, "but we're beginning to write some

papers. We're finding differences between the children in levels of

certain proteins measured in the circulating blood collected from

mothers during pregnancy. I think the study has much to contribute to

our understanding of the biology of what might be going wrong. "

Croen is also an investigator on the California

Autism Twin Study (CATS), which expects to recruit

300 identical and fraternal twin pairs born between

1987 and 1999 in which at least one of the twins

has an ASD. Comparing the twin pairs will allow

the scientists to estimate the heritability of

ASDs—the relative genetic and environmental

contributions to the disorder. "Knowing

the behavioral and developmental differences

between the twins might help us understand the

effects of gene expression, the in utero environment,

and environmental triggers," Croen says.

Hertz-Picciotto is also excited about a five-year

study that she and her colleagues hope to begin

soon. Unlike CHARGE, the new effort, called MARBLES

(Markers for Autism Risk in Babies—Learning

Early Signs), will be a prospective study in

which data will be gathered before the children

are diagnosed. Pregnant women who already have

at least one child with autism will be enrolled

right at the beginning of pregnancy. The mothers

will keep diaries about their symptoms and health-related

events, and the researchers will collect cord

blood samples and placentas.

Based on previous research, Hertz-Picciotto

expects that about 1 in 10 siblings of the autistic

children will also have the disorder, and perhaps

1 in 4 or 5 will be "on spectrum" with

a related but less severe condition such as Asperger

syndrome, or with some symptoms of the broad

behavioral phenotype, such as language delays

and atypical social skills. "This work

is complementary to the case–control approach,

and should provide us with a lot of information

that will build on what we find in CHARGE. It

should be a phenomenal resource," she says.

You Say You Want a Revolution

In April 2004, the U.S. DHHS issued a publication, Congressional

Appropriations Committee Report on the State

of Autism Research, describing recommendations

made by a panel of expert scientists convened

by the Interagency Autism Coordinating Committee

(IACC). The IACC panel suggested an ambitious

agenda, which included the goal of identifying

environmental risk factors and their associated

developmental windows within a four- to six-year

period, as well as identifying genetic and

nongenetic causes of ASDs and their interactions

within seven to ten years.

Hertz-Picciotto, a member of the IACC panel,

thinks these goals should be taken with a grain

of salt. "I'm optimistic that we

will have identified some environmental risk

factors, and may have excluded a few others,

between 2008 and 2010—but by no means will

we have the final word. The genetics and the

gene–environment interactions may be even

tougher. Unfortunately, I don't see enough

groups working on the environmental contribution

to autism, so it may be slower than projected," she

says.

Mark Blaxill, vice president of SafeMinds, a parent-led advocacy group,

also believes that environmental risk factors don't receive enough

consideration. "The CDC has not addressed the crisis in autism

responsibly," he says. "They should be raising the alarm, and they have

failed to do so. They should be asking why so many children are sick.

Instead, they've tried to suggest a degree of doubt about the

increases, and that diverts attention and funding from environmental

causes. "

Schendel responds, "It is clear that more children than ever before are

being classified as having an ASD. It is important that we treat common

developmental disorders, and especially the ASDs, as conditions of

urgent public health concern. The CDC's efforts in addressing this

public health concern include funding for ASD monitoring programs to

understand ASD trends, funding for research into the genetic and

environmental causes of ASDs, and education and outreach programs to

promote early identification and timely intervention for all children

with developmental problems. "

Despite the promise of the new epidemiological

studies, some researchers are still dismayed,

as one scientist put it, that "geneticists

are running the show, and ignoring the environmental

aspects." What would it take for things

to change? Blaxill invokes the ideas of philosopher

Kuhn, who suggested that scientific revolutions

occur when an old paradigm is replaced by a new

one. "I believe we're in the middle

of a paradigm shift," Blaxill says. "The

dramatic explosion of autism rates does not fit

the genetic model. It's an anomaly that

will kill the old paradigm."

Szpir