Recognizing Psychiatric Comorbidity With Reading Disorders

Abstract

Reading disorder (RD), a specific learning disorder (SLD) of reading that includes impairment in word reading, reading fluency, and/or reading comprehension, is common in the general population but often is not comprehensively understood or assessed in mental health settings. In education settings, comorbid mental and associated disorders may be inadequately integrated into intervention plans. Assessment and intervention for RD may be delayed or absent in children with frequently co-occurring mental disorders not fully responding to treatment in both school and mental health settings. To address this oversight, this review summarizes current knowledge regarding RDs and common comorbid or co-occurring disorders that are important for mental health and school settings. We chose to highlight RD because it is the most common SLD, and connections to other often comorbid disorders have been more thoroughly described in the literature. Much of the literature we describe is on decoding-based RD (or developmental dyslexia) as it is the most common form of RD. In addition to risk for academic struggle and social, emotional, and behavioral problems, those with RD often show early evidence of combined or intertwined Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition childhood disorders. These include attention deficit hyperactivity disorder, anxiety and depression, disruptive, impulse-control, and conduct disorders, autism spectrum disorders, and other SLDs. The present review highlights issues and areas of controversy within these comorbidities, as well as directions for future research. An interdisciplinary, integrated approach between mental health professionals and educators can lead to comprehensive and targeted treatments encompassing both academic and mental health interventions. Such targeted treatments may contribute to improved educational and health-related outcomes in vulnerable youth. While there is a growing research literature on this association, more studies are needed of when to intervene and of the early and long-term benefits of comprehensive intervention.

Full text

March 2018 | Volume 9 | Article 1011
REVIEW
published: 27 March 2018
doi: 10.3389/fpsyt.2018.00101
Frontiers in Psychiatry | www.frontiersin.org
Edited by:
Marin Veldic,
Mayo Clinic, United States
Reviewed by:
Didem Oztop,
Erciyes University, Turkey
Katerina Maniadaki,
Technological Educational Institute of
Athens, Greece
Pratibha N. Reebye,
British Columbia Children’s Hospital,
Canada
*Correspondence:
Robert L. Hendren
robert.hendren@ucsf.edu
Specialty section:
This article was submitted to Child
and Adolescent Psychiatry,
a section of the journal
Frontiers in Psychiatry
Received: 18October2017
Accepted: 13March2018
Published: 27March2018
Citation:
HendrenRL, HaftSL, BlackJM,
WhiteNC and HoeftF (2018)
Recognizing Psychiatric Comorbidity
With Reading Disorders.
Front. Psychiatry 9:101.
doi: 10.3389/fpsyt.2018.00101
Recognizing Psychiatric
Comorbidity With Reading Disorders
Robert L. Hendren1,2*, Stephanie L. Haft1, Jessica M. Black3, Nancy Cushen White2,4 and
Fumiko Hoeft1,2,5,6,7
1 Division of Child and Adolescent Psychiatry, Department of Psychiatry, Weill Institute for Neurosciences, University of
California San Francisco, San Francisco, CA, United States, 2 Dyslexia Center, University of California San Francisco,
SanFrancisco, CA, United States, 3 School of Social Work, Boston College, Chestnut Hill, MA, United States,
4 Departmentof Pediatrics, University of California San Francisco, San Francisco, CA, United States, 5 University of California
Multi-Campus Precision Learning Center (PrecL), San Francisco, CA, United States, 6 Haskins Laboratories, New Haven, CT,
United States, 7 Department of Neuropsychiatry, Keio University School of Medicine, Tokyo, Japan
Reading disorder (RD), a specic learning disorder (SLD) of reading that includes impair-
ment in word reading, reading uency, and/or reading comprehension, is common in the
general population but often is not comprehensively understood or assessed in mental
health settings. In education settings, comorbid mental and associated disorders may
be inadequately integrated into intervention plans. Assessment and intervention for RD
may be delayed or absent in children with frequently co-occurring mental disorders not
fully responding to treatment in both school and mental health settings. To address
this oversight, this review summarizes current knowledge regarding RDs and common
comorbid or co-occurring disorders that are important for mental health and school set-
tings. We chose to highlight RD because it is the most common SLD, and connections
to other often comorbid disorders have been more thoroughly described in the literature.
