According to the latest revised version of the Statistical Manual of Mental Disorders (1) which coincides with the DSM-5 (2) neurodevelopmental disorders (NDs) would be those that include a clinical manifestation in almost all developmental domains. These are intellectual disability (ID), as well as those that affect more specific domains, such as attention deficit/hyperactivity disorder (ADHD), autism spectrum disorder (ASD), communication disorder (CD), specific learning disorder (SLD, including difficulties in reading, writing and mathematics), and motor skills disorder (MD, such as Tics, Tourette and stereotypic disorders), among others (3). See Table 1.
Table 1
Neurodevelopmental Disorders (DSM 5; Diagnostic and Statistical Manual of Mental Disorders. 5th ed) Note: Before each disorder name, the ICD-9-CM code is indicated followed by the ICD-10-CM code in parentheses. Blank lines indicate that the ICD-9-CM or ICD-10-CM code is not applicable.
__-_ (__. _) INTELLECTUAL DISABILITY (Intellectual Developmental Disorder) (17) According to current severity: - 317 (F70) Mild - 318.0 (F71) Moderate - 318.1(F72) Severe - 318.2 (F73) Profound 315.8 (F88) GLOBAL DEVELOPMENTAL DELAY (23) |
COMMUNICATION DISORDERS (24) 315.32 ( F80.2) LANGUAGE DISORDER (24) 315.39 ( F80.0) Speech Sound Disorder (Phonological Disorder) (25) 315.35 ( F80.81) Childhood-Onset Fluency Disorder (Stuttering) (25) 315.39 ( F80.89) Social (Pragmatic) Communication Disorder (26) |
AUTISM SPECTRUM DISORDER (28) 299.00 ( F84.0) Autism Spectrum Disorder |
ATTENTION DEFICIT HYPERACTIVITY DISORDER (33) __._ (__-_)Attention deficit hyperactivity disorder (33) Specify if: 314.01 (F90.2) Combined presentation 314.01 (F90.0) Predominantly inattentive presentation 314.01 (F90.1) Predominantly hyperactive-impulsive presentation |
SPECIFIC LEARNING DISORDER (38) (__-_) (__._) Specific learning disorder (38) Specify: 315.00 (F81.0) With impairment in reading 315.2 (F81.81) With impairment in written expression 315.1 (F81.2) With impairment in mathematics |
MOTOR DISORDERS (41) 315.4 (F82) Developmental Coordination Disorder (41) 307.3 (F98.4) Stereotypic Movement Disorder (42) Tics disorder 307.23 (F95.2) Tourette's Disorder (43) 307.22 (F95.1) Persistent (Chronic) Motor or Vocal Tic Disorder (44) 307.21 (F95.0) Provisional Tic Disorder (44) |
NDs usually begin in childhood, although most of them are chronic and persist for life. This new approach is committed to the inclusion of NDs within a heterogeneous and dimensional group, leaving behind the categorical classifications of the DSM 4th edition (4) and the International Statistical Classification of Diseases and Related Health Problems (5). The new edition of the ICD (ICD-11) unifies its criteria with those of the DSM-5 (2013). Finally, DSM-5 revised (i.e., DSM-5-TR) has just been published in 2022.
To our knowledge, there are only a few studies in the scientific literature that measure the prevalence of NDs according to DSM-5 criteria (2013) in minors. Reported prevalence rates in 2022 were as follows: intellectual disability (ID), 0.63%; attention deficit/hyperactivity disorder (ADHD), 5–11%; autism spectrum disorder (ASD), 0.70-3%; specific learning disorder (SLD), 3–10%; communication disorders (CD), 1-3.42%; and motor disorders (MD), 0.76-17% (6), (7), (8), (3), (9), (10), (11).
Among the available literature, prevalence studies and meta-analyses are the most frequent. The prevalence rates of the most common NDs were estimated as follows: ADHD = 7.9–9.5% (12), (13); SLD = 0.7–2.2% [ (14); (12); (15)]; SLD (or developmental dyslexia [DD]) = 1.2–24% [ (16); (17)]; and motor coordination disorder = 1.4–19% [ (18); (19)]. Furthermore, reported prevalence rates for various disorders within the same study did not include coexistence rates between disorders (10).
