Autism prodrome 22 of 89
So, in relation to identifying the ASD prodrome, siblings studies are most
valuable when early developmental data is associated with outcome diagnoses, and
even then there may be some inaccuracies as these outcome data are reported for ages
2 and 3 years and may not include children who will fulfill criteria for diagnoses such
as Asperger syndrome only later on. Thus, in the context of our discussion of the
prodrome of ASD, we will limit our discussion to the few studies that report on early
development and markers as associated with a later diagnosis of an ASD.
To date, only four groups report on associations among early development
during the first year or two of life and later diagnoses of ASDs. Working in Canada,
Zwaigenbaum and his group were the first to publish longitudinal findings regarding
the early markers for ASD. Zwaigenbaum et al. (2005) examined the development of
high risk (SIBS-A) and low risk infants from 6 to 24 months and identified several
behavioral markers at 12 months (but not at 6 months) that predicted later diagnoses
of ASD at 24 months. The identified risk markers included atypical eye contact,
visual tracking, disengagement of visual attention, orienting to name, imitation, social
smiling, reactivity, social interest, and sensory-oriented behaviors. Siblings diagnosed
with ASD at 24 months also exhibited temperament characteristics of decreased
activity at 6 months, intense distress reactions and a tendency to fixate on objects at
12 months, as well as early language delays at 12 months. Mitchell et al. (2006) added
that siblings diagnosed with ASD at 24 months in this sample had delays in gestural
communication (i.e., giving, pointing, nodding head) as reported by their parents at 12
months. Bryson et al. (2007) documented a case series of 9 siblings from the previous
cohort who were followed prospectively from 6 months to 36 months, and who were
diagnosed with ASD between age 24 months and age 36 months. In this report, 2
subgroups of children with distinguishable early developmental profiles were