Much of the literature we describe is on decoding-based RD (or developmental dyslexia)
as it is the most common form of RD. In addition to risk for academic struggle and
social, emotional, and behavioral problems, those with RD often show early evidence
of combined or intertwined Diagnostic and Statistical Manual of Mental Disorders, Fifth
Edition childhood disorders. These include attention decit hyperactivity disorder, anxiety
and depression, disruptive, impulse-control, and conduct disorders, autism spectrum
disorders, and other SLDs. The present review highlights issues and areas of controversy
within these comorbidities, as well as directions for future research. An interdisciplinary,
integrated approach between mental health professionals and educators can lead to
comprehensive and targeted treatments encompassing both academic and mental
health interventions. Such targeted treatments may contribute to improved educational
and health-related outcomes in vulnerable youth. While there is a growing research
literature on this association, more studies are needed of when to intervene and of the
early and long-term benets of comprehensive intervention.
Keywords: specic learning disorder, developmental dyslexia, comorbidity, mental health, neurodevelopmental
INTRODUCTION
Despite a strong reciprocal association between reading disorder (RD) and mental disorders in
young people (1), their co-occurrence is oen under-recognized and under-treated resulting in less
than optimal outcomes in all areas including emotional outcomes. Diculties with comorbidities
may continue into adulthood (2). Recognition of RD by health-care professionals is important—the

FIGURE 1 | Current issues, areas of investigation, and suggestions for future research in conditions commonly occurring with RD in children. RD, reading disorder;
ADHD, attention decit hyperactivity disorder; ASD, autism spectrum disorder; SLD, specic learning disorder; CD, conduct disorder; ODD, oppositional deant
disorder.
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prevalence of dyslexia (decoding-based RD; the term RD is used
from hereon) is approximately 5–10% of all children depending
on the study across languages, cultures, and writing systems (3).
In an eort to bridge the recognition gap between RD and
associated mental disorders, we review RD along with other co-
occurring Diagnostic and Statistical Manual of Mental Disorders,
Fih Edition (DSM-5) mental disorders. We also review literature
that describes best practice interventions for children with RD and
comorbid disorders and identify areas where stronger research
is important (Figure1). Our overarching goal is to increase the
awareness of health professionals to disorders of reading that
overlap or are confused with mental conditions and disorders.
DSM-5 denes RD, within neurodevelopmental disorders, as
a type of specic learning disorder (SLD) with impairment in
reading that is characterized by problems with word reading
accuracy, reading uency, and reading comprehension that are
not the result of sensory impairments, neurological disorders,
intellectual disabilities, or inadequate educational instruction
(4). e impairments in word reading accuracy or reading u-
ency are also noted as developmental dyslexia in the literature.
RD is oen associated with diculties in phonological aware-
ness (awareness of sounds of a language, i.e., phonemes, to
process spoken and written language), lexical uency (i.e., rapid
naming of common items), letter (sound) knowledge, graph-
eme–phoneme association, which are predictive of later decod-
ing and word reading. Oral language, vocabulary, and executive
function on the other hand are generally more predictive of
reading comprehension. Diculties in reading comprehension
may be a result of reduced reading experience that can impede
growth of vocabulary and background knowledge in those with
decoding-based RD (5). However, it is possible for children with
specic reading comprehension decits to have intact decoding
skills (6).
METHODS
We used two electronic databases (PubMed and PsycInfo) in
order to review prevalence and characteristics of RD’s comorbid-
ity with other psychiatric disorders. Searching for relevant articles
from the past 20years (1997–2017), we used the keywords such
as “dyslexia,” “reading disability,” “reading disorder,” “learning
disability,” “learning disorder” along with “comorbid,” and/or
terms pertaining to other specic DSM-5 disorders [e.g., “autism
and Autism Spectrum Disorder (ASD),” “Attention Decit

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Hyperactivity Disorder (ADHD),” “anxiety,” “depression,” “con-
duct disorder,” etc.]. We primarily selected articles with a focus
on child populations (individuals under the age of 18years) and
a specied diagnosis of RD.
Overview of RD
Etiology
Reading disorder results from a constellation of genetic and
environmental risk factors and their interactions and not a
single underlying cause. e estimated heritability rate of RD is
approximately 50–70% (7, 8). Several susceptibility genes have
been identied (8), though each explains only a small fraction
of variance, suggesting the involvement of other mechanisms
including polygenicity, epistasis, and epigenetics, in RD (9).
