Early Detection of Autism in Infants and Toddlers (Part 3)
These animal subjects subsequently displayed the persistent and severe cognitive and social impairments as well as stereotyped and self-stimulatory behaviors that are defining features of autism (Dawson et al. 1998). However, this discovery does contrast a recent case study evaluation of a young autistic girl by Dawson, Osterling, Meltzoff, and Kuhl which determined that in this specific child at one year of age, impairments did not exist in the domains of immediate memory of actions, working memory, and response inhibition linked to frontal lobe functioning as core features of autism (2000).
Head Circumference Growth as a Predictor of Autism
A recent discovery in human physiology and brain development research has led to the involvement of the Baby Sibs consortium in an effort to determine the earliest physical markers of autism, particularly abnormal head circumference growth (Kalb, 2005). It is presumed that if a significant increase in head growth during infancy is a risk factor for autism, the mechanism that triggers this onset of growth would actually precede any manifestation of the disorder. Post-mortem brain studies described by Lainhart suggest that brain abnormalities begin before birth in at least a percentage of cases of autism, and therefore, provide further evidence to this claim (2003). According to this same author, between birth and six to fourteen months of age, head circumference has been shown to increase at a significantly greater rate in children with autism than in an control or reference sample (Lainhart, 2003); fifty-nine percent of children with autism and only six percent of typically developing children show an increase of two or more standard deviations in head circumference during this developmental time. In another study of this same type with consistently similar results, it was determined that approximately ninety percent of two and three year old children had brain volumes larger than the healthy average in addition to abnormally large head circumferences (Courchesne, Carper, & Akshoomoff, 2003). In comparison to growth charts produced by the Center for Disease Control, average head size in recruited participants increased from the twenty-fifth percentile at birth to the eighty-four percentile in six to fourteen month old babies with autism spectrum disorders (Courchesne, et al. 2003), well before the typical onset of clinically significant behavioral symptoms. By late childhood, however, a follow-up study of participants between the ages of eight and forty-six yielded MRI results demonstrating that this extreme brain overgrowth is time limited and that eventually brain size between control and autistic individuals becomes approximately equal (Courchesne, et al. 2003). An additional study by Torrey, Dhavale, Lawlor, and Yolken discovered a pattern of significantly larger body weight and length in four month old infants later diagnosed with autism in comparison to control subjects, inferring that an abnormality in metabolism, growth factors, and hormone levels may indeed be the culprit (2004). Accelerated rate in head circumference growth is associated during infancy with overall increased brain volume and gray matter, as well as increased cerebral gray matter. Scientists have not come to a conclusive decision as to what exactly accounts for this increase, but theory suggests that the sudden growth could result from an over abundance of neuronal connections, which pruning fails to eliminate (Kalb, 2005).
The discovery that an overgrowth of head circumference occurs frequently during the early months of life for those later diagnosed with autism holds a very promising clinical role in the detection of this disorder. An inexpensive and noninvasive assessment technique, the tracking of brain size development may be a key to early diagnosis and consequently, even earlier intervention practices. If these results are further confirmed by subsequent studies, physicians and psychologists in the future may be able to quickly assess the risk for developing autism based on physical examination alone.
Communication Abnormalities: Nonverbal Gestures and Speech
Parents frequently express initial concern over their child’s speech and communication development, and thus this often becomes the first complaint of autism-related behavior that sends parents to seek out an evaluation. Although typically developing newborn infants possess immature brains, limited cognition, and weak bodies, it has been established that most are very motivated beyond an instinctual drive to attract parental care for immediate biological needs, and thus “to communicate intricately with the expressive forms and rhythms of interest and feeling displayed by other humans,” (Trevarthen & Aitken, 2001). This drive does not seem to be as strong in young children with autism as in most instances they communicate less frequently than matched developmentally delayed children. These children are also less likely to use contact and conventional gestures in requesting an object, but are, in fact, more likely to use unconventional gestures to make up for this deficit in such ways as manipulating the hand of the individual with whom they are interacting to the desired object (Volkmar et al. 2005). In an article by Werner et al. it was demonstrated that at two months of age, infants start to implement their vocalizations in a semi-social manner, and this distinction further aids in subsequent speech and language development (2000). From these results, one can determine that perhaps differences in these areas of vocalization between typically developing and impaired infants become evident by the age of twelve months. Also between the ages of six months to one year, meaningful differences become more pronounced in the communicative criteria, especially noted when these children develop a general lack of orientation toward verbalization and their own names. These differences, however, are often not utilized in evaluation of development and assessment for autism in individual children because most parents fail to recognize these communication difficulties until spoken language is more apparently delayed.
Within this same realm of communicative impairment, very young children with autism have also be distinguished in various studies from typically developing controls on the basis of response to name calling.