Half of Aspergers children have ASD in paternal family history

Half of boys with asperger syndrome have a paternal family history of ASD.

Entrez PubMed J Autism Dev Disord. 2005 Apr;35(2):159-66.
Asperger syndrome: familial and pre- and perinatal factors.
Gillberg C, Cederlund M.
Department of Child and Adolescent Psychiatry, University of Goteborg, Sweden. christopher.gillberg@pediat.gu.se

OBJECTIVE: Study familial and pre- and perinatal factors in Asperger Syndrome (AS). METHODS: One hundred boys with AS had their records reviewed. "Pathogenetic subgroups" were defined according to presence of medical syndromes/chromosomal abnormalities, indices of familiality, and pre- and perinatal risk factors predisposing to brain damage. RESULTS: No major index of pathogenetic factors was found in 13%, a syndrome/chromosomal abnormality in 8%, pre- or perinatal risk 13%, combined pre- or perinatal risk and family history in 11%, and family history only in 55%. COMMENT: About 50% of all boys with AS have a paternal family history of autism spectrum disorder. Pre- and perinatal risks appear to be important in about 25% of cases.

Why paternal only? Might be an artifact of males being more vulnerable to expressing the genetic foundation of the disorder, since the "father" is a large part of paternal history.