Global Data on Autism Spectrum Disorders Prevalence: a Review of Facts, Fallacies and Limitations

Universal Journal of Clinical Medicine 5(2): 14-23, 2017 http://www.hrpub.org DOI: 10.13189/ujcm.2017.050202

Global Data on Autism Spectrum Disorders Prevalence: A Review of Facts, Fallacies and Limitations

Onaolapo A Y1, Onaolapo O J2,*

1Behavioural Neuroscience/Neurobiology Unit, Department of Anatomy, Ladoke Akintola University of Technology, Ogbomoso, Oyo State, Nigeria 2Behavioural Neuroscience/Neuropharmacology Unit, Department of Pharmacology, Ladoke Akintola University of Technology, Osogbo, Osun State, Nigeria

Abstract Autism spectrum disorders (ASDs) are a in the early to mid-1960s [2, 3], while the first range of neurodevelopmental disorders whose aetiologies hospital-based survey in sub-Saharan Africa was are largely unknown. In the past few decades, studies have conducted in five countries in the late 1970s [4]. Autism demonstrated that ASDs occur globally, and that the surveys have since become global, with different countries numbers of recorded cases are rising; however, conducting surveys to determine the prevalence and risk determining the true prevalence figures is still a major factors in their communities [1, 5], and thereby propose challenge, especially in developing nations. Also, subtle strategies to improve identification, diagnosis, differences in cultural norms might impede timely/accurate management as well as promote policy reforms that bring diagnosis and categorisation of patients. In this review, we awareness to the plight of the autistic child. examine the globally-available data on the prevalence of The term ‘Autism’ derives from the Greek word "autos", ASD and discuss some of the challenges of data acquisition, meaning "self”; and it was in the year 1911 that Eugen with reference to how these may impact the reliability of Bleuler first used the word autism in describing a symptom figures obtained. Some of the facts, fallacies and of schizophrenia. However, in 1943 and 1944 respectively, limitations relating to the presently-available figures are Leo Kanner (USA) and Hans Asperger (Germany) also highlighted. described individuals with social/emotional limitations and withdrawn behaviours. Kanner reported behavioural Keywords Neurodevelopment, Aetiology, Prevalence, aberrations such as poor social interaction, obsessiveness, Autism, Data stereotypic movement, and echolalia in the affected children. It was Kanner who first coined the term ‘infantile autism’ (earlier called Kanner’s syndrome) to describe his observations in this group of children who seemed 1. Introduction socially-isolated and withdrawn [6]; while Asperger named the condition he observed Asperger’s syndrome. Decades Epidemiology is not only concerned with patterns of of research will eventually reveal that both syndromes are disease occurrence within human populations, but it is also parts of a highly-variable spectrum of disorders. Autism concerned with the factors that determine or influence spectrum disorders (ASDs) are an array of development of disease, or maintenance of health. Over the neurodevelopmental disorders characterised by cognitive years, different study designs (surveillance, descriptive, and neurobehavioural deficits, whose underlying factors analytical, cohort, case-control and cross-sectional) have are genetic and/or neurobiological [7]. In the Diagnostic been employed in examining the relationships that may and Statistical Manual (DSM) III, autism debuted in 1980 exist between disease and disease determinants in defined as "infantile autism", which was replaced by the term human populations. Generally, epidemiological "Autistic Disorder" in 1987. In the DSM IV, it was referred investigations of neuropsychiatric diseases begin with to as pervasive developmental disorders (PDDs); and cross-sectional surveys, which help to determine the consisted of autistic disorder (autism), Asperger disorder, prevalence of the disease condition, patterns of risk factors, childhood disintegrative disorder, Rett syndrome, and as well as the possible correlates between disease and risk PDD-not otherwise specified (NOS). factors among representative samples [1]. The first Over the years, a lot has changed about our perception of epidemiological survey of autism was initiated in England ASDs, the perceived risk factors, core diagnostic criteria, Universal Journal of Clinical Medicine 5(2): 14-23, 2017 15