Neuroanatomical anomalies in both gray and white matters
shown to be causally related to RD (10) are observed in areas
and networks associated with phonological, orthographic, and
articulatory processing (11–13). Additionally, work in neural
oscillations as well as neurochemistry shows decits related to
sensory processing, particularly auditory discrimination, in
individuals with or at-risk for RD (14, 15). Within the context
of comorbidity, the pathophysiology oen overlaps between RD
and co-occurring mental disorders. For example, RD shares com-
mon risk genes with ADHD (16, 17). In ASD, links to language
impairment (LI) such as specic language impairment (SLI) have
been made (18), which in turn may be associated with RD risk
genes (19). Neuroimaging studies of RD comorbidity with mental
disorders are currently limited but hold promise for elucidating
shared versus dierential etiologies. For instance, one neuroim-
aging study found distinct neural biomarkers for children with
dyslexia, ADHD, and age-matched controls in auditory neuro-
anatomy, physiology, and behavior (20).
Early Characteristics
In those at-risk for developing decoding-based RD, decits in
pre-literacy skills (e.g., phonological awareness, letter identica-
tion and letter-sound knowledge, and rapid naming) are observed
(21). A growing body of research also implicates non-linguistic,
domain-general abilities in early literacy acquisition and RD, such
as visual attention (22) and executive functions (23). Decoding-
based RD is oen noticed initially in kindergarten or rst grade
when children are rst exposed to formal reading instruction and
may be diagnosed between 2nd and 4th grade, depending on the
educational system, parents, caregivers, and teachers. RD of read-
ing comprehension tends to be identied later as the demands
of reading increases from learning to read to reading to learn,
unless children are initially diagnosed in earlier years with SLI.
ough proles of specic comorbidities will be discussed in later
sections, the general pattern is that RD in combination with a
comorbid condition results in greater impairment.
Assessment and Diagnosis
In order to obtain a formal diagnosis of RD, a child must undergo
a battery of tests that are administered by a qualied professional
(diagnostician qualications vary by state). Careful considera-
tion of the potential for co-occurring disorders or impairments
and other interacting factors is critical for ensuring accurate
diagnoses to inform recommendations for intervention or treat-
ment—and for predicting prognosis. For example, it would be
important to determine whether a child presents with ADHD and
has a secondary diculty in reading or presents with RD that
results in inattention.
Prior to assessment, it is important to obtain the child’s fam-
ily, developmental, and educational history. Sensory issues (e.g.,
impairment in vision or hearing), home and school literacy
environment, native language (e.g., English learners who lack
English prociency) that may aect reading should be ruled out
as causes of diculty; at the same time, it must be kept in mind
that the presence of these issues do not necessarily preclude exist-
ence of RD. Parental self-report scales of reading and attention
diculties may be useful for identication of adults at-risk for
these diculties, since at-risk parents may confer risks on their
children for related problems (24).
COMORBID MENTAL DISORDERS
Neurodevelopmental Disorders
Attention Decit Hyperactivity Disorder
Attention decit hyperactivity disorder and RD are recognized
as frequently comorbid disorders (Ta bl e 1 ). ADHD involves an
unremitting pattern of inattention and/or hyperactivity–impul-
sivity that results in functional impairment (4). RD oen involves
attention diculties, sometimes representing overlooked and
undertreated ADHD (25), which can contribute to academic
underachievement (26). Subgroups of children with RD show
attention-related impairments (e.g., decits in alertness, covert
shi of attention, divided attention, exibility, and visual search)
(27). In experimental work, researchers have shown attention-
related decits in RD in both the auditory (attention shiing)
(28) and visual domains (which some argue is an independent
contributor to phonological decits) (29).
