LAUSR

Neurodevelopmental disorders are conditions that involve early insult or abnormality in the developing central nervous system and are associated with a wide spectrum of abilities. These conditions begin during the early developmental period (usually conceptualized as prenatally though the first 3 years of life), affect day-to-day functioning, and are often lifelong. Because the “typical” development of the nervous system has been altered in individuals with neurodevelopmental disorders, reorganization and competition for function occur, usually resulting in skill patterns that are less efficient than among individuals without such conditions. The timing of these alterations or developmental disruptions is also relevant, as different neural systems are selectively vulnerable to injury at different phases of prenatal and post-natal development. As a result, the behavioral and cognitive dysfunction associated with early neural damage can range from subtle (or absent) to diffuse and profound. Moreover, the functional impairments can be observed immediately in some individuals, while in others, the full range of deficits may not manifest until later in life, even though the neurobiological basis of the condition is present earlier (Rudel, 1981). Among children with neurodevelopmental disorders, the trajectory is often “off developmental track” relative to the trajectory of typically developing children. Developmental delays (i.e., patterns of skill development that should have occurred earlier in life) are often observed early in life. While functional catch-up is possible, it is often incomplete, and the resulting maturational timelines based on typical development become less applicable (Mahone, Slomine, & Zabel, 2018). Neurodevelopmental disorders are highly prevalent. Recent estimates from the Centers for Disease Control and Prevention (CDC) in the United States show that around one in six, or approximately 17%, of children ages 3 through 17 years have one or more neurodevelopmental disabilities (Boyle et al., 2011). The rates also are increasing, and the CDC reports may underestimate the actual prevalence worldwide. In the past 25 years, medical advances have improved the life course of several genetic, medical, and neurodevelopmental conditions, making them more survivable and compatible with life (e.g., very low birth weight preterm infants, congenital hydrocephalus) and extending the expected lifespan of others (e.g., cystic fibrosis, sickle cell disease). Due to higher survival rates and lifespans extending into adulthood, increased attention has been given to the development of selfmanagement and independence skills and the transition into older adolescence and young adulthood (Tarazi, Mahone, & Zabel, 2007; Warschausky, Kaufman, Evitts, Schutt, & Hurvitz, 2017; Zabel, Jacobson, & Mahone, 2013). Given these considerations, the assessment and study of individuals with neurodevelopmental disorders is of significant interest to neuropsychologists. Classification of neurodevelopmental disorders can be conceptualized using two primary approaches, one emphasizing behavior (without explicit reference to etiology), and the other emphasizing etiological medical, genetic, and neurological factors (Mahone et al., 2018). In the field of neuropsychology, those neurodevelopmental disorders defined on the basis of behavior (including attention-deficit/hyperactivity Disorder, ADHD; learning disabilities, LDs; autism spectrum disorders, ASDs; and intellectual disability, ID) have received considerable emphasis, in part because of their prevalence and overall public health relevance (Leigh & Du, 2015; Mahone & Denckla, 2017; Mahone & Mapou, 2014). Neurodevelopmental disorders diagnosed on the basis of known or presumed medical etiologic factors have received somewhat less emphasis among neuropsychologists. Such conditions include those with genetic, environmental (injury, infection, teratogens), or multi-factorial medical etiologies. This special issue of the Journal of the International Neuropsychological Society focuses upon such conditions with known medical or genetic etiologies, and includes 11 papers presenting innovative and novel data related to the neuropsychology (including identification of biomarkers) of specific neurodevelopmental disorders. Included in the issue are seven studies reporting new empirical findings, two critical reviews, and two case reports. The timing of this special issue follows on the heels of the 50th anniversary of the implementation of US PL-88-164 (“Mental Retardation Facilities Construction Act”), which, in 1967, provided