BRIEF REPORT Brief Report: Asperger’s Syndrome and Sibling Birth Order Karmen Schmidt • Andrew Zimmerman • Margaret Bauman • Christine Ferrone • Jacob Venter • Jessaca Spybrook • Charles Henry Published online: 8 August 2012 Ó Springer Science+Business Media, LLC 2012 Abstract Prior investigations suggest that birth order position may be associated with the risk for developing a pervasive developmental disorder. This retrospective chart review examined the birth order status of 29 psychiatri- cally-referred patients with Asperger’s Syndrome (AS). Eighty-six percent of the subjects were first born. The finding was statistically significant when compared to an expected random distribution of AS subjects v 2 (1, N = 29) = 9.18, p \ 0.01. The reasons for such an asso- ciation are unclear though birth stoppage, obstetric com- plications, and immunological mechanisms may play a role. Keywords Asperger’s syndrome Á Pervasive developmental disorders Á Birth order Á Epidemiology Introduction Asperger’s Syndrome (AS) is categorized as a pervasive developmental disorder (PDD) in the Diagnostic and Sta- tistic Manual of Mental Disorders, Fourth Edition (DSM- IV) (American Psychiatric Association 2000). Patients with AS have impaired social interactions and restricted/rigid behavior patterns, but do not have the significant delays in language development seen in autism. Though the cause of AS is unknown, there is evidence supporting the role of genetics (Rehnstro ¨m et al. 2006; Salyakina et al. 2010). In addition, brain abnormalities have been reported in limbic, frontal, and parietal grey matter (Via et al. 2011) and in white matter microstructure (Bloemen et al. 2010). Currently, there is debate regarding the distinctness of the diagnosis of AS in comparison to autism, particularly with reference to the publication of the DSM-V (Happe ´ 2011). Some argue for the retention of the diagnosis given differences with autism in the type of social deficit, neurocognitive profile, and pattern of idiosyncratic interests (Ghaziuddin 2010). Birth order has been investigated as a clinical variable in a variety of neuropsychiatric conditions. Associations have been reported in schizophrenia (Gaughran et al. 2007), attention deficit hyperactivity disorder (ADHD) (Bhatia et al. 1991), and language impairments (Stanton-Chapman et al. 2002). Within the category of PDDs, there is evidence that autism is associated with first born children and children born much later in the sibling order (e.g. fourth birth posi- tion) (Deykin and MacMahon 1980; Durkin et al. 2008; Glasson et al. 2004; Lord et al. 1991; Piven et al. 1993; Tsai and Stewart 1983). The eldest child, in fact, may be at par- ticular risk (Croen et al. 2007; Durkin et al. 2008; Glasson et al. 2004). A recent meta-analysis supports risk specificity at the first birth position with the oldest being 61 % more likely to develop autism versus those born in the third K. Schmidt Á A. Zimmerman Á M. Bauman Á C. Ferrone Department of Pediatrics, Massachusetts General Hospital, Boston, MA, USA Present Address: J. Venter Department of Psychiatry, Cambridge Health Alliance, Cambridge, MA, USA J. Venter Á C. Henry Department of Psychiatry, Massachusetts General Hospital, Boston, MA, USA J. Spybrook Evaluation, Measurement, and Research Department, Western Michigan University, Kalamazoo, MI, USA C. Henry (&) The Lurie Center 1 Maguire Rd., Lexington, MA 02421, USA e-mail: charles_henry@hms.harvard.edu 123 J Autism Dev Disord (2013) 43:973–977 DOI 10.1007/s10803-012-1620-y