The risk is higher than previous estimates, and goes even higher if the second child is a boy. In fact, the risk rises to over 26% if the second child is male, and over 32% for infants with more than one older sibling with autism.
The Centre for Autism & developmental Disabilities Epidemiology (CADDE) at Johns Hopkins Bloomberg School of Public Health report, amongst other things, that there are 4 boys for every 1 girl with autistic disorder.
Scientists are working hard to narrow down the regions on chromosomes 7 and 15 to identify the specific gene(s) related to autism on these chromosomes. They are also expanding their searches to investigate other chromosomes for which there is preliminary suggestive evidence.
A report commissioned by Autism Advisory Board on Autism Spectrum Disorders notes that while there is considerable degree of variation in prevalence figures depending on the sources of data, using the Commonwealth Government’s Centrelink data, the core finding estimates the prevalence of autism spectrum disorders across Australia of 62.5 per 10,000 for 6-12 year old children. This means there is one child with an ASD on average in every 160 children in this age group which represents 10,625 children aged between 6 and 12 years with an ASD in Australia.
A similar study just released in the United States by the Centre for Disease Control and Prevention1, found a similar, although slightly higher prevalence of 1 in 150 [66.5 per 10,000] children among eight year olds. Researchers noted that this was consistent with previously published studies.