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Age of Autism Science Summary: Quantifying and modeling birth order effects in autism.

Science post imagePLoS One. 2011;6(10):e26418. Epub 2011 Oct 19.

Quantifying and modeling birth order effects in autism.

Turner T, Pihur V, Chakravarti A.


Center for Complex Disease Genomics, McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.


Autism is a complex genetic disorder with multiple etiologies whose molecular genetic basis is not fully understood. Although a number of rare mutations and dosage abnormalities are specific to autism, these explain no more than 10% of all cases. The high heritability of autism and low recurrence risk suggests multifactorial inheritance from numerous loci but other factors also intervene to modulate risk. In this study, we examine the effect of birth rank on disease risk which is not expected for purely hereditary genetic models.We analyzed the data from three publicly available autism family collections in the USA for potential birth order effects and studied the statistical properties of three tests to show that adequate power to detect these effects exist. We detect statistically significant, yet varying, patterns of birth order effects across these collections. In multiplex families, we identify V-shaped effects where middle births are at high risk; in simplex families, we demonstrate linear effects where risk increases with each additional birth. Moreover, the birth order effect is gender-dependent in the simplex collection. It is currently unknown whether these patterns arise from ascertainment biases or biological factors. Nevertheless, further investigation of parental age-dependent risks yields patterns similar to those observed and could potentially explain part of the increased risk. A search for genes considering these patterns is likely to increase statistical power and uncover novel molecular etiologies.

PMCID: PMC3198479

Free PMC Article



I am so tired of the time and resources wasted on these studies. I have four children ranging from age 16 down to 2 years old. I was 24 when my 16 year old was born and 39 when my 2 year old was born. My first born is the only one who has Autism. So fit me into your study. My 14 year old has some undiagnosed sensory issues and social anxiety. My 5 and 2 year olds are extremely social and developing at or above their age. They have never been on antibiotics and oh they have also never received a vaccine!


I keep wondering what someone like David Suzuki thinks about vaccines and thimerosal/aluminum etc. I mean that is some serious, directed polluting being done to our children.

Cherry Sperlin Misra

Breaks my heart to see the name "Chakravarti" as an author of this study. I just want to shake him and shout "Its the fish stupid". Now, Ill have to explain that- The name Chakravarti is a Bengali name and Bengalis in India often eat fish twice a day, seven days a week. The fish is highly contaminated with mercury and as a result, the rate of autism is very high among Bengalis. In fact, Bengalis apparently had autism in their population even during the days in India, when only three DPT vaccines with mercury were given to babies (as compared to 8 or 9 today). On the other hand we have, in India, a large population of Tamilian Brahmins who often do not eat even a bite of egg, let alone meat or fish in their lives. There may be some cases of autism among this population as a result of vaccines, but in about 15 years of watching autism in New Delhi, I have not seen a case so far. I also frequently see in my nursery school in Delhi, children who are not autistic, but who have some symptoms of autism that wane with time. I have not even seen this among the children of Tamilian Brahmins. As a result of this, I believe that the effect of mercury in fish on human beings, needs to be studied far more than it has been.


From the abstract:
"risk increases with each additional birth"

Later kids get more vaxes? Hmmm.


Quote from the abstract:

"In this study, we examine the effect of birth rank on disease risk which is not expected for purely hereditary genetic models" ...

"A search for genes considering these patterns is likely to increase statistical power and uncover novel molecular etiologies"

I may be missing something, but on the face of it, these statements contradict each other. Smells like the blinding power of dogma (again).

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