Correspondence
The salience of the
motor domain in the
risk of psychosis
The study by Birgitte Klee Burton
and colleagues, 1 which capitalises
on the follow-up of a large cohort
of offspring of individuals with
a diagnosis of schizophrenia or
a diagnosis of bipolar disorder, marks
a step forward in the characterisation
of early endophenotypic expressivity
of the putative genetic predisposition
for schizophrenia (ie, schizotaxic
risk). The study confirms that in
those children, early childhood
motor impairment persists into preadolescence (from age 8 to 12 years)
and is also associated with the risk of
psychotic experiences.
This risk amplification pattern
points to the prognostic relevance
of early developmental phenotypes
and strengthens the rationale for
incorporating them in predictive
models for psychosis. Early neuro­
developmental deviations in the
motor domain have been repeatedly
indicated as suggesting a higher
risk of psychotic experiences, from
subthreshold trait-like schizotypal
personality features to full-blown
schizophrenia. 2 Nonetheless, it
remains underexplored, both
theoretically and clinically, why the
motor domain is apparently more
salient and intimately associated
with psychotic risk than other
neurocognitive domains. In other
words, do childhood motor problems
represent something more than
just one of many neurocognitive
epiphenomena of an altered
neurodevelopment?
We argue that it is possible that
a neurophysiological mechanism
that is altered in childhood motor
impairment, corollary discharges, also
plays a role in later developmental
trajectories that lead to the onset
of psychotic symptoms. 3 Corollary
discharges are copies of motor
commands used to form a prediction
314
of the sensation from self-generated
movements. On a phenomenological
level, early alterations of corollary
discharges are likely to interfere
with the development of the basic
sense of self, with a related effect on
embodiment (ie, less pre-reflective
attunement with one’s body) and
reduced feelings of agency (ie, the
subjective, implicit experience of
intentionally controlling one’s acts).
Indeed, so-called positive psychotic
symptoms, such as passivity delusions
and auditory hallucinations, typically
arise when an attenuation of the
sense of ownership of and agency
over one’s mental states reaches the
extreme that self-generated actions
are misattributed to an external
source. Therefore, early impairments
of corollary discharge, expressed
by childhood motor impairment,
might result in initial distortions of
subjective experience, which might
in turn facilitate the emergence of
the subclinical modes of experience
that precede the onset of positive
symptoms—ie, self-disorders. These
subclinical experiences are trait-like,
non-psychotic anomalies of subjective
experience and have been suggested
to be schizophrenia spectrum
vulnerability phenotypes. They typically
encompass a cluster of experiential
distortions, akin to depersonalisation
and derealisation, characterised by
a diminished sense of existing as
an embodied, coherent, and active
subject, vitally immersed in the world.4,5
More longitudinal research is needed
to support the proposed mechanism
between motor impairment and the
genesis of psychosis.
We declare no competing interests.
*Michele Poletti, Andrea Raballo
michele.poletti@ausl.re.it
Child and Adolescent Neuropsychiatry Unit,
Department of Mental Health and Pathological
Addiction, Azienda USL-IRCCS di Reggio Emilia,
42122 Reggio Emilia, Italy (MP); Faculty of
Biomedical Sciences, Università della Svizzera Italiana,
Lugano, Switzerland (AR); Cantonal Socio-psychiatric
Organization, Public Health Division, Department of
Health and Social Care, Repubblica e Cantone Ticino,
Mendrisio, Switzerland (AR)
1
2
3
4
5
Burton BK, Krantz MF, Skovgaard LT, et al.
Impaired motor development in children with
familial high risk of schizophrenia or bipolar
disorder and the association with psychotic
experiences: a 4-year Danish observational
follow-up study. Lancet Psychiatry 2023;
10: 108–18.
Burton BK, Hjorthøj C, Jepsen JR, et al. Research
review: do motor deficits during development
represent an endophenotype for
schizophrenia? A meta-analysis.
J Child Psychol Psychiatry 2016; 57: 446–56.
Poletti M, Gebhardt E, Kvande MN, et al. Motor
impairment and developmental psychotic risk:
connecting the dots and narrowing the
pathophysiological gap. Schizophr Bull 2019;
45: 503–08.
Raballo A, Poletti M, Preti A, Parnas J. The self
in the spectrum: a meta-analysis of the
evidence linking basic self-disorders and
schizophrenia. Schizophr Bull 2021;
47: 1007–17.
Henriksen MG, Raballo A, Nordgaard J.
Self-disorders and psychopathology:
a systematic review. Lancet Psychiatry 2021;
8: 1001–12.
We read with great interest the
Article by Birgitte Klee Burton and
colleagues in The Lancet Psychiatry
assessing motor development
and its association with psychotic
experiences in children with familial
high risk of schizophrenia or bipolar
disorder compared with controls. 1
This was one of the largest followup studies assessing motor function
deficit and other domains in
children with familial high risk of
schizophrenia or bipolar disorder to
date. We commend the authors for
the study, but we would like to discuss
several aspects of the study design
that could have influenced the study
findings.
First, the group of children at
familial high risk of schizophrenia
was matched with children who had
no biological parent diagnosed with
a schizophrenia spectrum disorder
or bipolar disorder. Although the
matching considered demographic
status, it did not consider socio­
economic status in view of its
intrinsic association with high-risk
status and to avoid overcorrection.
However, it has been observed that
individual as well community-level
socioeconomic status at the time of
birth is associated with an increased
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