Approximately 20–40% of children with the inattentive sub-
type of ADHD have RD (50, 51) and 20–40% of those with RD
have ADHD (33). e relationship between ADHD symptoms
and reading is found to be predominantly in the inattentive type
(30, 31). Neuropsychological proles of RD and ADHD comor-
bid groups include decits in processing speed, verbal working
memory, phonological short-term memory, naming speed, and
central executive processes (32, 33). A strong explanation for this
comorbidity proposes that multiple predictors of each disorder
have shared or overlapping genetic (16, 17), as well as neural and
cognitive risk factors. A proposed subgroup of ADHD, “sluggish
cognitive tempo,” characterized by diculty sustaining attention,
daydreaming, lethargy, and physical underactivity, is thought by
some to represent a possible link to RD (52) using electrophysi-
ological (53) and pharmacological (54) evidence. Imaging stud-
ies, however, have generally found distinct patterns of structural
and functional abnormalities among RD and ADHD, most oen
examined separately (55).
e research on comorbidity between RD and ADHD is
extensive—for reviews, see Ref. (17, 33, 56). However, the com-
bined developmental progression of RD + ADHD is not well
studied. Further research is needed of the overlap or intertwined

TABLE 1 | An overview of comorbid conditions that commonly occur with reading disorder (RD) as well as their shared symptoms and risk mechanisms.
Comorbid condition Features of comorbid group Shared risk with RD
Attention decit hyperactivity disorder (ADHD) Inattention (30, 31) in auditory (28) and visual (29)
Decits in processing speed, verbal working
memory, phonological short-term memory, naming
speed, and central executive processes (32, 33)
Shared risk genes (KIAA0319 and DCDC2) (17)
Shared structural and functional neural abnormalities (33)
Environmental factors (smoke and miscarriage) (16)
Autism spectrum disorder Impaired reading comprehension (34) Shared risk genes (MRPL19) (19)
Comorbidity with language impairment (35)
Disruptive, impulse-control, and conduct
disorders
Externalizing behavior (36, 37) Shared cognitive risk in working memory decit (38)
Comorbidity with ADHD (39–41)
Decits in verbal processing/language skills (38, 42)
Anxiety and depressive disorders Poor self-esteem (43)
Internalizing psychopathology (44)
Negative academic/social experiences (45)
Shared familial risk factors (46)
Other specic learning disorders Internalizing psychopathology (47)
Handwriting decits (48)
Shared cognitive risk in working memory, semantic memory, and
verbal processing decits (49)
Decits in rhythmic organization (48)
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nature of the two disorders and the inuence of this potential
co-contribution during the development of reading.
Autism Spectrum Disorder
ere are limited studies of ASD+RD children, and the preva-
lence of RD reported in ASD children ranges considerably from
6 (57) to 30% (58). One consideration in discussing co-occurring
ASD and RD is dierentiating between “true” comorbidity and
symptom overlap—a recurring issue in child psychopathology. In
both ASD and RD, there are documented impairments in read-
ing comprehension, language, and visual/auditory processing.
However, simply counting these overlaps in cognitive symptoms
in ASD and RD may lead to false recognition of comorbidity. On
the other hand, failure to recognize a comorbid RD could result
in inadequate treatment with negative academic consequences.
Reading disorder and ASD might not be considered “true” co-
occurring disorders because the reading diculty in ASD is not
a decoding or phonics problem. Numerous studies report reading
comprehension decits in children with ASD that are discrepantly
low with their intelligence [see Ref. (59) for meta-analysis], which
typically do not fall under decoding-based RD. In fact, though
reading comprehension impairment in ASD children is well-
documented (34), ASD children oen show intact and sometimes
even precocious abilities in word reading, non-word decoding,
and text reading accuracy (60). ese ndings suggest that the
reading decits observed in ASD are dierent than that of a child
with decoding-based RD, which are characterized by phonologi-
cal decits that may lead to impaired reading comprehension.
One way to further explore if ADHD+RD represent a “true”
comorbidity is to examine the possibility of shared etiological fac-
tors. One explanation for shared reading problems is co-occurring
LI. LI is prevalent in both ASD (61) and RD (62), and studies
suggest that the presence of reading comprehension decits in
children with ASD is mediated by language ability (35, 61). ese
behavioral results are supported by a study showing that genes
contributing to general language skills are shared among dyslexia,
ASD, and LI (19). However, LI is certainly not the sole contributor
to reading problems in ASD—some literature shows a correlation
between social abilities and reading comprehension in ASD
(60). In other words, the behavioral manifestation of reading
impairment in ASD and RD originates at least partly from dif-
ferent mechanisms; however, longitudinal and family studies are
needed to further explore how the disorders may be related. As
discussed in the treatment section, the underlying explanation for
the RD and ASD comorbidity has important implications for how
comorbid RD is treated in children with ASD, and further study is
needed to determine the most eective dierential interventions.
