Plasma Beta-Endorphin Concentrations in People with Learning Disability and Self-Injurious and/or Autistic Behaviour

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Abstract
Background It has been suggested that the key variable in reduced plasma immunoreactive β-endorphin concentrations in autistic subjects may be concomitant self-injurious behaviour. Method We studied morning levels of plasma β-endorphin in 33 learning disabled people with self-injurious and/or autistic behaviour. Results The β-endorphin level of the subjects with severe self-injurious behaviour proved to be significantly lower than that of autistic subjects without severe self-injurious behaviour (3.6 (1.4) pmol/l v. 5.8 (4.3) pmol/l; t-test: P = 0.045. Replication: 3.7 (1.1) pmol/l v. 5.7 (3.8) pmol/l; t-test P = 0.043). Individuals with mild and occasional self-injurious behaviour were found to have β-endorphin levels comparable to those without self-injurious behaviour. Further, subjects being treated with neuroleptics had lower β-endorphin levels than untreated subjects. Conclusions These results stress that in any study of opioid systems of learning disabled people, it is very important to differentiate between people with and without severe self-injurious behaviour. The results support the idea that severe self-injurious behaviour may be related to functional disturbances in the endogenous opioid system.