Developmental deficits Autism

This chapter is concerned with the neurochemical basis of developmental disability which is considered here in two forms the globally delayed or halted development seen in mental retardation, and the more circumscribed pattern of disordered development of autism. A range of deficits of important key aspects of consciousness are apparent in both conditions. Of particular relevance to consciousness are the cognitive and behavioural impairments in attention, concentration, memory, information processing and social behaviour which are commonly present. Consideration of aberrant neurotransmitter activities in these developmental deficits may provide insights into the role of neurotransmitters in consciousness. 

The developmental neurotoxicity guideline, accepted by OECD in 2007, has added the important aspect of behavioral effects of pre- and postnatal exposure to chemicals. This development arose from the notion that behavioral disorders in man such as anxiety, depression, phobias, autism, and attention deficit hyperactivity disorder, which appear to show increasing prevalences in western societies, may have a perinatal origin (4, 5). In the absence of causal inferences with respect to chemicals it seems nevertheless prudent to assess in a risk assessment whether such causal relations may exist. 

Autism is a developmental disorder of early childhood, characterized by social impairment, communication deficits, and compulsive behavior. The diagnostic criteria, epidemiology, and treatment of this disorder are covered elsewhere in this book (see chapter 42). This section focuses primarily on the dimension of social impairment and the neurobiology relevant to this aspect of autism. 

A potential limitation of most of the controlled studies discussed above relates to the numerous exclusion criteria used for patient selection. For example, in order to find homogenous samples, major depression, bipolar disorder, Tourette s disorder, psychosis (clomipramine, fluvoxamine and fluoxetine trials), primary psychiatric disorder other than OCD (clomipramine and sertraline trials), and attention deficit/hyperactivity disorder (ADHD), autism, or other developmental disorders (clomipramine and fluoxetine trials) were excluded. Thus it remains unknown how well these controlled studies will generalize to more naturalistic clinical populations that are highly comorbid and where exclusion criteria are not applied. 

Neuroleptic drugs have been prescribed for children in the treatment of psychotic disorders, Tourette s syndrome, attention deficit disorder, hyperactivity, behavioral and psychiatric complications of mental retardation, and pervasive developmental disorders, for example infantile autism (580,581). 

It is often difficult to ascribe neurodevelopmental deficits to chemical exposure only. Genetic makeup predisposes some individuals to chemical insult effects. Autism and ADHD are two prominent examples of developmental conditions that fit such a hypothesis. Both affect large numbers of children and their prevalences can be linked to environmental chemical exposures. These are discussed in the following chapters. 

The developing human brain is much more susceptible to injury caused by toxic agents than the brain of an adult. Probably all potential neurotoxic compounds would also cause damage to the developing brain and at much lower doses [1], Indeed, neuro-developmental disorders in children such as attention deficit, mental retardation or autism are often associated with the exposure to chemicals in the environment during early fetal and postnatal development [1-3]. 

Autism—(or other pervasive developmental disorder such as Asperger s syndrome) characterized by severe deficits in social interactions, language, and/or thinking or ability to learn, and usually diagnosed... 

In Part II, we consider some of the postnatal costs of those influences and examine the strong evidence that the prenatal environment is related to various behavioral dysfunctions or anomalies and to deficits in intelligence. The chapters in this part cover fetal alcohol disorders, transsexuality, developmental disabilities such as attention deficit hyperactivity disorder (ADHD), autism, and psychosis, as well as the emotional frameworks that give rise to a few other mental disorders. The important question of individual IQ is also addressed, including the controversies about its measurement in IQ tests (what are such tests Do their scores signify anything How is their reputed significance used ) and the extent to which the prenatal environment comes into play in the variance of IQ. 

I will focus in this chapter on major neuropsychological developmental disabilities that may involve a prenatal environmental impact cerebral palsy, epilepsy, vision and hearing deficits, speech deficits and learning disabilities, ADHD, and, in greater detail, autism. Childhood emotional or behavioral problems will be discussed in a later chapter. Mental retardation and growth delay are discussed in the book in various places. 

Since 1990, unprecedented numbers of children and adolescents have been diagnosed with serious mental iUness. These illnesses include attention deficit and hyperactivity disorders, autism, and bipolar disorder. For example, from 1994-1995 to 2002-2003, the rate of doctor s office visits for bipolar disorder among youth increased from 25 per 100,000 youths to 1,003. In addition, autism has become the fastest-growing developmental disability in the United States. 

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