and even approaches to management. Presently, according the human brain (notably the cerebellum and cingulate to the DSM V, persistent deficits in social communication/ gyrus) in autistic children) [15]. social interaction and a restricted/repetitive (stereotypical) The cause(s) of the above-mentioned pathological patterns of behaviour, interests or activities; which must be changes are traceable to both genetics and the environment. present in the early developmental period(but might not The heterogeneity of ASD is not only reflected in its become obvious until social demands exceed limited behavioural manifestations, but also in the genetic basis, as capacity), cause clinically significant impairment (in social, many candidate ASD genes have been studied or occupational or other important areas of current implicated [16]. Also, while studies may differ in terms of functioning) and must not be better explained by their conclusions regarding the degree of involvement of intellectual disability or global developmental delay, are genetics, it is generally accepted that genetics plays a the core criteria for the diagnosis of ASD [8]. DSM 5 also crucial role in ASD. Presently, candidate genes that have makes provision for differential diagnosis such as ‘social been implicated in ASD include those that encode for communication disorder’. Level of severity of symptoms neural adhesion molecules, ion channels, scaffold proteins, {3 levels given for both social communication/social protein kinases, receptor/carrier proteins, signaling interaction, and restricted/repetitive (stereotypical) patterns modulator molecules, and circadian relevant proteins [17]. of behaviour} determines the degree of supportive care Environmental factors that had been linked to needed, with level 3 severity requiring very substantial ASD-associated neuroinflammation and immune support. Apart from the core symptoms, patients often have dysfunction include early-life exposure to various co-morbid psychiatric and behavioural manifestations like xenobiotics including heavy metals such as lead, mercury self-injury, aggression, impulsivity, hyperactivity, anxiety and aluminium [18]. The Ethyl mercury compound and mood symptoms; all of which may worsen the overall (Thimerosal) is a bacteriostatic agent that was a component prognosis, stress the caregivers, and further complicate of a number of childhood vaccines in Western nations. The management. Recently, results from epidemiological possibility of its involvement in ASD led to its removal surveys indicate that the global prevalence of ASDs is on from many vaccines meant for children; and while it must the rise; although data from sub-Saharan Africa and a be noted that this was not accompanied by a sharp decline number of other developing countries still show numbers in ASD prevalence, its continued use in vaccines given to that are generally lower than those from the developed pregnant women further complicates the picture [18]. The countries [9-11]. Whether this reflects an absolute low use of aluminium(Al) as an adjuvant in many vaccines has prevalence, deficits in diagnostic skills, mal-adaptation of continued, due to the fact that Al salts help to stimulate the diagnostic criteria as it relates to cultural differences in immune system to yield adequate antibody titres [19]. behaviour, or under-sampling is still being studied. However, there is abundant scientific literature on the The aetiology of ASD is still being studied, and despite neurotoxic effects of Al; and its ability to adversely affect years of research, a complete understanding of the both the immune and the nervous systems, hence making it causative factors is still elusive; and while it is now known a plausible risk factor for triggering ASD [18]. Al’s ability that genetics may plays a big role in ASD, a rapidly to alter neuronal gene expression can also affect the increasing prevalence suggests a bigger role of response of neurons to environmental insults such as toxins environmental factors. [18]. The presence and abundance of environmental risk Generally, abnormalities in neural connectivity factors may be a major determinant of geographical involving synapses, tracts and neuronal communication via variations in the true prevalence figures of ASD; however, neurotransmitters are key pathological features of the brain the wide variety of candidate environmental risk factors in autism [12]. Neurodevelopmental defects in synapse makes matching environmental factors to prevalence a formation/elimination and changes in ratios of challenging task. inhibitory/excitatory synapses leads to defective local and There have also been reports suggesting that some of the long range connectivity [12]. An active neuroinflammatory behavioural characteristics of “autistic” children in process involving the cerebral cortex and the cerebellum; developing countries differ, when compared to those in with associated loss of cerebellar Purkinje cells, marked developed nations [20, 21]. Along this line, how reactivity of the Bergmann’s astroglia in areas of Purkinje prevalence figures are influenced by the beliefs and cell loss, marked astroglial reactions in the granule cell cultural heritages of the different regions of the world is a layer and cerebellar white matter, and astroglial reactions matter of debate. In this review, we discuss the global in the middle frontal/cingulate gyri had been demonstrated epidemiology of ASDs by highlighting the incontrovertible by neuropathological examinations [13]. This facts relating to its prevalence, fallacies of neuroinflammation may have a strong link to misinterpretation of available figures as they are, and autoimmunity, based on demonstrable elevated levels of limitations of data acquisition, diagnosis and categorisation immunoglobulins (IgG, IgM and IgA) against select of patients. We also summarise how these factors impact neuron-specific antigens in ASD children [14]; and a strategies to improve identification, diagnosis and significantly higher presence of serum auto-antibodies to management; as well as promote policy reforms. 16 Global Data on Autism Spectrum Disorders Prevalence: A Review of Facts, Fallacies and Limitations

