diagnostic framing
12/12/2010
INTELLECTUAL DISABILITY, AUTISM AND SCHIZOPHRENIA: NEUROCOGNITIVE DEVELOPMENTAL DISORDERS
Intellectual Disability (ID), called ‘Mental Retardation’ in international diagnostic systems, represents a group of syndromes that shares a common extensive impairment of the development of neurocognitive functions. For this reason, the working group of the World Health Organization on the production of the chapter on intellectual disability in the eleventh edition of the International Classification of Diseases (ICD-11) system has proposed to replace the term ‘Mental Retardation’ with 'Intellectual Developmental Disorders’ (IDD).
The IDD would become part of neurodevelopmental disorders, the same theoretic diagnostic area in which Autism and Autism Spectrum Disorders (ASD) have been in for many years.
The hypothesis on alterations in brain development is now a core element of the majority of theories on the onset of schizophrenia, as well.
From the fetal period, in which the supposed vulnerability originates, until the onset of disease during adolescence, the brain would develop in order to make difficult or to impair the functioning of some knowledge systems of the outside world (cognitive functions).
Over the past three decades, thanks to many discoveries in molecular genetics and new techniques for recording images of the brain in action, the conceptualization of physiological and pathological neurodevelopment has grown. The formation of the central nervous system no longer refers solely to childhood but has come to include adolescence and adulthood, as well. Genes are no longer considered capable of directly encoding body structures. In fact, it has been found that they can be activated or deactivateddepending on what happens outside of the nuclei of neurons, of the brain, and of the whole person. In some cases, even when the DNA sequence does not have changes such as mutations, duplications or deletions, the transcription of RNA is still modified. A specific shape of the transcription is necessary for the construction of proteins which contributes to brain formation.
In neurodevelopmental disorders, the activity-dependent changes of gene expression and protein synthesis seem to integrate with the formation and with the gathering of interneuronal synapses in the formation of memory circuits and other basic cognitive functions.
Marco O. Bertelli