Other SLDs
Historically, the subtypes of SLDs have been viewed from an
academic-subject approach—for example, the DSM-4 had
distinct categories for RD, mathematics disorder (MD or dyscal-
culia), disorder of written expression (dysgraphia), and learning
disorder not otherwise specied. e DSM-5 moved away from
these categories in including RD, MD, and dysgraphia together
under the label of “Specic Learning Disorder” with speciers
for the area of impairment. ese areas of impairment can be
further broken down into component subskills in the areas of
reading (e.g., word reading accuracy, reading uency, and reading
comprehension), mathematics (e.g., number sense, calculation,
and math reasoning), and writing (e.g., spelling, grammar, and
written expression). In a move from a categorical to a dimensional
approach, research has sought to identify comorbidities among
the SLDs through the lens of shared versus unique cognitive
processes that might underlie them.
Reading disorder and MD have a comorbidity of approxi-
mately 40% (63), and this co-occurrence is associated with greater
impairment on measures of internalizing psychopathology and
academic functioning (47). Although RD and MD are generally
accepted to have unique neurocognitive proles, researchers
have pointed to shared cognitive processes in working memory,
semantic memory, and verbal processes that may explain the high
comorbidity (49). One recent paper applied a cluster analysis to
children with SLD to identify associations between cognitive clus-
ters and SLD subtypes. Results showed that impaired subskills of
each domain were associated with dierent clusters—for example,

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math and text reading speed were most strongly associated with a
cluster involving cognitive processing, while text comprehension
was more linked to the verbal abilities cluster (64). is approach
is promising in recognizing the heterogeneity within RD and
MD themselves, as well as adopting a dimensional approach to
highlight shared cognitive decits.
Reading disorder has also been shown to co-occur with
dysgraphia. Comorbidity rates between RD and dysgraphia are
dicult to determine, yet the correlation of word reading and
writing performance is shown to be around 70% (65). Although
RD and dysgraphia are shown to have dierences in brain bases
for written language tasks (66), they exhibit shared behavioral
decits in rhythm, which is required for both reading and writing
(48). Most researchers have explained the overlap of dysgraphia
and dyslexia by highlighting learning to read and learning to spell
as “two sides of the same coin” (65). Phonological awareness,
visual attention, working memory, and auditory processing play
predictive roles in both reading and writing (67).
Further research is warranted on examining comorbidities
between RD and other SLDs from a process perspective. In par-
ticular, studies should examine trajectories of impairment in these
cognitive processes from before the onset of formal schooling to
adult years when “compensation” for decits may have occurred.
Disruptive, Impulse-Control, and Conduct
Disorders (CDs)
Children with RD can exhibit comorbidities in the disruptive,
impulse-control, and CD categories of the DSM-5 including CD
and oppositional deant disorder (ODD) (4). Most of the exist-
ing literature focuses on associations between RD and behavioral
problems or disorders in general, though specic links between
RD and diagnosed CD (68) have been established. It is not clear,
however, how much of the higher incidences of externalizing
behavior among children with RD precedes RD or is the emotional
result of it (36, 37). Although more recent studies have found that
reading diculties oen precede behavioral problems, results do
not necessarily support a direct causal pattern between the two
conditions. Instead, conduct and behavioral issues in RD children
are exhibited across both academic and non-academic settings
and appear more independent of reading problems (69, 70).
ese ndings are important in implying that interventions for
RD may not treat co-occurring behavioral problems—however,
such treatment studies have yet to be conducted and represent an
area of needed research.
One promising explanation for the co-occurrence of RD
and behavioral disorders is each conditions’ comorbidity with
ADHD—ADHD commonly occurs with RD, CD, and ODD
(71), and ADHD and RD are associated with higher delinquency
severity scores than for either one alone (72). Further support for
this explanation comes from studies showing that hyperactivity
mediates between reading problems and disruptive behaviors
in adolescent populations (39, 73). However, one study of adult
forensic patients with RD found a higher level of cognitive impul-
sivity than those without RD, regardless of ADHD diagnosis (74).
An additional explanation for the comorbidity of these condi-
tions with RD involves shared neurocognitive risk factors—for
example, children diagnosed with disruptive and CDs are shown
to have abnormal language processing (42) and working memory
decits (38), characteristics also shared by children with RD. Taken
together, these results suggest that the comorbidity of disruptive,
impulse-control, and CDs and RD are at least partially due to each
disorders’ co-occurrence with ADHD. Further study is needed
to determine how the co-occurrence of RD and CD/ODD may
dier with or without the presence of comorbid ADHD. is will
inform the most eective timing and nature of interventions to
improve outcomes for RD and intertwined behavioral disorders.