1.1. Global Prevalence of ASDs the Study of Autism in Canada (NEDSAC) ranks ASD as one of the most common developmental disabilities, 1.1.1. Prevalence in USA, Europe, China, Japan, Middle affecting 1 in 94 children [38]. A pilot study that was East, Ecuador, Brazil and Mexico conducted in Brazil reported a prevalence rate of 27/10,000 Global data on the prevalence of disorders that now fall [39]; while the prevalence of ASD in regular under the term ASDs had been available before 2013. In a schoolchildren in Quito, Ecuador was found to be 2012 review that compared prevalence data from different 11/10,000 persons [40]. The Leon survey in Mexico parts of the world (excluding sub-Saharan Africa), the reported an overall prevalence of 87/10, 000; a rate that researchers estimated the median global prevalence of was deemed consistent with other studies conducted at a 17/10,000 (approx. 1 in 588) for autistic disorder, and similar period [41]. 62/10,000 (approx. 1 in 161) for all pervasive developmental disorders; while suggesting that the 1.1.2. Prevalence of Autism in Sub-Saharan Africa, India increase in estimates over time and the variability between and the Caribbean Islands countries and regions may be linked to diagnostic oAccording t the World Health Organisation, the global switching, the broadening diagnostic criteria, service prevalence of ASD has been estimated as 1 per 160 persons availability and the increasing global autism awareness [42]. However, the contribution of sub-Saharan Africa [22]. Even prior to this, the epidemiology of ASDs had (SSA) to this burden is largely unknown due to a paucity of portrayed a shifting dynamics, with prevalence increasing population-based surveys on autism in this region [10, 11, from 2-4/10,000 children as reported in the 1940s [23], to 22, 42, 43]. Data (largely from hospital-based studies) are approximately 4-5/10,000 children, according to the however available from a few countries in the region. In studies that were published in the 1960s and 1970s [24, 25], south-west Nigeria, Lagunju et al [44] reported a 11/1000 children in the USA, according to a survey prevalence rate of 2.3% (1 in 43.5) amongst 2,320 conducted about a decade ago [26]; while a Centres for first-time attendees of a neurology or child psychiatry Disease Control and Prevention surveillance report clinic. In another clinic-based study in south-eastern revealed a combined estimated prevalence of 14.6 per Nigeria, prevalence of ASD was reported to be 0.8% (1 in 1,000, or 1 in 68 children (aged 8 years, whose parents or 125) of the total number of children attending the clinic for guardians resided in 11 ADDM Network sites) in the that year [45]; while in Uganda, a survey of 1,169 children United States [27]. The most recent CDC figures on ASD aged between 2 and 9 years reported an unadjusted published in 2015 (which are believed to be more accurate) prevalence for ASD of 6.8/1000 [46]. All studies reported a say 1 in 45 children in the USA have ASD; this is however male predilection, and middle to high socioeconomic status based on a parent survey which was designed to track the improved the likelihood of a child being evaluated for ASD. prevalence of developmental disorders in children aged 3 While these studies provided some data, the absence of to 17 years [28]. Studies in Europe recorded before 1999 data from large scale epidemiological studies from a reported prevalence rates ranging from 1.9 to 72.6 per number of countries in this region have been suggested as a 10,000 with a median of 18.75/10,000; while studies possible reason for the perceived low incidence and/or conducted after 1999 reported rates ranging from 30.0/10 prevalence of autism observed in SSA [10, 11]. 