Aetiology

Early interest centred on the possibility that experiential factors might somehow cause autism, but a host of research findings suggests that this is not the case. Rather, a fundamental disturbance in the central nervous system is implicated. At the same time important aspects of psychological development in autism have been investigated.

Psychological factors

Disabilities affecting attentional mechanisms, arousal, sensory deficits, memory management, and complex information processing, among others, have been proposed as primary deficits underlying the social impairment in autism. Although each of these helps us understand some aspects of the condition, none has, as yet, provided a more comprehensive account of the condition as a whole. (41

Among the most influential recent theories attempting to do that is the hypothesis that posits a lack of a central drive for coherence in children with autism, with the consequent focus on dissociated fragments of their environment rather than integrated 'wholes', leading to a fragmentary and overly concrete experience of the world.(42) Another cognitive account of autism posits that the commonly found difficulties in abstracting rules, inhibiting irrelevant responses, shifting attention, and profiting from feedback as well as in maintaining 'on-line' different pieces of information while a decision is made—the so-called 'executive functions'—underlie the social, communicative, and behavioural disabilities in autism. (43) Although both these theories—'weak central coherence' and 'executive dysfunction'—provide insightful new views of well-known clinical phenomena, neither phenomena can be seen as specific to autism (that is, relative to other developmental disorders) as the pervasive social impairment.

Probably the most influential current cognitive hypothesis focuses on mechanisms directly impacting on social understanding. This view, called the 'theory of mind' hypothesis, posits that autism is caused by the child's inability to attribute mental states such as beliefs and intentions to others. Devoid of this ability, individuals with autism are thought to be unable to infer the thoughts and motivations of others, thus failing to predict their behaviour and adjust their own actions accordingly, which results in a lack of reciprocity in communication and social contact.(44) Although more than 30 studies have documented such deficits in autism, there are still many limitations to this hypothesis. For example, more able individuals with autism can provide detailed accounts of other people's intentions, beliefs, and feelings—i.e. they exhibit 'theory of mind' skills—and yet may be totally unable to utilize these capacity in their spontaneous social adjustment. Such phenomena suggest that factors other than a cognitive understanding of mental phenomena are required for a person to meet the demands of everyday social life.

Researchers are now proposing more integrative theories capturing the synergistic nature of social-affective, motivational, and cognitive mechanisms facilitating socialization.(45) Of great interest in the past few years has been the confluence of experimental psychological paradigms and functional neuroimaging studies focusing on the same constructs. This new trend is leading to new insights into brain systems subserving basic social mechanisms such as gaze behaviour, social-affective responses, and thinking about other people's intentions and beliefs, (46) all of which are greatly compromised in autism.

Biological factors

The importance of biological factors in the pathogenesis of autism is suggested by its association with mental retardation and seizure disorder, other medical conditions, and the role of genetic factors. (8,47) Individuals with autism are at increased risk for developing seizures throughout childhood and adolescence. (4 48) Various non-specific neurological signs and symptoms may also be observed.

Autism has been associated with a host of medical conditions; but the absence of population data and rigorous diagnostic assessment makes such associations difficult to interpret. For example, early reports suggested an association with congenital rubella, but this now seems questionable given the diagnostic dilemmas and the observation that 'autistic-like' features diminish over time.(49) Gillberg(50) argues that medical conditions may be associated with autism in as many as one-third of cases, but Rutter et al.'(51) suggest that a more reasonable figure would be roughly 10 per cent of all cases. The strongest associations are with fragile X syndrome and tuberous sclerosis—both conditions having a strong genetic component.

Fragile X syndrome is an X-linked mental retardation syndrome involving a mutation characterized by a triplet repeat of cytosine- guanine-guanine (CGG) that may amplify with succeeding generations. It is associated with a characteristic facial appearance, enlarged testicles, mental retardation, and some autistic features. Early reports suggesting high rates of fragile X in autism have now been modified; fragile X affects perhaps 1 per cent of all individuals with autism. (52>

The autosomal dominant disorder tuberous sclerosis is characterized by abnormal tissue growth, or benign tumours (hamartomas), in the brain and in other organs. The condition, which may affect 1 in 10 000 individuals, is variably expressed; the phenotype ranges from minor skin problems or seizures to severe mental retardation with intractable seizures. The rate of this condition in autism (0.4-2.8 per cent) is significantly increased. (53) Fragile X syndrome and tuberous sclerosis are considered further in Ch§ptei..10...4..

The early impression that the role of genetic factors was limited has been modified given the association of autism with conditions like fragile X and tuberous sclerosis, and the results of twin and other family studies. Studies of monozygotic and dizygotic twins revealed higher levels of concordance for monozygotic twin pairs and elevations (relative to population rates) of autism in dizygotic twins as well. (8) General studies suggest that the recurrence risk of autism in siblings is in the order of 2 to 3 per cent—a 50- to 100-fold increase over the population rates. There also appear to be high rates of other developmental problems in siblings, raising the possibility that what is inherited may be a more general predisposition to developmental difficulties. Recent work also suggests elevated rates of anxiety and mood disorders in family members. However, specific modes of inheritance remain unclear. It now appears that several interacting genes are probably involved in the pathogenesis of autism. Efforts are underway to identify candidate genes and it is likely that some genetic forms of autism will be identified over the next few years. Although several studies have shown noted increased rates of pre-, peri-, and neonatal complications in children with autism, it is possible that some of these difficulties may reflect a genetic vulnerability in the child or that there may be an interaction of genetic and perinatal factors. (8)

Attempts have been made to identify neuropathological and neuroanatomical correlates of autism. Areas of interest have included the cortical areas responsible for language and social interaction (frontal and temporal lobes) as well as the neostriatum and cerebellum. (47) Interest in the cerebellums followed the report of reduced cerebellar size in the neocerebellar vermal lobules VI and VII; this observation has not proven readily replicable. Some individuals with autism have enlarged brains and head sizes, whereas others, particularly the more retarded, have smaller head sizes.(54) Neuropathological studies have suggested possible cellular changes in areas of the brain such as the hippocampus and amygdala.

Various neurotransmitter systems have been studied. Probably the most robust finding has been the observation that about one-third of children with autism have increased peripheral levels of serotonin. This finding is not specific to autism and its significance remains unclear. (55) Studies of other neurotransmitters such as dopamine produced inconsistent findings. The possible involvement of dopamine is suggested by the high levels of stereotyped behaviours in autism—behaviours which can be induced in animals by the administration of agents (stimulants) that affect levels of dopamine in the brain. Agents such as the neuroleptics, which block dopamine receptors, are effective in reducing the stereotyped and hyperactive behaviours of many autistic children. Another hypothesis has centred on the possible role of endogenous opioids, in that overproduction of such compounds might lead to social withdrawal and unusual sensitivities and behaviours. This has led to the administration of opioid antagonists such as naltrexone in autism; unfortunately results have been disappointing. Studies of the immune system in autism have been relatively uncommon and findings inconsistent.

Aspergers Answers Revealed

Aspergers Answers Revealed

Learn How to Help, Understand amp Cope with your Aspergers Child from a UK Chartered Educational Psychologist. Before beginning any practice relating to Aspergers it is highly recommended that you first obtain the consent and advice of a qualified health,education or social care professional.

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