In the United States, according to data published by the National Center for Health Statistics (NCHS) in 2015, it is estimated that NDs affect 15% of children between the ages of 3 and 17 (20).
In a previous systematic review by our research team (3), we found that the global prevalence rate of NDs fluctuates globally between 4.70% in Scotland (8), 55.5% in Norway (9), and 88.50% in Japan (10).
These variations depended on methodological aspects, such as estimation procedures and sociocontextual phenomena. The criteria used by the different studies varied, and the processes used to measure the indicators were often not made explicit. There was also little direct evaluation and, consequently, little diagnostic certainty in the clinical population. Furthermore, studies often did not consider the complexity and comorbidities of the disorders; instead, symptoms or risks tended to be analyzed individually. Secondary sources are important as complementary resources for diagnosis, but prevalence studies with direct sources are lacking. Among the few studies where it is directly assessed, we find that in the study of Catalonia (7) and Norway (9), clinical diagnostic measures and questionnaires that assess symptoms through teachers are used. The Japan study (10) uses surveys and questionnaires through parents and teachers. Most prevalence studies use indirect estimates such health database records that are likely to be less accurate.
NDs are usually underdiagnosed (21). Therefore, children who have not been diagnosed are more likely to suffer from emotional and behavioral problems, low self-esteem, lower than expected academic performance, difficulties in social relationships, unemployment, delinquent behavior and functional impairment (22), (23). The implementation of early detection and early intervention programs is essential (24).
NDs usually present homotypic comorbidity, and it is rare that they occur in isolation. Despite this, there is a large body of literature on specific disorders, and they have rarely been evaluated as a whole.
Multimorbidity among NDDs is the norm, as determined in Japan (10), low-resource countries (6), Scotland (8), Spain (11), and Norway (9). The prevalence of NDDs seems to remain stable over time in different cultures, ages, ethnic groups (25) socioeconomic strata, types of community (rural or urban), and religions (26). Gender differences in NDDs are consistent, with males being the most affected by general psychiatric psychopathology, as reflected in the contributions in Scotland (8) and Denmark (27).
Males are more affected in NDs; 66.3% of the children included in the cross-sectional study in Norway (9) were male, and in a sequential cross-sectional study in Japan (28) a male:female ratio of 2.2:1 was reported. With regard to ADHD, male:female ratios of 4:1 and 2:1 have been determined in a systematic review and meta-analysis in Spain (29),(30), generally coinciding with the reported ratios (3 − 2:1) in the systematic reviews by Sayal et al. (2018) and Faraone et al. (2021). Finally, in children with ASD, a male:female ratio of 4.5:1 was reported in a retrospective analytical cohort study (31).
Considering the variations in prevalence found in the different studies analyzed worldwide, we considered it necessary to carry out more studies in nonclinical samples and with direct evaluations that better reflect the reality of the population. In Catalonia (7) and the USA (32), a study was done through a school sample, in Galicia (11), in Catalonia (31), in Norway (9) and in Brazil (33), a study of a clinical sample of children attended in specialized mental health services was done.
In countries with low socioeconomic resources (6), such as China (34) and Japan (10), a sample of the general population (rural and urban) was obtained. For this reason, we decided to conduct this study in a primary care sample, which we thought would more accurately reflect prevalence risk approximations than in clinical samples. The age of 6 years was decided to insist on early detection and to demonstrate that it is possible to carry out an intervention from secondary prevention and take advantage of early ages where neuronal plasticity can still be used even if at age 6 only the most severe forms of learning risk problems are expected to be detected. Due to the heterogeneity of these disorders, the fact of choosing 6 years of age limits us to diagnose the most severe cases of ASD or ID that would be detected before 3 years of age. Even so, we have observed an under-diagnosis of the more subtle forms and with better IQ. This is the first study in school age where an exhaustive and direct assessment is carried out by professionals trained in neurodevelopment in a population sample.
The objectives of this study were to measure the risks of presenting any neurodevelopmental disorder according to DSM-5 (that is, ADHD, ASD, SLD, MD and CD) and their possible comorbidities to later be validated in a second phase of neuropsychological and clinical assessment in the Specialized Mental Health Unit with the altruistic collaboration of a psycho-pedagogical center and with the support of a clinical team trained in all the evaluation and research tools.