000 to 116.1/10 000, with a median rate of 61.9/10 000 [22]. Until recently, India (like SSA) had a paucity of In the United Kingdom, a 2006 study in 9-10 year-olds community-based population studies for autism; although reported a prevalence of childhood autism as 38.9/10,000, there was a number of hospital-based autism clinical while other ASDs (DSM III) was 77.2/10,000 (52.1-102.3), assessment studies [47-49]. However, in a 2017 making the total prevalence of all ASDs 116.1/10,000 [29]. population-based study (of 28, 078 children aged between However, in 2014, the National Autistic Society reported 1 and 10 years, cutting across geographical regions that that 1 out of every 100 children has ASD [30]. In China, it represent rural, urban, and tribal populations in India) using was estimated that 1.1 in every 1,000 children are the Hindi version of the Indian Scale for Assessment of diagnosed with autism [31]; while in an analysis of five Autism; a prevalence of 0.15% (1 in 667) was reported, studies from mainland China, an estimated pooled mean with a male sex predilection [50]. Also, a high prevalence of 24.4 per 10,000 children was observed [32]. socioeconomic status increased the likelihood of an ASD In a2 201 review of epidemiological studies conducted in diagnosis [50]. The prevalence of ASD in the study was the Western Pacific region (including Japan and China) observed to be higher amongst children aged between 4 since 2000, Elsabbagh et al. [22] reported that prevalence and 10 years with majority of them diagnosed with mild rates varied from 2.8/10 000 to 94/10 000 with a median autism; while amongst children aged between 1 and 7 years, value of 11.6/10 000. In the Middle East, the prevalence of the diagnosis of moderate autism was prevalent. This was ASD was reported to be 1.4/10,000 in Oman, 29/10,000 in however attributed to families delaying presentations till the United Arab Emirates, and 4.3/10,000 in Bahrain the onset of delayed motor and speech development [50]. [33-37]. In an earlier study, the same authors (sampling 11,000 In Canada, the National Epidemiological Database for children within the same age range, and from the same Universal Journal of Clinical Medicine 5(2): 14-23, 2017 17

region) reported a prevalence of 0.0009 % (1 in 1100), with underreporting stemmed from studies conducted amongst low socioeconomic status correlating positively with children born to African immigrants in Sweden [53-55], autism [51]. that reported high prevalence rates in this subset of the In the Caribbean islands, the Aruba Autism Project population, compared to the indigenous population. The determined the prevalence of ASDs in birth years possibility of late diagnosis or misdiagnosis has also been 1990–1999 in Aruba, and found a figure of 53/10,000 [52]. considered, and studies have shown that African children are more likely (than Caucasian children) to have a late diagnosis of ASD [56], or a misdiagnosis [57]. 2. Autism Spectrum Disorders: The Despite the lower figures (when compared to developed Facts and Fallacies nations), it is safe to say that even in SSA, the prevalence rates of ASDs are on the rise; and there has been an Autism fact sheets from different advocacy groups ‘improvement’ from an era of no prevalence figures [22] to (Autism Society, National Autism Association, National the availability of hospital-based [44], or Autism Network, Talk About Curing Autism, National community–based [46] prevalence figures. Also, in India, Autism Network, Autism South Africa, Action In Autism, the prevalence from a 2017 study [38] revealed a rise from Autism Speaks etc.) irrespective of region or country an earlier 2015 study [51]. generally accept and reiterate that autism is a In developed nations, a number of researchers have bio-neurological developmental disability which generally attributed the rise in ASD prevalence to an increasing appears before the age of 3; impacting normal brain ability to diagnose, or a possible reflection of the success of development in the areas of social interaction, public health systems in better-identifying children who communication skills, and cognitive function. There have were previously undiagnosed [58]; and this is also related also been suggestions that autism is a disease of developed to the continued redefinition of diagnostic criteria [22]. An countries, with a male sex predilection, that does not affect increased awareness is also thought to be largely life expectancy. While currently, there is yet no cure for responsible for changing figures in less developed regions autism, early diagnosis and treatment helps to improve the of the world, such as SSA [10, 11], and Asia [50, 51]. diverse symptoms associated with autism. Comparing the two Indian studies cited earlier [50, 51], it is obvious that more children were recruited in the 2017 study 2.1. ASDs Occur Globally than were in the 2015; suggesting that in the 2 year period, more families were aware enough to want to seek diagnosis In relation to the prevalence of ASDs, data emanating and treatment for their wards. There is also evidence of from developed nations appear more comprehensive and increasing awareness, cultural reorientation and the reliable, compared to those from developing nations. availability of well-trained child and adolescent care Despite this, one fact that can no longer be denied is that as specialists and allied professionals in SSA. In the last it stands today, ASDs occur globally irrespective of