Hi steelerfan!
Before setting out to research your question, I spoke briefly with my
friend Jeff, who is in the throes of a PhD and MD course of study at
the University of Michigan Medical School. Who best to ask about
children than a future pediatrician?
Jeff explained that there was indeed a multitude of research
indicating some link to maternal age, and very nearly as much
indicating that other risk factors figure more highly into the
equation than advanced maternal age - where maternal age is viewed to
be a factor at all. He advised caution when reading the available
research, as it's a highly controversial subject in the medical
community. [Indeed. In the course of my research, I found a study
from the early '80s indicating a possible link between autism and
being born in March! - missy ] This controversy is mentioned
euphemistically in the National Library of Medicine's "Medline Plus
Medical Encyclopedia":
"In the past, autism was thought to be a mental illness caused by bad
parenting. This destructive idea has been disproved. We now know
autism to be a physical condition linked to abnormal biology and
neurochemistry in the brain. The exact causes of these abnormalities
remain unknown, but this is a very active area of research."
Autism - Causes and Risks
http://www.nlm.nih.gov/medlineplus/ency/article/001526.htm#causesAndRisk
According to the National Institute of Child Health and Human
Development:
"Autism is not a disease that you “get,” the same way you can get the
flu. Instead, scientists think autism has its beginnings before a
person is even born. No one knows the exact cause or causes of autism,
but scientists have some theories."
Why do some people get autism?
http://www.nichd.nih.gov/publications/pubs/autism/facts/sub3.htm
The page goes on to note that a group of scientists is currently
working on discovering *genetic* causes for autism, suspecting an
error in genes as the main cause of autism. They are trying to
determine what might be causing this error. It appears that this is
being viewed as the research closest to finding the actual cause of
autism, as seen on the National Institute of Mental Health's
"Unraveling Autism" page:
"While it is known that heredity plays a major role in complex
disorders like autism, the identification of specific genes that
confer vulnerability to such disorders has proven extremely difficult.
Once autism-linked genes are identified, however, scientists will
bring to bear sophisticated research tools to find out what activates
them, what brain components they code for, and how they affect
behavior. The prospect of acquiring such molecular knowledge holds
great hope for the engineering of new therapies.
Evidence suggests that unaffected family members may share with their
ill relatives genes that predispose for milder behavioral
characteristics that are qualitatively similar to those of autism.
For example, some relatives of people with autism may have mild
social, language, or reading problems. Family members also may share
telltale neurochemical signatures that may be implicated in the
disorder. Researchers are studying such families to characterize these
behavioral and biological traits, in hopes of tracing the variations
in the genetic blueprint that contribute to autism."
Unraveling Autism - NIMH
http://www.nimh.nih.gov/publicat/unravel.cfm
Similarly, the National Institute of Neurological Disorders and Stroke
appears to be concentrating on possible genetic causes, and does not
mention maternal age at all:
" Recent studies strongly suggest that some people have a genetic
predisposition to autism. Scientists estimate that, in families with
one autistic child, the risk of having a second child with the
disorder is approximately five percent, or one in 20, which is greater
than the risk for the general population (see "What is autism?").
Researchers are looking for clues about which genes contribute to this
increased susceptibility. In some cases, parents and other relatives
of an autistic person show mild social, communicative, or repetitive
behaviors that allow them to function normally but appear linked to
autism. Evidence also suggests that some affective, or emotional,
disorders occur more frequently than average in families of people
with autism. "
What Role Does Genetics Play? - Autism Fact Sheet
http://www.ninds.nih.gov/health_and_medical/pubs/autism.htm#genetics
A press release from November, 2000 indicated that scientists had
identified at least one gene which appears to be linked to autism in a
large number of cases:
"Researchers funded by the National Institutes of Health have
identified a gene that may predispose people to developing autism. The
gene, known as HOXA1, plays a crucial role in early brain development.
The study was conducted by a research team in NIH's Collaborative
Programs of Excellence in Autism and was published in the December
issue of Teratology.
"These findings strongly suggest that a gene controlling early brain
formation may underlie the development of autism in a large number of
cases," said Duane Alexander, M.D., Director of the National Institute
of Child Health and Human Development (NICHD) and chair of NIH's
autism coordinating committee."
Researchers Identify Gene Common to Many Autism Cases
http://www.nichd.nih.gov/new/releases/autism.cfm
In 2001, researchers identified another gene linked to autism:
"Scientists funded by the National Institute of Mental Health have
linked a gene that may influence human brain development with autism
susceptibility. They pinpointed the candidate gene, WNT2, in a region
of chromosome 7 suggested by several studies over the past few years.
NIMH grantees Thomas Wassink, M.D., University of Iowa, and Joseph
Piven, M.D., University of North Carolina, and colleagues, report on
their findings in the American Journal of Medical Genetics, available
online May 17, 2001."
