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Prospective studies of infant siblings at risk of autism

Kristi Poppi - September 20th 2016

A recent review by Szatmari et al (2016) has looked at the latest research on high risk (HR) infant siblings and highlighted areas that need to be further explored.

Over the last decade there has been a growing interest in the younger siblings of children with autism, as various studies have shown that these siblings are at higher risk of developing this disorder. The aim in studying these HR siblings is to gain a better understanding of the genetic and environmental components of ASD and to discover possible early markers.

Szatmari’s review included studies of younger siblings of a child with ASD, who are usually followed longitudinally with routine evaluations from the first year of postnatal life until they are 36 months. It is at that age that a diagnosis of ASD is considered more stable and reliable. The HR siblings that are eventually diagnosed with an ASD can then be compared with HR siblings that are not affected and with low-risk children, where there is no family history of autism. The aim is to generate new information about the manifestation of autism and to determine any early symptoms.

The review noted some key findings that emerged from the HR infant sibling studies. These findings fell into three areas: 
  • Early behavioural markers of ASD
  • Recurrence risk estimates for the development of ASD in HR siblings
  • Areas of further interest

Early behavioural markers

The studies included in the review suggest that about 40% of siblings eventually confirmed with ASD had become symptomatic by the age of 18 months and that the stability of this early diagnosis was very high (93%). The review also found a marked heterogeneity in these early symptoms, which can make an early diagnosis more difficult. Nonetheless, two combinations of features seemed most predictive of ASD:

  • Poor eye contact along with lack of non-verbal communication skills and limited use of giving objects to share.
  • Intact eye contact with emerging repetitive behaviours, along with a lack of the ability to share and to request objects. 

Infants with either of these two combinations of features had a rate of ASD diagnosis that was three times greater than those without, an important consideration when monitoring children at high risk.

In considering early ASD symptoms, the review authors also noted the diversity of onset patterns across time and core areas of impairment. For example, it seems that the greater the cognitive impairment, the earlier the age of autism onset. For this reason they suggest that it could be more advantageous to evaluate an infant’s developmental trajectory, instead of assessing various cross-sectional markers at various time points.

Recurrence risk

The authors go on to consider the evidence regarding the risk that an HR sibling may go on to receive a diagnosis of an ASD. Whilst previous estimates of this risk were between 3-10%, more recent studies put this estimate considerably higher, at between 10-20%. The risk seems higher for boys, although the gender of the older child was not a factor, and higher where there is more than one older sibling diagnosed with an ASD.

Areas of further interest

Finally, the study authors underline three emerging areas of interest where further findings could be of significant clinical and academic importance.

  • There is a growing interest in neurobehavioral and neurophysiological indices of attentional processing and atypical brain development in infancy. If established, these indices may lead to a more distinctive separation of affected and unaffected individuals.
  • There are a significant number of HR siblings who while not going on to receive a diagnosis of autism, nonetheless face other significant developmental challenges. More research may identify ways to monitor and support those HR children who do not cross a diagnostic threshold for an ASD.
  • Finally, the authors note work that is underway to evaluate whether or not early intervention could benefit these siblings who are at risk of ASD or of another developmental challenge.

One of the main objectives of research in this area is to develop screening tools that can be used at a very young age in order to facilitate early intervention. The authors emphasize the importance of conducting more studies, including randomized controlled trials, to evaluate the impact of screening and to gain a better understanding of developmental trajectories before the age of 12 months.

References

Szatmari P, Chawarska K, Dawson G, Georgiades S, Landa R, Lord C, Messinger DS, Thurm A, Halladay A. (2016). Prospective Longitudinal Studies of Infant Siblings of Children With Autism: Lessons Learned and Future Directions. J Am Acad Child Adolesc Psychiatry. 55(3):179-87.


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Welcome to ourNews, where we keep up-to-date with research and other news related to infant mental health. These articles can be of interest to both parents and professionals.
We are keen to know your views and so please do comment on our articles.
Is there a topic that you would like us to write about? Just send us a message via 'Contact us'.

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