The Bayley Scales of Infant and Toddler Development, Third Edition (Bayley-III; Bayley, 2006), developed by Nancy Bayley, assesses developmental functioning of children between 1 and 42 months of age. The Japanese version of the Bayley-III is still being developed. The Bayley-III is also designed to measure the strengths and weaknesses of a child in the five developmental areas of cognition, language, social-emotional, motor and adaptive behaviour. A tester gives tasks of three parts (cognitive, language [receptive communication and expressive communication] directly to a child, and motor [gross motor and fine motor]). The tester also asks caregivers about two child developmental areas (social-emotional and adaptive behaviour). The Bayley-III can be administered in approximately 50–90 min.

Scoring is showed as a score profile based on the five developmental areas of cognition, language, social-emotion, motor and adaptive behaviours. A total score is not provided, because a goal of the Bayley-III is to promote understanding of a child’s strengths and weakne sses in the five developmental area s.

The Kyoto Scale of Psychological Development (K-Test), developed by The New Version of the Kyoto Scale of Psychological Development Society, is one of the most widely used developmental assessments for the toddler and preschool stages in Japan (Kyoto Scale of Psychological Development Society, 2008) (see Fig. 20.1). The K-Test is standardised for 2677 Japanese infants and adults. The tool mainly assesses children’s developmental progress, delay, and balance. The K-Test is based on Gesell’s developmental diagnosis and refers to the Binet test. The K-Test assesses developmental and intelligence levels from infants to adults, and usually targets infants with developmental disorders and adults having no language in Japan. The utility of the K-Test is examined by the cognitive assessment of 74 children with ASD (Koyama, Osada, Tsujii, & Kurita, 2009). The K-Test developmental quotient (DQ) and the three subscales showed high correlation with the Tanaka-Binet Intelligence Scale IQ.

The K-Test consists of a series of individually administered tasks. A psychologist gives the tasks directly to children for the assessment of their development. The K-Test uses a developmental age (DA) for psychological development. A DA over a chronological age yields a DQ ratio. Also, both DA and DQ are calculated in a full scale and three subscales (postural-motor (P-M), cognitive-motor (C-M), and language-social (L-S)) (see Fig. 20.2). The K-Test can be administered in appr oximately 30 min.

The Tanaka-Binet Intelligence Scale, a modified Binet test by Tanaka, assesses the intelligence and cognitive abilities in individuals from children to adults. The Tanaka-Binet Intelligence Scale is also called the Japanese version of the Stanford-Binet Intelligence Scale (Tanaka Institute for Educational Research, 2003). The Tanaka-Binet Intelligence Scale, Fifth Edition (TB Scale-V) is the current version used in Japan. The TB Scale-V, as well as the Wechsler Intelligence Scale, the most popular standardised intelligence test in Japan, is useful for testing individuals who have limited language abilities. A full IQ is obtained by a mental age over a chronological age ratio. For people under 13 years of age, IQ is calculated based on the chronological age. For people over 14 years of age, TB Scale-V measures deviation IQ for four factors of cognitive abilities [(1) crystallised IQ, (2) fluid IQ, (3) memory, (4) logic and rational faculty]. The TB Scale-V can be administered in approximately 30 min.

The items of TB Scale-V are shown in Table 20.2. In TB Scale-V, subjects start with items of an age-equivalent level. When a subject fails a task of the age-equivalent level, he or she is asked to answer tasks of a lower age-equivalent level until he or she passes all tasks of a specific age-equivalent level. Then, he or she is asked to answer tasks of higher age-equivalent levels until he or she fails all tasks of another specific age-equivalent lev el.

The Wechsler Intelligence Scale for Children-Fifth Edition (WISC-V), developed by Wechsler, is an individually administered instrument for assessing cognitive ability in children (Wechsler, 2003) from age 6 to 16. The Japanese version of the WISC-V is still under development. The result based on profile of the WISC-V could serve as a tool in appropriate treatments and educational guidance. The WISC-V has two formats (traditional paper and pencil and digital version on Q-interactive). Also, the WISC-V is faster and easier to administer than the WISC-IV due to such factors as reduced testing time to obtain a full-scale IQ.

The WISC-V yields a full-scale IQ and five primary index scales [(1) verbal comprehension, (2) visual spatial, (3) fluid reasoning, (4) working memory, (5) processing speed], five ancillary index scales, and three complementary index scales (see Fig. 20.3). The WIS C-V can be completed in approxi mately 45–60 min.

