|Sister. So you have a twin sister... @ Wikipedia|
Cross-linking data derived from "California Department of Developmental Services records with state birth certificates" authors set about identifying "all siblings and half siblings of individuals affected with ASD born between 1990 and 2003". They looked at subsequent births "born after ASD [autism spectrum disorder] index cases" and compared them with control participant data for a diagnosis of ASD.
The value-added bit to the Risch data is that alongside looking at birth order and any effect on risk of ASD - second born children in autism cases were found to be at greater risk than later born siblings (11.5% vs. 7.3% respectively) of subsequent diagnosis - the authors also looked at the issue of inter-birth interval and whether that exerted any effect. It did as it happens: "the recurrence risk reaching 14.4% for an interbirth interval of 18 months or less, compared with 6.8% for an interval of 4 years or more". This issue under the name inter-pregnancy interval (IPI) is something which has also graced this blog on a previous occasion (see here) with autism in mind. On that previous post, I covered some of the possible hows and whys when it comes to a short IPI and autism risk...
There is little more for me to say about the Risch paper and what it means for something like genetic counselling when it comes to autism risk. I should point out that not every piece of research on this topic has arrived at the same figure (see here and see here for example) but one can perhaps see how variables such as geography and gender might affect recurrence risk. I will also drop in the paper by Hoffmann and colleagues  (yes, the same authorship team) on reproductive stoppage as also being relevant at this point covered in a previous post (see here).
Music to close.... Anything Goes (Indiana Jones style).
 Risch N. et al. Familial Recurrence of Autism Spectrum Disorder: Evaluating Genetic and Environmental Contributions. Am J Psychiatry. 2014 Jun 27. doi: 10.1176/appi.ajp.2014.13101359.
 Sandin S. et al. The Familial Risk of Autism. JAMA 2014; 311: 1770-1777.
 Hoffmann TJ. et al. Evidence of Reproductive Stoppage in Families With Autism Spectrum Disorder: A Large, Population-Based Cohort Study. JAMA Psychiatry. 2014 Jun 18. doi: 10.1001/jamapsychiatry.2014.420.
Risch, N., Hoffmann, T., Anderson, M., Croen, L., Grether, J., & Windham, G. (2014). Familial Recurrence of Autism Spectrum Disorder: Evaluating Genetic and Environmental Contributions American Journal of Psychiatry DOI: 10.1176/appi.ajp.2014.13101359