Neurodevelopmental Disorders between Past and Future.

Dear Sir,

Neurodevelopmental disorders, according to the Diagnostic and Statistical Manual of Mental Disorders 5th edition (DSM-5), are characterized by early-onset deficits of variable severity in personal, social, academic, or occupational functioning. These disorders include, among others, intellectual disability, autism spectrum disorder, attention-deficit/hyperactivity disorder (ADHD), and communication disorders.[1] These same disorders had already been included in the DSM-IV, where they were placed one next to the other basically only based on a chronological criterion related to onset age, being included in the section titled “Disorders Usually First Diagnosed in Infancy, Childhood, or Adolescence.”[2] In this sense, DSM-5 produced an important step forward as it has highlighted the link between these disorders (see the preface of the respective chapter).[1] It is by no accident that clinical experience with cases affected by neurodevelopmental disorders suggests the presence of intermediate clinical pictures, such as those of patients with a severe speech disorder who present also with some behavioral atypias, but without qualifying as an autism spectrum disorder. Even the very frequent comorbidity between these disorders emphasizes the link between them. For example, in a percentage ranging from 26% to 68% of patients with autism spectrum disorder, there is an associated intellectual disability[3] while in 33%–37% of them, there is an associated ADHD;[4] not to mention the almost constant impairment of verbal language that in some cases may even be absent.[5]

The classification of neurodevelopmental disorders is quite complex, and at present, it should be considered as “in progress,” subject to significant changes, because it should meet different, sometimes diverging needs. On the one hand, there is the need for a diagnosis that is sufficiently precise and properly characterizing the clinical picture of the single individual, first of all for prognostic and therapeutic purposes, secondly for research purposes. On the other hand, there is the usefulness of a unifying vision that can highlight the common aspects and the contact points of these disorders for speculative purposes, aiming at constructing new models for neurodevelopment interpretation, and inspiring new research hypotheses. Just as in the developing brain, the various cortical areas are closely related between them, it is equally true that the respective functions assigned to these areas are correlated with each other in the context of a huge neuronal network, in which the dysfunction of a single sector can negatively impact even on distant areas producing an involvement of the whole system. In this perspective, it cannot be ruled out that in the future neurodevelopmental disorders will be considered basically as a single large group that encompasses numerous subgroups characterized by a predominant impairment, respectively, of intellectual functions (intellectual disability), intersubjectivity (autism spectrum disorder), or language (communication disorders), etc., putting aside rigid distinctions which, in practice, till now have proved to be of little use in both clinical practice and research, as suggested by Bourgeron proposing the use of dimensional and quantitative data rather than diagnostic categories.[6] Therefore, the DSM-5 classification of neurodevelopmental disorders is a useful tool but in its current form should be further improved.

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