The Wechsler Adult Intelligence Scale is one of the most widely used behavioural tests to examine cognitive profiles of adults in the world; it has been translated into many languages. Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV) is a new version of the Wechsler intelligence test for adults. The Japanese version of WAIS-IV is under development. The purpose of WAIS-IV is for educational planning and the support of job skills. WAIS-IV has two formats (traditional paper and pencil and web-based on Q-interactive).

WAIS-IV has Full IQ [FIQ], 4 index scales [(1) verbal comprehension, (2) perceptual reasoning, (3) working memory, (4) processing speed] and 15 subtests (10 subtests and 5 supplemental s ubtests) (see Fig. 20.4).

Research on ASD is one of the most widely funded areas in many parts of the world. Advances in fundamental research in neurological science (e.g. brain circuits and dynamic processes in individual brain development, functional connectivity), genetics, epigenetics, gene–environment interactions and environmental risk factors all aim to interpret the causes of autistic symptoms and find connections to other causes that occur with non-autistic symptoms. Social information processing, lack of a theory of the mind, neurocognitive function and intellectual attribution bias, underconnectivity in neural systems, unconventional sensory information processing, level changes in motivation and social attention are the most researched diagnostic domains of ASD (Happe, 1994; Scheuffgen, Happe, Anderson, & Frith, 2000; Williamson & Jakobson, 2014; Yirmiya, Solomonica-Levi, Shulman, & Pilowsky, 1996).

Presently, ASD and ID are the most common (approximately 3–5 %) developmental disorders in the human population. Many of the new research methods on ASD and ID seek to isolate specific brain circuits that could cause disrupted brain functions related to social and cognitive impairment in neurodevelopment. The presence or absence of ID is considered to be one of the most critical factors affecting developmentally related outcomes in individuals with ASD (Henninger & Taylor, 2013; Howlin, Goode, Hutton, & Rutter, 2004). It is a widely accepted view that ID co-occurs in approximately two-thirds of persons with ASD (Thomas et al., 2014). ASD and ID are both complex and multifactorial neurodevelopmental disorders with high heritability, and they share overlapping risk factors (Betancur et al. 2009). The development and recent advances in aetiology, functional brain scanning (fMRI) and developmental neuroscience all show the importance of early social experiences for cognitive development and intellectual/developmental functioning (Amaral et al. 2008).

ID is characterised by significant limitations in intellectual functioning and adaptive behaviour . ID might occur as an isolated developmental disability problem or be accompanied by impairment in sensory processing development, epileptic seizures and behavioural disturbances. During childhood (before the age of 18 years), adaptive behaviour and intellectual functioning strongly contribute to the development of conceptual, social and practical adaptive skills (Schalock, 2011). Recent research results show that ID in ASD might emerge as a consequence of severe social-communication deficits on the experience-dependent mechanism underlying various neurocognitive developments. The study results of Vivanti, Barbaro, Hudry, Dissanayake, and Prior (2013) suggest that ASD symptom severity contributes to the extent to which environmental input is required to support typical brain development . This study states that the risk of developing ID increases as the number and severity of ASD social-communicative impairments increase (Vivanti et al., 2013).

There are two main conceptual frameworks related to the nature of ASD-ID/ID-ASD association. One is the so-called “co-morbid condition theory ”, which states that ID is a co-morbid condition that occurs over and above the ASD symptoms (Matson et al., 2011; Matson & Williams, 2014). The explanation behind the “co-morbid condition” emphasises the unrelated causality and unrelated aetiology. Thus, the co-morbid condition and/or symptoms are conceptually distinct from the principal diagnosis.

The second concept is the so-called “distinct additional theory ” that suggests the aetiological relationship between ASD and ID. Some researchers think that there are common aetiological factors that could cause ASD and also cause ID (Waterhouse, 2013). Waterhouse (2013) states that the aetiological background of ASD is too broad to be sure of anything, and she uses a metaphoric “illusive butterfly” to explain that 30 years of tremendous research could not give any “certain” answer to the aetiological concept of ASD, and every “new door” that science opens up provides us with the access to another that needs to be opened.