culture, decade, particularly in the last 5 years, the number of ASD geography or degree of industrialisation; with variable related studies in this region [44, 46, 59-61] has increased degrees of tangible data from different regions of the world considerably, compared to the preceding decades. where studies had been conducted. Hence, contrary to what A review of a recent CDC data published in the National might have been believed in the past, especially in the Health Statistics Reports [28] also supports the theory that developing countries, it is not a disorder of ‘the West’ or of changes in awareness, earlier diagnosis, and redefinition of advanced nations. The realisation of this fact is of diagnostic criteria has a lot of impact on prevalence figures. particular importance in SSA and other regions of the While the autism rate appeared to rise 79 % over a 3-year world where awareness levels are still growing. period, the rate of developmental delay dropped 36 % [28]; and the combined prevalence of children diagnosed with 2.2SD. A Prevalence Figures are Still Rising autism, developmental delay and intellectual disability did not change over the 3 years. The unchanging statistic of the Globally, the recorded prevalence figures for ASDs are sum data suggests that a number of children who were once rising; and from a statistical point of view, this is tagged as having developmental delay or intellectual undeniable when we examine data from both developed disability are now being identified as having autism [28]. and developing countries. However, in many developing In a study involving Danish children, Hansen and countries, the reported rates continue to be significantly colleagues [62] were also of the opinion that the increase in lower than the developed countries [9]. Whether this truly prevalence of ASD was actually due to changes in how the reflects an absolute low prevalence, deficits in diagnostic disease is diagnosed [62]. By using data from a large study skills, mal-adaptation of diagnostic criteria as it relates to involving 677, 915 Danish children (born between 1980 cultural differences in behaviour, or under sampling are and 1991) and tracked until they either had an autism issues that continue to be discussed. The idea that the low diagnosis or reached the terminal date of the study (Dec. 31, prevalence rates observed in SSA could be due to 2011); the authors concluded that significantly more 18 Global Data on Autism Spectrum Disorders Prevalence: A Review of Facts, Fallacies and Limitations

children were diagnosed with autism in 1995 and thereafter, improved ability to diagnosis b) The public response that than before 1994 (when autism became a spectrum of followed the Wakefield article attests to the societal and disorders in Denmark) [62]. However, the authors also social burden of ASDs, and the dangers of the inability of noted what appears to be a certain degree of real increase in science to find a sound and timely answer in relation to the prevalence. cause(s) of a disorder that continues to plague more Several researchers also share the opinion that there is a children. It is therefore imperative to continue to research real global rise in prevalence of ASDs, and the rise may be and identify environmental and social factors that may the product of several factors such as exposure to increase risk of ASDs. environmental toxins and increasing parental age/genetic susceptibility [63-65]. Immune dysregulation in pregnancy SD2.3. A has a Male Sex Predilection has also been linked to the rising prevalence of ASD; and autoimmune inflammatory disorders, such as coeliac Sexual predilections in disease prevalence are disease and rheumatoid arthritis in mothers are believed to well-recognised, and female predilections have been increase the risk [66]. Inflammation due to common reported consistently in a number of disorders with infections and endemic parasitic illnesses are probably not autoimmune aetiologies [70] while a male preponderance likely associated with increased risk; and this is consistent has been observed in some neurodevelopmental disorders with the observation that in some developing nations such [71-73] ASDs have also been observed to have a higher as Nigeria or Cambodia, where parasitic and infectious prevalence in males, compared to age-matched females; in diseases are still common, recorded ASD prevalence is still a 4:1 ratio. This observation has been consistent across low [45, 67]. populations, regions and time; strongly suggesting the The continued increase in prevalence figures of ASDs in involvement of sex-specific biological factors in ASD developed countries led to the postulation of the “Biome aetiology [74, 75]. Genetic studies have demonstrated that Depletion Theory” by some researchers, who believe that females are protected from the effects of de novo and maternal immune response overreaction is a factor heritable ASD risk variants, with suggestions that sex underlying the development