Special Issue on Developmental Delay

A great proportion of the practitioner's time is spent on examination and treatment of children with developmental delays (DD). This condition can be specific (SDD) and hence restricted to a single developmental domain, yet it is more often global, covering two developmental domains or more. Global developmental delay (GDD) refers to infants and preschoolers, ages 0–5 years, who present with persistent delays of six months or more, in two or more of the following developmental domains: gross/fine motor, speech/language, cognition, social/personal, and daily living activities. Cognitive delays are often present, yet typically, in most cases none of the impaired areas is dominant enough to constitute the prime diagnosis. Performance in the impaired domains is two or more SD below the mean, where standard tests are available (Francoeur et al., 2010). The prevalence ofSDD varies according to the domain, whereas GDD affects 1–3% of children.

Following initial diagnosis and as the child matures, in most cases GDD will be substituted with a specific diagnosis that can account for the condition. These often signal lasting impairments. Thus, although short-lived, the term developmental delay, whether global or specific, may create a misleading diagnostic impression, for delay implies catching up, whereas for a large proportion of the children diagnosed with DD in infancy, a lasting impairment is likely to be present (Shevell, 2010).

Problems with the term DD have been repeatedly pointed out. Recently, Williams (2010) highlighted the lack of consensus in the use of DD and suggested that terms such as “specific,” “mixed,” or “pervasive” delays in reference to specified domains, may be more useful. An International Consensus Conference set up in 2008 and followed up in 2009 proposed a substitute term—“Early Developmental Impairment,” signaling a condition of the early years that is not better explained by another established diagnosis. Note the substitution of the term “delay” which leaves open the possibility of a transient condition, with the term “impairment”, suggesting a permanent disability. The diagnosis of “early developmental impairment” further specifies that reassessment is due by school age, definitely before the age of 9, to determine whether the child's condition is not better explained by a specific diagnosis.

Several roadblocks to applying the term “impairment” rather than “delay” were noted in countries where a variety of economical, medical, and cultural conditions hold, and practices differ from those common in Western countries. Furthermore, given a Western perspective, one may still question the use of the term “impairment” in cases which may turn out as genuine instances of “delay.”

Children with GDD are often considered as appropriate controls in studies that focus on specific disabilities. The underlying assumption is that the heterogeneity of this group will cancel out potential biases. This hypothesis depends on the lack of partiality in assigning this diagnosis, as well as on exclusion of children whose profiles may overlap with that of the main study group.

This special issue examines the term “developmental delay” from various perspectives, reviewing etiologies as well as clinical and research uses of the term. Atypicalities in the relevant domains are presented and the existence of unique, within-domain profiles that might predict specific outcomes as the child matures are considered. The predictive power of GDD and the specificity of SDD in the young child are important underlying themes in all the articles.

The first set of papers concerns common etiologies of DD. Diav-Citrin reviews the effects of prenatal exposure to infectious agents, substances of abuse, and physical factors on the development of the human embryo, and discusses possible mechanisms of neurobehavioral teratogens. Ergaz and Ornoy review perinatal events involving mother and fetus during delivery that can result in DD. The paper reviews neonatal conditions that require immediate intervention, suggesting that early and accurate evaluation can predict outcome and direct medical decisions.

Prematurity is a risk factor for DD and disabilities. Sansavini, Guarini, and Caselli review the developmental pathways of preterm infants and consider impairments as well as DD brought about by prematurity. The term developmental delay is considered within a dynamic approach that focuses on the process of change emerging from interaction of neurobiological, physical, and socio-environmental factors.

Tirosh and Jaffe focus on GDD and mental retardation (MR). They review studies concerning the genetic etiologies of MR discussing the pediatric perspective and highlighting assessment, family role, and the general structure of management of the child with GDD/MR.

Given these common etiologies and general profiles, the next set of papers focuses on specific developmental domains. Zuk reviews evidence suggesting that spontaneous general movement (GM) in the term, preterm and young infant at risk is a valid method of assessment of neurological status. Age-related qualitative changes in GM reflect brain development and maturation and can serve as the basis for predicting developmental outcome. Zuk reviews studies showing that GM is particularly sensitive to the detection of cerebral palsy (CP), the latter being the most predominant physical disability within the spectrum of developmental delay.

McIntyre, Walker, Morgan, and Novak review the literature relating to three distinct groups of children with CP—the premature infant, infants born at term with neonatal encephalopathy, and the numerically largest group, consisting of term infants who appear to have no identifiable risk factors for CP. McIntyre and colleagues suggest clinical pathways within CP that include assessment, treatment, and expected outcome.

Language is a primary area calling parents’ and clinicians’ attention to a child's developmental status. What characterizes specific language impairment (SLI)? How specific is it and does it predict a child's later language competence? Rescorla suggests ways of characterizing groups within what is referred to as “late talkers.” Research suggests that when language delay is the primary condition affecting the child, the rate at which children catch up differs and some late talkers continue to manifest language problems well into middle childhood. Stokes and Klee argue that a multifactorial model of language development is essential to increase accuracy of prediction in cases of language delays. They examine the literature in relation to theoretical models of learning, offering a new framework for characterizing early language delay.

Autism spectrum disorder (ASD) has variable presentations and early symptoms differ within the spectrum. Nevertheless, in recent years there have been dramatic advances in the identification of the early signs of ASD and its differentiation from other developmental pathologies, specifically GDD and SLI. Luyster, Seery, Thompson, and Tager-Flusberg review the literature on risk signs in the first two years that predict the nature and severity of language impairment in children with ASD or SLI. The sensitivity and specificity of multiple behavioral and neurobiological factors predicting these conditions are considered.

Mitchel and Zwaigenbaum review studies of young children with autism, focusing on social-communication, temperament, motor function, and language behavior. Based on a review of the literature, the authors suggest candidate markers that will distinguish DD that are characteristic of children with ASD from those that characterize children with other pathologies.

Attention deficit hyperactivity disorder (ADHD) accompanies many, perhaps most, of the neurodevelopmental disabilities and is particularly evident as the child enters formal schooling. Berger and Nevo describe early cues and risk factors present already in the preschool years. They provide a developmental perspective, offering new directions for research, early detection and intervention in young children with ADHD.

In the summary article, Levy, discusses the term GDD as it is applied in clinical contexts. Levy considers the domains covered in the articles, grappling with the question of early decomposition of GDD into unique developmental profiles that underlie specific disabilities. Levy discusses the significance of chronological age as it is revealed in recent neurobiological research, with an emphasis on the three way interaction between genes-age-environment and the notion of sensitive period in development. The gains as well as drawbacks to clinical and research practices likely to accrue from a decomposition of the term GDD, as it meets the complex reality of the developing child, are discussed.