Developmental theory-dominated clinical neuropsychology research emphasises that the early neurocognitive development of the human brain is experience-dependent by nature (Karmiloff-Smith et al. 2002). Therefore, unbalanced and insufficient early social experiences could cause an inadequate cognition of self- and peer awareness by proxy, and result in an adverse impact on cognitive brain functioning (Makinodan, Rosen, Ito, & Corfas, 2012). Many of the recent ASD- and ID-related studies focus on the best possible early detection and early intervention in order to be able to provide (e.g. design, develop, arrange, modify) the necessary social and physical environment for psychosocial and cognitive development for children at high risk of developmental delay or disability (Toth, 2010). Structured early intervention programmes and development therapies could make a difference in sensory processing, sensorimotor development and speech-language abilities (Gernsbacher, Sauer, Geye, Schweigert, & Hill Goldsmith, 2008). Developmental delay and impairment in the communication and speech domain could be the secondary results of the ID and/or ASD symptoms (Dziuk et al., 2007). If a child during the early “sensitive developmental period” does not have or cannot respond well to early sensory and social inputs from the closed physical and social environment, then he or she will not be able to demonstrate adequate adaptive responses and will show signs of either ID, ASD or both (Klin et al. 2014; Travers, Kana, Klinger, Klein, & Klinger, 2014; Ventola, Saulnier, Steinberg, Chawarska, & Klin, 2014). Researchers of experience-dependent neurocognitive development emphasise that, in the case mentioned above, ID is not a co-morbid condition, but rather is the ultimate result of an inefficient functional brain development. In this case, the severe ASD symptoms could be found responsible for the developmental delay of intellectual development and cognitive functions. This does not mean that ASD could necessarily cause ID, but emphasises the fact that severe ASD symptoms cause an at-risk situation for intellectual developmental delay (Gotham et al. 2012; Grossmann & Johnson, 2007).

ASD core symptoms appear in the social communication and interaction domain of development and atypical patterns of behaviour (restricted and repetitive) and interest (Wilkins & Matson, 2009). Symptoms of ID usually group into two main diagnostic categories. The first is called intellectual functioning. It includes delayed cognitive information processing and altered development of basic intellectual skills, abilities, and virtues. The second is called adaptive functioning. It includes conceptual skills for learning (e.g. language, literacy, mathematics), social skills (interpersonal relationships) and practical skills related to self-care, health and safety. Many researchers have questioned the presence of ID in the case of children with ASD, for several reasons (Kraijer, 2000; Matson et al., 2013). One of these reasons is the reliability or unreliability of intelligence scales used to assess the IQ of children with ASD. Certain limitations make testing difficult for a child with ASD. Scheuffgen et al. (2000) state that a child with ASD might not be able to complete intellectual measurement tests. For instance, if a child with ASD has moderate or severe speech and/or language difficulty, the child may not be able to respond to interview questions (Scheuffgen et al., 2000). Another difficulty is that in most cases, the diagnosis of ASD symptoms in children with ID is based on clinical criteria validated for populations with average intelligence, thus compromising the diagnostic accuracy of ASD criteria (Javaloyes, 2006). Certain verbal subtests show low performance, while others like block design show superior performance results (Shah & Frith, 1993). A person with ASD could have one or a set of special abilities called savant skills. These are areas of surprising talent in otherwise low-functioning individuals. The estimated prevalence of savant abilities in autism is 10 %, whereas the prevalence in the non-autistic population is less than one percentile. The most common forms of savant abilities involve mathematical calculations, an extraordinary memory, musical abilities (with perfect pitch and excellent musical memory), and other types of artistic abilities (e.g. drawing, painting, singing, playing an instrument). A mathematical ability that many autistic individuals display is calendar memory, while others can multiply and divide large numbers without w riting them down and can also calculate prime numbers in their heads in only seconds (Frith, 1993).

Research on ASD and ID co-morbid features concludes that the severity of ASD symptoms should be independent and separately measured from the severity of cognitive functioning and intellectual abilities. A longitudinal study with 345 participants documented that ID is a distinguishable part of the whole disability feature in children with severe ASD symptoms, but less in cases with mild ASD symptom representation; thus, cognitive functioning and ASD symptom severity are not entirely independent features (Gotham et al., 2012). Another study by Vivanti et al. (2013) targeted this latest hypothesis by developing an intervention programme that aimed to improve ASD symptoms. Vivanti and colleagues predicted that children with severe ASD symptoms are likely to have lower intellectual ability. Therefore, if these children receive a targeted therapy programme for their ASD symptoms, they should have improved results in intellectual skill development as well. They based their intervention on recent results in developmental neuroscience that support the “experience-dependent” nature of early brain development (Kuhl, 2007). Positive changes in intellectual functioning could be gained from early behavioural interventions, even if the original aim was to weaken core ASD symptoms. Early appearance of social-communication difficulties in children with ASD could result in sensory processing disorder and cause an unintentional neuropsychological “block” against receiving essential inputs from the closed environment, thus negatively affecting cognitive skill development (Schoen, Miller, Brett-Green, & Nielsen, 2009). These results suggest the possible interdependent relation between ASD and I D (Vivanti et al., 2013).