Anxiety Disorders
Children with RD report greater generalized anxiety than their
non-RD peers (44), and a meta-analysis has conrmed that LD
children and adolescents, including those with RD, have signi-
cantly higher scores on anxiety measures than non-LD students
(75). is higher rate of anxiety in RD children persists even
aer controlling for ADHD symptoms (76). In explaining this
comorbidity, researchers have proposed a model whereby anxiety
distracts from learning and interferes with cognitive processes
necessary for reading, leading to potential RD (77). However,
researchers have also proposed that reading problems associated
with RD can lead to anxiety as a result of the experience of school
failure (78). More neurodevelopmental longitudinal studies are
needed to investigate these processes, although current evidence
suggests that both models have merit, with a bi-directional rela-
tionship between anxiety and reading (79).
In order to investigate a potential genetic etiology for the
RD-anxiety comorbidity, researchers have studied siblings and
twin pairs. One study of monozygotic and dizygotic adult twins
found a strong link between anxiety and RD but with no shared
genetic cause (45). A separate study demonstrated that siblings of
children and adolescents with RD were more than twice as likely
to meet criteria for generalized anxiety disorder (GAD), suggest-
ing shared familial risk factors between the two disorders (46).
e study also showed marginally signicant dierences between
monozygotic and dizygotic twin pairs in RD cross-concordance
with GAD, indicating a small role for genetic risk in the comor-
bidity between RD and anxiety. Although more work is needed
on neural correlates of comorbidity, these genetic studies support
the model of a combination of genetic and environmental risk
factors in explaining co-occurrence of RD and anxiety.
One area of future research involves distinguishing between
comorbidity of RD and general anxiety versus anxiety specic
to reading (reading anxiety). Reading anxiety as a concept has
not been investigated in the literature, but over three decades of
research on math anxiety indicate that its neural and behavioral
characteristics are related but distinct from general anxiety [see
Ref. (80, 81) for reviews on math anxiety]. ere is no doubt that
RD is commonly comorbid with general anxiety, but investigating
the potential presence of reading anxiety could enable more tar-
geted interventions to address co-occurring emotional problems
children with RD. Unfortunately, there are currently no measures
to assess reading anxiety, representing an area of need in the eld.
Depressive Disorders
In addition to or potentially as a result of anxiety, children and
adolescents with RD exhibit higher rates of depression (44, 82),

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with evidence for a correlation between more severe RD and
greater depressive symptoms in younger children (83). Similar
to the research on RD and anxiety association, the existence of
depression in RD does not appear to be dependent on comorbid-
ity with ADHD (84). Researchers have identied low self-esteem
as a symptom of depression in RD as well as a target for interven-
tion (85, 86)—in one study of adolescents with RD, self-esteem
predicted 23% of the variation in depression risk (87). Depression
and RD exhibit patterns of familial risk and marginally signicant
genetic contributions similar to that of RD and anxiety (46), sug-
gesting multiple risk factors. e higher incidence of bullying and
peer victimization faced by children and adolescents with RD
may be an environmental factor that partially explains comorbid-
ity with depression (88) but further study of neurodevelopmental
risk factors will likely provide targets for early interventions.
For example, a growing area of research suggests that emo-
tion processing may be impaired in children with RD (89).
is impairment has important implications for assessing for
comorbid depression and anxiety in RD (44), since decits in
understanding emotions, depressive and anxious symptoms may
go underreported. us, self-report measures may not be su-
cient to assess for comorbid depression and anxiety in RD youth.
Other Disorders and Conditions
Reading disorder can sometimes co-occur with other DSM-5
categories, though these appear to be less investigated than the
aforementioned conditions. Although RD is not listed as a com-
mon comorbid condition in the category of sleep-wake disorders
and vice versa, a recent exploratory study found a signicantly
greater frequency of sleep disorders in RD children compared to
controls (90). Given that a prior neurophysiological study showed
an association between sleep activity and reading abilities in RD
children (91), evaluation of sleep may be an important factor to
consider in RD treatment and management.
