Some children with autistic siblings have no problems, some have minor problems, and some have significant problems. In 2003, Hastings studied the effect of an autistic sibling based on their mothers" answers on questionnaires. He wanted to know if the handicapped sibling had an effect and whether the effect was different depending on the age, sex, closeness in age, maternal stress, or where the sibling lived (some lived in special care residences). These questions were all included in the questionnaire. Results showed that the normal siblings are at an increased risk of poor psychological adjustment when compared to children who have no handicapped siblings. (Hastings, 2003) There were also siblings found who would probably benefit from psychological help for other minor developmental abnormalities. .
It is hard to know, however, if the reason for this is poor adjustment or the extended phenotype of autism to 1st degree relatives. Autism is, after all, known to have genetic links. The reason for its rarity is because most autistic children will never go on to reproduce, and many parents stop having children after having an autistic child. However, some parents already have children, and some continue to have children despite their elder handicapped child. This is why Hughes chose to test for executive functioning and spatial span in the normal siblings. She wanted to see if these genetic links affected the apparently normal children. In this particular study, doctors compared the spatial working memory and executive control of autism siblings, developmental delay siblings, and siblings of normal children. They concluded that poor executive control was characteristic of a subset of autism siblings rather than a general phenomenon. When they tested for executive function tasks, however, significantly more autism siblings experienced difficulty. This would suggest that executive dysfunction is in the broad phenotype of autism that can affect siblings.