Causal association specificity

The subject of what evidence is necessary to conclude that an exposure is causally associated with disease has received much discussion over the years. In 1964, the seminal report to the Surgeon General on Smoking and Health [United States Department of Health, Education, and Welfare (DHEW 1964)] published criteia by which to evaluate whether an exposure was causally related to disease. These criteria were consistency, strength of association, specificity of the association, temporal relationship of the association, and coherence of the association. 

In this connection, a specific loss of hypoxanthine-quanine phosphoribosyltransferase activity has been observed in cases of gout associated with the overproduction of uric acid [305] and in a neurological disorder, the Lesch-Nyhan syndrome [306]. Although a causal relationship has not been established, these disorders could be indicative of the importance of these enzymes. 

This diversity of mental retardation, in both cause and phenotype, carries important implications for consideration of the biochemistry of consciousness. On the one hand, because this is an investigation of multiple causalities—including, for example, inborn errors of metabolism, each of which has its own unique biochemical profile (Cook Leventhal, 1996), it may not prove possible to identify specific neurotransmitter abnormalities which are common to mental retardation as such. On the other hand common themes concerning key neurotransmitters may be identified from studies of mental retardation. Altered neurotransmitter functioning associated with the severity of mental retardation is open to different interpretations, either reflecting fundamentally impaired development of cerebral structure or a more general impairment of central transmitter activity and functioning. 

If there is an association between the extent or severity of abnormal neurotransmitter functioning and the global measure of severity of autism, the direction and mechanism of causality may still be unclear (as has been discussed in mental retardation). However, neurotransmitter correlates of specific aspects of autism, such as social isolation or obsessional behaviour, are likely to be more revealing and of greater relevance to the study of consciousness. 

Although a carcinogen may act upon more than one target, the specificity of an association (an increased occurrence of cancer at one anatomical site or of one morphological type) adds plausibility to a causal relationship, particularly when excess cancer occurrence is limited to one morphological type within the same organ. 

As mentioned previously, the causal connection between sleep difficulties and anxiety disorders are often impossible to determine in the clinical domain. The evaluation and treatment of sleep-specific pathologies may be as important as the evaluation and treatment of the anxiety disorders in these cases. Since hyperarousal is a common factor associated with both anxiety and sleep disturbances, the treatments for sleep problems are often similar to those targeting the reduction of worry, tension, and other manifestations of anxiety [73,74], However, treatments have also been developed to target specific aspects of certain anxiety disorders or sleep pathologies. 

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