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Should psychiatry deal only with mental disorders without an identified medical aetiology?

Celso Arango; David Fraguas. Should psychiatry deal only with mental disorders without an identified medical aetiology? World psychiatry : official journal of the World Psychiatric Association (WPA). 15 – 1, pp. 22 – 25. (Italia): 02/2016. ISSN 1723-8617.

Is psychiatry at risk of “losing” part of the conditions it deals with, once their “organic” or genetic origin is identified? The recent removal of Rett syndrome from the DSM‐5 autism spectrum disorders category illustrates this issue.

Rett syndrome is a neurodevelopmental disorder characterized by autistic symptoms, cognitive and motor abnormalities and decreased brain growth during childhood1. Most cases of the syndrome are caused by a mutation in the MeCP2 gene, although not everyone who has an MeCP2 mutation develops the syndrome1. It was originally included in the DSM‐IV as a disorder with autistic features of unknown aetiology. Now that its genetic origin has been identified, the main rationale for removing it from the DSM‐5 has been that it is considered a distinct entity with a specific aetiology.

The history of medicine contains several other examples where the discovery of the specific aetiology of a mental disorder (or a clinical condition once thought to fall within the realm of mental illness) led to its removal from the framework of psychiatry. In the 19th century, after the psychiatric symptoms of general paresis were attributed to neurosyphilis, that became the first psychiatric disease with definite organicity. Once this finding was confirmed, general paresis was progressively forced out of the field of psychiatry. Further, in 1943, penicillin was proved to be highly effective against primary syphilis. At that juncture, psychiatry definitively “lost” the treatment of general paresis.

However, if knowing the “organic” or genetic cause of a disorder is a rationale for its exclusion from the DSM, the very future of our specialty is at risk, since in time, as more specific underpinnings of mental disorders are identified, we may “lose” several of the clinical conditions we deal with. Currently, 10‐20% of patients with autism spectrum disorders and 40‐60% of those with severe intellectual disability are found to have clinically significant copy number variations or deleterious de novo mutations2, 3, and these rates continue to increase3. Removing disorders with a known medical aetiology from psychiatry makes as little sense as suggesting that, because some gastric ulcers can be caused by bacteria, they no longer belong in the field of gastroenterology.

Most of us would agree with the principle that without brain there is no mind. Beyond this frame, the mind‐brain debate remains inextricable. In a broad sense, mind or “psyche” may be conceived as a subjective phenomenal‐experiential realm4. The specificity of the conditions classified as psychiatric disorders lies in the peculiarity of the elements that compose them, i.e. mental symptoms that cannot be simplistically reduced to brain dysfunctions. Mental symptoms are rooted in both the natural and social sciences, caused by a blending of biological, semantic and social components5. In point of fact, clinical specialties are not grounded simply in our understanding of human biology. Rather, they emerge in complex ways in response to a variety of conditions and situations. Some specialties involve special skills (cardiac surgery) or disorders of organs (nephrology) or systems (gastroenterology). Other specialties arise in response to a type of disorder (oncology) or to stages of the life cycle (geriatrics). Psychiatry is for diagnosing and treating mental disorders.

During the 19th and 20th centuries, a schism arose between neurology and psychiatry, and the two went their separate ways6. Generally, neurology focused on disorders with cognitive and behavioural abnormalities and identifiable brain lesions – e.g., stroke, multiple sclerosis and Parkinson’s disease – while psychiatry focused on disturbances of mood and thought without identifiable brain lesions – e.g., schizophrenia, depression, and anxiety disorders6. However, the frontiers between neurology and psychiatry have never been clear‐cut, with notable areas of overlap between them. In fact, the historical “appropriation” of certain disorders by neurology or psychiatry – e.g., autism, attention deficit hyperactivity disorder (ADHD), Tourette’s syndrome, and dementia – seems to some extent arbitrary and based on extra‐clinical criteria6. Now, over a century later, the boundaries between neurology and psychiatry are being seriously questioned, and many voices within psychiatry are clamouring for it to become a clinical neuroscience7.

Yet, the fact that we will probably never be able to formulate a purely objective concept of most mental disorders does not make the search for possible “underlying” dysfunctions fruitless. On the contrary, the effort to find such dysfunctions is critical for the progress of the discipline. As an example, take two biological abnormalities that can be detected in some cases of schizophrenia: chromosome 22q11.2 deletion and presence of anti‐N‐methyl‐D‐aspartate receptor (NMDA‐R) antibodies.

Chromosome 22q11.2 deletion syndrome is usually defined as a genomic disorder with markedly variable expressivity, associated with high rates of psychotic disorders (including schizophrenia), mood disorders, anxiety disorders or ADHD. Remarkably, there is not a differential symptomatic expression in subjects with 22q11.2 deletion‐related schizophrenia as compared to other individuals with a diagnosis of schizophrenia8.

Antibodies against the NMDA‐R may be found in around 1‐2% of patients with a clinical diagnosis of schizophrenia9. Several patients with NMDA‐R serum antibodies develop a multistage symptomatology that progresses from psychosis, memory deficits, seizures, and language disintegration to a state of unresponsiveness with catatonic features. However, some patients with NMDA‐R antibodies fully meet the criteria for schizophrenia9. These antibodies may represent an aetiological factor of schizophrenia, potentially treatable with a specific therapy.

The fact that schizophrenia can be linked to specific aetiological factors such as chromosome 22q11.2 deletion, anti‐NMDA‐R antibodies, more than a hundred genetic loci, or greater proportions of rare copy number variations (i.e., recurrent 16p11.2 duplications, 3q29 deletions, or 17q12 duplications)10 is no reason for this condition to be removed from the field of psychiatry.

Psychiatrists should be able to deal with mental disorders independent of their aetiology. Finding a specific biological aetiology should be a joyous occasion to vindicate the key role of psychiatry as the medical specialty that deals with mental disorders, regardless of whether their aetiology is known or unknown.

1. McGraw CM, Samaco RC, Zoghbi HY. Science 2011;333:186. [PubMed]
2. Gilissen C, Hehir‐Kwa JY, Thung DT et al. Nature 2014;511:344‐7. [PubMed]
3. Sebat J, Lakshmi B, Malhotra D et al. Science 2007;316:445‐9. [PubMed]
4. Parnas J, Sass LA, Zahavi D. Schizophr Bull 2013;39:270‐7. [PubMed]
5. de Leon J. Rev Psiquiatr Salud Ment 2014;7:186‐94. [PubMed]
6. Martin JB. Am J Psychiatry 2002;159:695‐704. [PubMed]
7. Insel TR, Cuthbert BN. Science 2015;348:499‐500. [PubMed]
8. Owen MJ, Doherty JL. World Psychiatry 2016;15:23‐5. [PubMed]
9. Pollak TA, McCormack R, Peakman M et al. Psychol Med 2014;44:2475‐87. [PubMed]
10. Schizophrenia Working Group of the Psychiatric Genomics Consortium . Nature 2014;511:421‐7.[PubMed]
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