Reading disorder may also co-occur with disorders more
commonly appearing in adulthood. For instance, one study of
substance-related and addictive disorders showed that out of a sam-
ple of adults with addiction issues, 40% had RD (92). However, a
separate study reported signicantly lower substance use history
in RD versus non-RD university students (93). Future research
is therefore needed to draw conclusion about the comorbidity
of RD and substance abuse. Similarly, due to the rarity of early
onset schizophrenia, RD and schizophrenia have not been shown
to co-occur in children, but one study found that 70% of adult
patients with schizophrenia met criteria for RD (94). However,
this nding may be confounded in part by reduced educational
and occupational outcomes (94), as well as IQ changes that may
occur with progression of schizophrenia (95). Finally, a form of
RD can occur in patients with the neurocognitive disorder of
dementia (96) and may share susceptibility genes (97), though
this is only observed in adult populations.
TREATMENT
A challenge in treating comorbid conditions is whether to target
both conditions simultaneously or to treat one condition to see
if benet in the other condition results. However, there is a gap
in the literature of evidence-based strategies for treating RD with
comorbid conditions, likely because investigations of treatments
oen intentionally exclude individuals with comorbidities. is
is further complicated by the fragmented approach to treatment
a child with RD may receive. For example, an educator may focus
on treating one symptom (e.g., decoding) while a psychiatrist
may target another (e.g., anxiety). e majority of studies of
interventions for comorbid RD are with ADHD with few to no
studies of other comorbid conditions such as ASD, CD, anxiety,
or depression.
Reading Interventions
Phonics-based reading instruction is the most common and
most eective intervention for students with RD (98) and for
poor readers (99). Phonics instruction that is systematic and
explicit has the greatest evidence (100). Instruction designed
to explicitly teach adult students to assign selective attention to
grapheme–phoneme associations—as opposed to attempts to
memorize whole unfamiliar words—impacts brain circuitry that
can subsequently be recruited during reading (101). Reading
interventions are eective for students with and without RD
when administered by teachers or researchers (102). Although
music education has also been investigated as a way to improve
reading in children with RD, evidence does not currently support
its eectiveness (103).
Reading interventions in comorbid ADHD+RD are shown
to be eective regardless of adjunctive ADHD medications (104).
In a recent paper, ADHD treatment alone resulted in greater
reduction in ADHD symptoms than reading treatment alone,
and reading treatment led to greater improvements in reading
outcome (word reading and decoding) than ADHD treatment
only. e administration of both treatments simultaneously did
not result in a greater level of improvement of each outcome
(ADHD symptoms and reading skills). In other words, there was
no additive value to combining treatments. However, the com-
bined treatment enabled remediation of both ADHD and reading
symptoms in the comorbid group simultaneously, so would still
be recommended over treating each disorder in isolation (105). It
should be noted that this study involved predominantly African
American males and should be replicated with a diverse range of
demographics.
To be most eective, children with RD and comorbid condi-
tions may need reading interventions to be more specic or
combined with other interventions. For example, children with
RD+MD who received both reading intervention and number
combination intervention outperformed RD+MD students who
received reading intervention alone (106). Reading intervention
may also need to specically target the unique reading proles of
subjects with comorbidities. Children with ASD and comorbid
reading problems show a prole of intact decoding abilities, yet
low reading comprehension, and accordingly, reading interven-
tion specically targeting vocabulary skills is shown to be most
eective in this population (107, 108).
Socioemotional Health
Because children with RD may be exposed to signicant
stressors, and RD can co-occur with anxiety and depression,

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Frontiers in Psychiatry | www.frontiersin.org March 2018 | Volume 9 | Article 101
treatments should address socioemotional health in addition
to reading. Protective factors that foster resilience for children
and adolescents with RD include self-advocacy tools, strength
identication, and social connections (109). However, research
on evidence-based treatments for depression and anxiety that
commonly occur with RD is inadequate and is a critically impor-
tant area for future work. Cognitive behavioral therapy (CBT),
a treatment that focuses on altering negative behavioral and
thought patterns, may reduce symptoms of comorbid anxiety
and depression in RD children. CBT is the standard for treat-
ing unidimensional cases of anxiety and depressive disorders
(110, 111) and is shown to be eective in treating psychiatric
comorbidities in other conditions that co-occur with RD, such
as ADHD (112) and ASD (113). More research is needed to
delineate unique modications that might be necessary for the
greatest eectiveness when the emotional condition is combined
with RD.
