That was the primary finding reported by Neil Risch and colleagues* based at the University of California, San Francisco in the United States looking at the pattern of familial (sibling) recurrence of an autism spectrum disorder (ASD). Based on an examination of data held at the California Department of Developmental Services (DDS), an agency providing services and support for those with developmental disabilities, researchers were able to cross-link data with birth certificate records in order to determine how many siblings of children already diagnosed with ASD were themselves diagnosed with autism in comparison to brothers and sisters of an asymptomatic control group. The 10% estimated recurrence rate of autism in siblings mirrors other findings from other geographical locations based on similar database interrogation**.
Researchers also reported that birth order and the interval between births also seemed to exert some effect on the likelihood of siblings of children with autism presenting with similar issues. A short interbirth interval of less than 18 months for example, increased the recurrence risk up to 14% compared with an interval of 4 years or more between births (~7%). This may indicate that issues such as nutritional factors, as a consequence of the depletion of maternal micronutrients which accompanies pregnancy and birth, may play a role in moderating offspring autism risk as has been raised in other research.
Although not able to take into account issues such as reproductive stoppage – where couples purposefully make a decision not to have more children – the data from Risch and colleagues provides further information regarding the role that genetics (and/or epigenetics) plays in the onset of autism and may help in counselling families already touched by autism.
* Risch N. et al. Familial Recurrence of Autism Spectrum Disorder: Evaluating Genetic and Environmental Contributions. Am J Psychiatry. 2014 Jun 27
** Gunnes N. et al. Interpregnancy Interval and Risk of Autistic Disorder. Epidemiology. 2013 Nov;24(6):906-12.
Further discussion about this paper can be found at: http://questioning-answers.blogspot.com/2014/07/familial-recurrence-of-autism-spectrum-disorder-again.html