Neurodevelopmental disorders like ASD, ID and Attention Deficit Hyperactivity Disorder (ADHD) are complex traits that are influenced by more than one factor (genetic or environmental); multiple genetic determinants interact in the context of poorly understood environmental factors to give rise to clinically diverse phenotypes. Research results from genetic, epigenetic and environmental studies seek to identify candidate genes that could cause ASD, ID and ADHD and contribute to the understanding of these conditions from the comparative pathobiological viewpoint (Ben-David & Shifman, 2012; Betancur et al., 2009; Kou, Betancur, Xu, Buxbaum, & Ma’ayan, 2012). These molecular- and cellular-based results could contribute to possible therapeutic approaches in the future. From the genetic standpoint, ASD and ID are likely to be related on the molecular and biochemical level. The genetic approach sees the causal factors of ASD and ID as both similar and in many ways very different in nature. On the one hand, an estimated 70 % of diagnosed ASD individuals have some level of ID as well, while the others have dysfunctions in speech-language and communication, as well as difficulties in cognitive and social behavioural areas. On the other hand, at least 10–15 % of persons with ID diagnosis have autistic tendencies or clearly identified ASD symptoms (Mefford, Batshaw, & Hoffman, 2012). A number of genetic syndromes manifest ASD at higher than expected frequencies compared to the general population. Recent results from various genetic studies reported that no single gene could be signific antly associated with ASD, and there is a high possibility that gene mutation and hundreds of gene variants might be responsible for causing the ASD condition (Anney et al., 2012; Liu et al., 2013). A large number of these gene variants and mutations could be associated with either ASD or ID, while some (e.g. SHANK1, SHANK2, NRXN1) are found to be associated with both conditions (Berkel et al., 2010; Sato et al., 2012). Kou et al. (2012) used systems biology and a combined network approach to predict candidate genes for ASD and ID. Their results showed that ASD and ID share common pathways that could perturb (i.e. alter the regular state or path of) an overlapping synaptic regulatory sub-network (Kou et al., 2012).

During the last 10 years, significant progress has been made in identifying rare variants of major effect in both ASD and ID; however, it is still difficult to find the best possible explanation for the underlying molecular mechanism of high-risk family traits and rare inherited mutations (Srivastava & Schwartz, 2014). As a result of extensive worldwide genetic research related to specific genetic causes, science now has identified many individually rare genes that could be associated with a high risk for ASD, and some of them extensively overlap with genes for ID. A particular genetic aetiology can currently be identified in about 15 % of patients with ASD (van Bokhoven, 2011). Presently on-going studies estimate that in the future 60–80 % of ASD-ID genes and “loci” (position of a gene or mutation on a chromosome) remain to be discovered, and hundreds of genes would be identified to be causally associated with these conditions (Topper, Ober, & Das, 2011). The California Autism Twins Study (CATS) reported research results on 192 identical and fraternal twin pairs. The research study reported a concordance rate of 77 % for male monozygotic twins and 50 % for female identical twins. The rates amo ng fraternal twins were 31 % (male) and 36 % (female) (Hallmayer et al., 2011).

Although the high correlation between autism and genetic factors has been long established, the exact genetic background of ASD remains unclear. Some of the new findings turned out to be mere chance associations, and were reported by studies because they looked significant at the time. There is a regular line of new studies reporting on possible associations between recently identified genetic conditions and ASD. Zafeiriou, Ververi, Dafoulis, Kalyva, and Vargiami (2013) reported ASD as a heterogeneous group of neurodevelopmental disabilities with various aetiologies, but with a heritability estimate of more than 90 % (Zafeiriou et al., 2013; Zafeiriou et al. 2007). Their study concludes that it is essential to identify ASD in patients with genetic syndromes , in order to ensure correct management, future therapeutic approaches and appropriate educational placement.

Findings from the study of genetic syndromes are incorporated into the ongoing research on autism aetiology and pathogenesis. Different syndromes converge upon common biological backgrounds (such as disrupted molecular pathways and brain circuitries), which probably account for their co-morbidity with ASD (Zafeiriou et al., 2013).