Mindfulness meditation shows increasing promise for benet
to socioemotional health in people with these combined dis-
orders. Mindfulness meditation is shown to reduce anxiety in
RD adolescents (114). It is also shown to improve attention and
lexical processing/word reading (but not non-word decoding)
in combined RD and ADHD in adults, more so than in those
with RD only (115). A mindfulness intervention incorporating
elements of CBT was shown to improve ODD and CD symp-
toms in RD+ ADHD adolescents, as well as reduce anxiety in
RD+anxiety adolescents. Academic performance is thought to
be improved through the reduction in anxiety as a result from
mindfulness meditation among youth with RD and comorbid
conditions (114).
Biomedical and Nutritional
Pharmacotherapy is increasingly investigated for combined RD
and comorbid conditions, although the most common treatment
for RD alone is reading interventions. e great majority of these
studies examined RD with comorbid ADHD. Results from these
studies are summarized in recent reviews (56, 116). In summary,
these studies have investigated the use of atomoxetine (ATX),
methylphenidate (MPH), and nutritional supplements such as
polyunsaturated fatty acids (117) on outcomes of reading, ADHD
symptoms, and executive functions in ADHD + RD groups.
Reviews reporting on treatment studies found that outcome
eect sizes range from small to medium [as low as 0.13 for ATX
and as high as 0.60 for MPH (56)], although eects on ADHD
symptoms are larger and more consistent than for executive
function or reading (56, 116). Future work in this area should
investigate the impact of these and other medications on RD with
other commonly co-occurring conditions, as well as examine the
neurophysiological mechanisms of these treatments in comorbid
groups.
Experimental Interventions
Initial research suggests that neurofeedback training to increase
attention processes (118, 119) may be eective in reducing
ADHD and RD symptoms, although investigations of these
brain-based interventions are too preliminary to be fully
endorsed as treatments for RD. Altering cortical excitability using
neuromodulation techniques, transcranial magnetic stimulation,
and transcranial direct current stimulation is shown to change
reading and reading-related abilities in typical and RD adults
and children, though parameters such as stimulation frequency
and location are not consistent in their benets (120, 121). ese
studies have not investigated neuromodulation with RD and
comorbid conditions and are still in experimental and proof-of-
concept stages.
CLINICAL IMPLICATIONS AND
SIGNIFICANCE
Knowledge and awareness of RD are highly relevant to health-
care professionals working with children, as mental disorders
may be comorbid or blended, and RD can be overlooked or
undertreated. Evidence for the co-occurring disorder may be
recognized before the RD is identied (e.g., ADHD and ASD),
may follow the RD (e.g., depression), or may be intertwined
with RD (e.g., anxiety and behavioral disorders). In all of these
co-morbidities, the mechanisms of the disorders may overlap,
and more research is needed to identify the mechanism of
the overlap, the sequencing of their developmental and neu-
rodevelopmental inuence, the most benecial targeting and
nature of interventions, and the economic burden of RD with
and without treated and untreated comorbid mental disorders.
Although one disorder may be identied as the primary target
for intervention, comprehensive interventions should address
both the RD and the comorbidity to produce optimal treatment
results.
AUTHOR CONTRIBUTIONS
RH designed the article and wrote the Sections “Introduction”
and “Treatment.” RH and SH cowrote the Comorbid Mental
Disorders sections—SH also constructed the table. JB wrote
the Section “Socioemotional Health.” NW wrote the Section
“Reading Interventions.” FH wrote the Section “Overview of RD”
and added to all sections. All the authors read and approved the
paper.
FUNDING
RH was supported by research grants from Curemark,
BioMarin, Roche, Shire, Sunovion, Autism Speaks, and
Vitamin D Council and is on the Advisory Board for Curemark,
BioMarin,Neuren, and Janssen. FH was supported by grants
from the Eunice Kennedy Shriver National Institute of Child
Health and Human Development (NICHD) R01HD078351,
R01HD086168, R01HD065794, P01HD001994, National
Science Foundation (NSF) NSF1540854,Oak Foundation Grant
ORIO-16-012, University of California Oce of the President
Multi-campus Research Program (MRP-17-454925), and the
Potter Family. JB was supported by an Ignite Award, Boston
College.

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Frontiers in Psychiatry | www.frontiersin.org March 2018 | Volume 9 | Article 101
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