**9. Implications of genomic studies for clinical practice**

Genetic findings to date in autism include known genetic syndromes such as Rett and Fragile X; chromosomal structural variation such as duplications on ch15 and deletions on ch22 and increasing numbers of CNVs, many de novo, in a small proportion of cases, especially those with co-morbid developmental abnormalities. Common variants are only slowly emerging from genome-wide studies but sample sizes are still relatively modest compared to other dis‐ orders. The diagnosis remains as a clinical one, but genetic testing has diagnostic, prognostic and family planning implications, and in the coming years may also be of importance with respect to potential treatments for specific conditions such as Rett and Fragile X. Therefore, a clinical genetics evaluation should be considered in ASD children in order to identify syn‐ dromic forms of autism, identify familial cases, and drive diagnostic testing. Genetic testing using aCGH has been recommended by the American Academy of Pediatrics [101] and the American College of Medical Genetics [102, 103], particularly to evaluate aetiological hetero‐ geneity and identify syndromes. For the vast majority of cases with an identified genetic cause, there is no specific benefit in terms of treatment, but the diagnosis itself may be of value to parents seeking an explanation for the symptoms they see in their child. Acceptance of the disorder may be easier in the presence of a known cause as echoes of social causation and blame can still be heard. Family investigation may also be warranted, particularly where the proband has an identified genetic causation as recurrence risk in siblings may have implica‐ tions for family planning. If a genetic cause of pathogenic significance is identified, the recur‐ rence risk for sibs may be established according to the particular genetic diagnosis. In the majority of cases, no genetic alteration is found, and an empirical risk for siblings of 10-20% can be provided. Establishing a clear de novo origin for a given mutation may enable a low risk estimate in siblings although there are caveats relating to the exact origin of the mutation. Finally, and re-stating the main goal of genetic research in ASD, a better understanding of underlying biology may lead to novel and unexpected treatment possibilities. Early signs of this are emerging in human trials for treatments aimed at the specific mutations found in Rett and Fragile X syndromes.