Brain Gene Implicated in Autism
http://www.nih.gov/news/pr/may2001/nimh-17.htm
The scientific and medical juries are still out on this subject - no
studies definitively linking maternal age to autism are currently
available, only those that mention it as a *possible* link or conclude
that it is not linked at all. While research in the early to
mid-1980s pointed to a connection between maternal age and autism,
currently accepted theories indicate that genetics play a significant
role in ocurrences of autism. Please keep this in mind as you go
through the studies I've found for you.
I searched the National Library of Medicine's PubMed for abstracts to
studies discussing advanced maternal age and autism (in some cases
linking them only very tenuously, and some concluding that maternal
age is not the sole cause), then sought additional information via
Google. In many cases, the actual studies are not available online,
but you may be able to get to them if you have access to medical
journals through your local university or public library. The PubMed
abstracts also include e-mail contact information for the researchers
responsible for each study. I will quote briefly from each abstract
and/or additional article, and provide citations for each.
-------------
Key to Journal Names in Citations:
J Autism Dev Disord. = Journal of Autism and Developmental Disorders
J Dev Behav Pediatr. = Journal of Developmental and Behavioral
Pediatrics
J Perinat Med. = Journal of Perinatal Medicine
year;volume(issue): page numbers
-------------
"In a total population survey of childhood psychosis in the region of
Goteborg, 20 children (2 in every 10,000) fulfilled the diagnostic
criteria for infantile autism formulated by Rutter. There was a male
preponderance with 15 boys and 5 girls. Eighty-five percent of the
mothers were older than average."
Gillberg C.
Maternal age and infantile autism.
J Autism Dev Disord. 1980 Sep;10(3):293-7.
PMID: 6927656 [PubMed - indexed for MEDLINE]
http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=6927656&dopt=Abstract
"From a live birth population of more than 3.5 million, 4381 children
with autism were identified. Increased risks were observed for males,
multiple births, and children born to black mothers. Risk increased as
maternal age and maternal education increased."
Croen LA, Grether JK, Selvin S.
Descriptive epidemiology of autism in a California population:
Who is at risk?
J Autism Dev Disord. 2002 Jun;32(3):217-24.
PMID: 12108623 [PubMed - in process]
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12108623&dopt=Abstract
"Are there other studies with similar results?
Our finding that autism is much more common in boys than girls is
consistent with the vast majority of previous studies. Maternal age
and social class have been the subject of numerous investigations.
Our finding of an increased risk with increasing maternal age and
education level is consistent with some studies but not with others.
There have been very few studies that have investigated such factors
as twinning, racial variation, and immigrant status in relation to
risk of autism, and the results of these have been inconsistent as
well. Our study is the first to examine all of these characteristics
in the same population. Only further research can resolve these
inconsistencies."
Media Messages:
Descriptive Epidemiology of Autism in a California Population:
Who Is at Risk?
Lisa A. Croen, PhD, Judith K. Grether, PhD, Steve Selvin, PhD
http://www.dhs.cahwnet.gov/ehib/EHIB2/topics/Descriptive_autism_QA.htm
"Birth orders and maternal ages of the 113 autistic patients were
compared with those of the general population. An excess of mothers
aged 35 or older was observed in the autistic group, though the mean
maternal age for the whole group was very similar to those of the
general population. A deviation from average in birth order was
observed in autistics. Significantly more autistics were products of
at-risk pregnancies (defined as either first, fourth, or later born,
or born to mothers aged 30 or older) than the base population."
Tsai LY, Stewart MA.
Etiological implication of maternal age and birth order in infantile
autism.
J Autism Dev Disord. 1983 Mar;13(1):57-65.
PMID: 6853439 [PubMed - indexed for MEDLINE]
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=6853439&dopt=Abstract
"It is concluded that uncontrolled social class factors might account
for raised maternal age in middle class mothers of autistic children
found in other studies."
Steinhausen HC, Gobel D, Breinlinger M, Wohlleben B.
Maternal age and autistic children.
J Dev Behav Pediatr. 1984 Dec;5(6):343-5.
PMID: 6511933 [PubMed - indexed for MEDLINE]
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=6511933&dopt=Abstract
Interestingly, this study indicates that advanced *paternal* age may
increase the risk of autism:
"Increasing father's age was associated with increased risk of
autism."
Burd L, Severud R, Kerbeshian J, Klug MG.
Prenatal and perinatal risk factors for autism.
J Perinat Med. 1999;27(6):441-50.
PMID: 10732302 [PubMed - indexed for MEDLINE]
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10732302&dopt=Abstract
From information available, it would appear that advanced maternal age
is not strongly indicative of an autism risk, but merely a possibile
link. As with any such subject, if you feel you need more information
or a full explanation of risk factors, please do consult a physician.
For further studies, current research news and breakthroughs, and
autism resources, the National Library of Medicine's Medline Plus
Autism Page is frequently updated:
MedlinePlus Health Information - Autism
http://www.nlm.nih.gov/medlineplus/autism.html
If any part of my answer is unclear, please don't hesitate to ask for
clarification. I will be happy to assist you further.
--Missy
Search terms were: [ autism "maternal age" ] at Medline, MedlinePlus,
NIMH, PubMed, and on Google. |