of ASDs in offsprings. hormones or sex chromosomal genes may modulate these According to this theory, our immune system has genetic variations [74], for a detailed review on the co-evolved alongside microbes and parasites, but a lack of influence of sex in autism (see Halladay et al., [75]). these pathogens in urban, post-industrial societies leads to immune system over reactivity [67]. Along this line, it was 2.4. ASD and Life-expectancy suggested that pro-biotics may be able to control the inflammatory response in pregnant women, and prevent Its i generally believed that autism per se does not affect some cases of ASD; however, this notion still seems like a life expectancy; however, research continues to show shot in the dark, and studies will have to be conducted to higher mortality risk among individuals with ASD. In examine this. comparison with mortality statistics from the general The apparent induced immune system over-reactivity population or general population controls, the risk of also formed the basis of an implied link between premature mortality has been estimated to be 2-fold to vaccination and ASDs. In 1998, a case series published by 10-fold higher in the ASD population; even autistic adults Wakefield and colleagues, but later retracted by 10 of the without a learning disability are 9 times more likely than 12 authors suggested that the measles, mumps, and rubella controls, to die by suicide [76]. Also, risk of mortality is (MMR) vaccine could predispose to behavioural symptoms higher in females, compared to males [77]. Accidents such that are representative of ASDs in children. Despite certain as drowning and co-morbid medical conditions such as obvious shortcomings of this study {including the very epilepsy are among the classic causes of death; however, small sample size (n=12)}; the publication generated a these cannot fully account for the life span gap between social firestorm that led to some parents rejecting autistic and non-autistic people, or the difference in vaccination for their children. However, epidemiological mortality between autistic people with and without an studies conducted thereafter failed to establish such a link intellectual disability [76]. One of the factors that could [68, 69]. The CDC also continues to reiterate its position account for this gap is an increase in the prevalence of that no such links exist. Again, a number of developing health problems such as diabetes and respiratory disease; countries who have contributed to the global data on ASD and the fact that these health problems may go unnoticed prevalence do not have immunisation regimens like MMR; until it is too late [76]. Among autistic adults, pressures of and even if they do, data establishing a link appear meeting the obligations of ‘normal life’ may lead to non-existent. From the foregoing, the following are continued isolation, depression and suicide. The apparent: a) an undeniable deduction from the study by relationship between ASD and life-expectancy deserves Hansen et al [62]is that is not all new cases of ASDs are further studies, especially, with the realisation that certain explicable by changes in diagnostic ability; hence, it might life-threatening medical conditions are more common in be unscientific and over simplistic to attribute all to ASD patients. Therefore, it might be erroneous to simply Universal Journal of Clinical Medicine 5(2): 14-23, 2017 19

state that ASD does not affect life-expectancy without the true figures are likely to be gotten from the community, explaining the ever-increasing complexity of the and the present figures should be treated with caution until relationship. larger community-based studies are carried out. However, while the value of an epidemiological study for assessment of needs and priorities within a community cannot be over- 3. ASD Global Epidemiology: emphasised; the cost implication of such studies may be Limitations of Acquisition, high, with a number of developing countries not finding them easily-affordable, especially in the face of pressures Interpretation and Viability of Data from other competing priorities. An accurate global comparison of data relating to the prevalence of ASDs is a rather challenging task, due to 3.2. Impact of Culture factors such as; a) the absence of data from large scale epidemiological studies from a number of countries, Cultural differences play a large role in disease diagnosis, especially in the sub-Saharan countries like Nigeria (where especially when considering the diagnosis of disorders that most of the available rates emanated from hospital-based tends to attract a lot of social stigma; therefore, despite studies); even, developed nations like the USA cannot adequate sensitisation and awareness, parents may still boast of a truly all-inclusive national survey, probably due refuse to submit their children for ASD evaluation. For to impediments of cost effectiveness and logistics b) the instance, in South