There are well-known syndromes and conditions that could cause ID and/or ASD as well. It is estimated that these syndromes account for more than 10 % of ASD cases. These syndromes include fragile X syndrome, Down syndrome, Prader–Willi syndrome, Williams syndrome, Angelman syndrome, Duchenne syndrome, etc. This chapter gives a short research summary on the first three in connection with ID and ASD.

Fragile X syndrome is an inherited g enetic disease that causes ID and could cause developmental disabilities as well. Fragile X syndrome is found in about 1 in every 4000 males and about 1 in every 8000 females. Fragile X syndrome is the most common hereditary source of ID in men. People with fragile X syndrome may show a combination of the following signs as children and throughout life: anxiety (general or social), ASD like symptoms (e.g. social problems, such as not making eye contact, disliking being touched, trouble understanding body language), ADHD-like symptoms (e.g. impulsiveness, attention problems, hyperactivity), epileptic seizures and sleeping disorders. Nowadays, fragile X syndrome is recognised as the most common identifiable genetic cause of ID and ASD, with many overlapping phenotypic features (Yu & Berry-Kravis, 2014).

Another well-known syndrome that could cause ID and sometimes ASD co-morbidity is Down syndrome . There has been an increase in the number of children with Down syndrome who are being diagnosed as having ASD as well (Gray, Ansell, Baird, & Parr, 2011; Starr, Berument, Tomlins, Papanikolaou, & Rutter, 2005). These children with Down syndrome and identified autistic tendencies or ASD are referred as having a so-called “dual diagnosis”, which means that these two are coexisting conditions. There have also been some survey studies in Europe (UK and Sweden) and in the USA suggesting that about 5–10 % of children with Down syndrome could have been diagnosed with co-morbid ASD (Kent, Evans, Paul, & Sharp, 1999; Rasmussen, Borjesson, Wentz, & Gillberg, 2001). Some of the researchers in the field are worried about a tendency to over-diagnose ASD in children with Down syndrome, so it is important to say that a vast majority of individuals with Down syndrome show no evidence of ASD (Howlin et al. 1995; Starr et al., 2005).

Prader–Willi syndrome is a rare genetic condition caused by an error in one or more genes. The responsible genes are not yet identified, but research shows that most likely the problem lies in a particular region of chromosome 15 (e.g. missing, doubled from maternal and none from paternal side, or defective paternal chromosome) (Dimitropoulos et al 2013). It presents as a number of physical, intellectual and behavioural problems. A key symptom of Prader–Willi syndrome is the constant sense of hunger (hyperphagia) that usually begins at the age of two and is caused by the dysfunction of the hypothalamus, which controls hunger and thirst. Children with Prader–Willi syndrome often show mild to moderate impairment in intellectual functioning (e.g. thinking, reasoning, problem-solving). Even those without significant ID have some learning disabilities. Infants with Prader–Willi syndrome have poor muscle tone (e.g. hypotonic muscles, poor sucking reflex), lack of eye coordination (strabismus) and poor responsiveness or reaction to various stimuli. During early childhood, the person with Prader–Willi syndrome feels constant hyperphagia and usually has trouble with weight control (Bohm et al. 2015). Children with Prader–Willi syndrome have underdeveloped sex organs (hypogonadism), delayed motor development, speech-language disorder (e.g. delayed language development: dysarthria), sleep disorder, abnormal curvature of spine (scoliosis), endocrine problems (e.g. hypothyroidism, growth hormone deficiency, central adrenal insufficiency) and high pain tolerance that makes it very difficult to identify injury or illness. They also have various social and behavioural problems (e.g. sharp temper, rigidity, repetitive and obsessive-compulsive behaviour, aggressiveness towards themselves and others) (Lo, Siemensma, Collin, & Hokken-Koelega, 2013).

Several studies investigated the co-morbidity of Prader–Willi syndrome with ASD. The study of Descheemaeker, Govers, Vermeulen, and Fryns (2006) investigated 59 individuals with Prader–Willi syndrome and 59 controls with non-specific ID. They were matched for levels of intelligence (IQ), age, and gender. Results of this study showed prominent autistic-like behavioural phenotypes in the majority of individuals with Prader–Willi sy ndrome (Descheemaeker et al., 2006). Results revealed that even if a person with Prader–Willi syndrome had a higher level of intelligence, s/he still developed autistic behavioural tendencies. Descheemaeker et al. suggest reconsidering the classic symptomatology of persons with Prader–Willi syndrome to a broader ASD symptomatology.