Autism spectrum disorders and autistic like traits: similar etiology in the extreme end and the normal variation.
BACKGROUND
Autism spectrum disorders (ASDs) have been suggested to represent the extreme end of a normal distribution of autistic like traits (ALTs). However, the evidence of this notion is inconclusive.


OBJECTIVE
To study whether there are similar genetic and/or environmental etiologies behind ASDs and ALTs.


METHODS
A nationwide twin study.


METHODS
Consenting parents of all Swedish twins aged 9 and 12 years, born between July 1, 1992, and December 31, 2001 (n = 19 208), were interviewed by telephone to screen for child psychiatric conditions, including ASDs.


METHODS
Two validated cutoffs for ASDs, 2 cutoffs encompassing the normal variation, and 1 continuous measure of ALTs were used with DeFries-Fulker extreme-end analyses and standard twin study methods.


RESULTS
We discerned a strong correlation between the 4 cutoffs and the full variation of ALTs. The correlation was primarily affected by genes. We also found that the heritability for the 4 cutoffs was similar.


CONCLUSIONS
We demonstrate an etiological similarity between ASDs and ALTs in the normal variation and, with results from previous studies, our data suggest that ASDs and ALTs are etiologically linked.
Department of Clinical Sciences, Lund University, Sweden. sebastian.lundstrom@neuro.gu.se
Sebastian
S
Lundström
Zheng
Z
Chang
Maria
M
Råstam
Christopher
C
Gillberg
Henrik
H
Larsson
Henrik
H
Anckarsäter
Paul
P
Lichtenstein
D002648:Child; D002659:Child Development Disorders, Pervasive / Q000453:epidemiology / Q000235:genetics* / Q000523:psychology*; D015331:Cohort Studies; D004200:Diseases in Twins / Q000235:genetics / Q000523:psychology; D005260:Female; D006306:Health Surveys; D006801:Humans; D007406:Interview, Psychological; D008297:Male; D013548:Sweden / Q000453:epidemiology; D014427:Twins / Q000235:genetics / Q000523:psychology