Korea, a risk of intense stigmatisation information gathering tools are not totally adaptable to or makes many families of children with developmental may not yield 100 % accuracy in some regions of the world delays to intentionally avoid diagnosis of ASD; also because of certain cultural peculiarities that might affect cultures that believe that speech development in the male diagnosis or categorisation c) there could be wide regional child is usually slower than females make seeking early variations in figures arising from the same country, as is the help for the child to be impossible [9]. Therefore, societal case with China [32]. or parental behaviours affect ASD prevalence figures. The lack of a culturally-adaptable tool for ASD screening constitutes another impediment to having 3.1. Absence of Population-based Prevalence Data in reliable prevalence data; since culture/language differences Developing Countries might affect diagnosis rates. Different cultures have The prevalence figures of ASD in sub-Saharan Africa peculiar behaviours that are at least acceptable, if not even have been based mainly on a few hospital-based studies, desirable. Diagnosis of ASD is not based on laboratory and hardly any community-based study, except that of tests, but rather, on the exhibition of certain behaviours. Kakooza-Mwesige et al [46] in Uganda. Under these These behaviours include the tendency to establish eye circumstances, under-sampling or ‘skewed’ sampling have contact, ability to form relationships with others, been suggested to negatively impact the reported milestones in language development, and the presence of prevalence [10, 11]. The study by Lagunju et al [44] was certain repetitive motor and play behaviours. Cultural conducted in a tertiary hospital setting in south-west perceptions affect the exhibition of at least some of these Nigeria, while that of Bakare et al [45] was conducted in a behaviours; and in different cultures, parental perceptions similar setting in south-eastern Nigeria. These centres are of their presence or otherwise affect the timing of seeking the ultimate referral centres for paediatric patients in their help for a child with possible ASD. Therefore, behaviours respective regions and they represent a ‘gathering point’ that are considered normal in some cultures may fall within for all ‘puzzling’ and ‘unusual’ childhood illnesses. First, it the inclusion criteria for ASD diagnosis. must be noted that there are other regions (in the country), Generally,n i Europe and America, children are expected for which there are no data. Secondly, confidently drawing and encouraged to make eye contact with others; but in an inference from such studies is associated with two other parts of the world such as Asia and Africa, or even potential pitfalls; that of under-representation, due to an among native communities in America and Europe, this is apparent small sample size, compared to the total not encouraged, and may even be perceived as rudeness or population of children within the age range; or of insubordination, especially, when interacting with adults. over-representation, because the sampling frame is This has made certain researchers to be of the opinion that compelled to fall on an area where such cases are likely to the matter of use of eye contact as a diagnostic criterion for cluster. This clustering effect may the apparent from the autism needs to be handled with caution. There are also figures; in Nigeria, Lagunju et al [44] sampled from the cultural variations in the degree of a child’s interaction paediatric neurology clinic and got a prevalence of 23/1000 with others, especially with adults. There are cultures all and Bakare et al [45] sampled from a general paediatric over the world (Africa, Asia, Central and South America) clinic to return a figure of 8/1000; while in Uganda, that don’t encourage ‘undue’ interactions between children Kakooza-Mwesige et al [46] sampled from the community and adults (especially strangers). How children in these and got an unadjusted figure of 6.8/1000. It is obvious that cultures form relationships may not be exactly what is 20 Global Data on Autism Spectrum Disorders Prevalence: A Review of Facts, Fallacies and Limitations taken to be normal in urban Europe or America; and ASD Conflict of Interest diagnosis in these communities may face an uphill task when the children encounter these ‘strangers’(healthcare Onaolapo AY declares that she has no conflict of interest. personnel) that are questioning, examining and observing Onaolapo OJ also declares that he has no conflict of them. Along this line also, language development may be interest. difficult to assess with all certainty, as the child may simply be scared or ‘ashamed’ to talk to an unfamiliar adult; leading to a situation where the parents vouch that the child Acknowledgements could speak, but he/she will refuse to communicate during the assessment. 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