Restricted, repetitive patterns of behavior, interests, or sensory experiences<\/strong>.
<\/li>\n<\/ol>\n\n\n\nThe presentation of ASD is highly diverse. Severity, symptom type, and presence of comorbidities vary considerably among individuals, meaning that each child\u2019s developmental path and daily challenges may differ from those of others.<\/p>\n\n\n\n
This diagnostic concept originated in the 1940s with the work of Drs. Leo Kanner and Hans Asperger, each identifying distinctive developmental traits. Today, ASD is understood as a unified continuum\u2014or spectrum\u2014and this integrated view was formally adopted in the DSM\u20115<\/strong> (2013, published by the American Psychiatric Association) and the ICD\u201111<\/strong> (World Health Organization). As a result, diagnoses formerly labeled separately (such as Asperger\u2019s syndrome, Autistic Disorder, and PDD\u2011NOS) are now encompassed under the single term ASD.<\/p>\n\n\n\nASD is believed to involve strong genetic contributions and is among the most heritable neurodevelopmental disorders. Both rare variants (e.g., rare gene mutations) and common variants (genetic polymorphisms), as well as environmental influences during pregnancy and epigenetic mechanisms, appear to play interacting roles.<\/p>\n\n\n\n
Rising rates of ASD diagnosis are observed in recent years, reflecting improved diagnostic techniques and greater societal and medical awareness. However, ASD remains underrecognized and underdiagnosed in many countries and populations. Women, adults, and ethnic minorities\u2014especially\u2014are more likely to be overlooked for diagnosis.<\/p>\n\n\n\n
<\/span>Epidemiology<\/span><\/h2>\n\n\n\nGlobal prevalence of ASD varies depending on region, diagnostic criteria, and healthcare access. A meta-analysis of over 1.2 million individuals estimated a worldwide prevalence of about 0.72%<\/strong>. In high-income countries between 2015 and 2019, the estimate rose to around 1.18%<\/strong>.<\/p>\n\n\n\nA notable male-to-female ratio of approximately 4:1 is seen in most studies, though this varies by subtype\u2014for example, Asperger\u2019s syndrome has been reported at a 9:1 ratio. One explanation is that women often camouflage ASD-related symptoms by imitating others\u2019 behaviors, making diagnosis less likely to occur.<\/p>\n\n\n\n
Reported prevalence in North America is around 1.01%<\/strong>, Europe about 0.73%<\/strong>, Asia about 0.41%<\/strong>, and in Australia it can be as high as 1.7%<\/strong>. Data from Africa remain limited and show substantial variability\u2014largely reflecting disparities in diagnostic systems, medical infrastructure, and research funding.<\/p>\n\n\n\n<\/span>Characteristics of the Disorder<\/span><\/h2>\n\n\n\nASD is classified as a neurodevelopmental disorder<\/strong> and typically first emerges before age three. Diagnosis requires that symptoms interfere with daily life and cannot be explained solely by intellectual disability or global developmental delay.<\/p>\n\n\n\nTwo broad types of ASD are recognized:<\/p>\n\n\n\n
\n- Syndromic ASD<\/strong>: associated with specific genetic conditions (e.g., Fragile X syndrome, Rett syndrome), where genotype\u2013phenotype relationships may be relatively clear, though such cases are less common overall.
<\/li>\n\n\n\n- Idiopathic ASD<\/strong>: where no specific cause is identified.
<\/li>\n<\/ul>\n\n\n\nA hallmark of ASD is its high heterogeneity<\/strong>\u2014individuals with ASD may range from having severe intellectual disability to above-average intelligence, and language ability may range from non-verbal communication to fluent speech.<\/p>\n\n\n\nASD commonly co-occurs with other developmental, psychiatric, neurological, and physical conditions, complicating diagnosis and influencing developmental trajectories.<\/p>\n\n\n\n
<\/span>Implicated Genomic Region<\/span><\/h2>\n\n\n\nASD is genetically complex and highly heritable. Twin and family studies estimate heritability between approximately 52% and 90%<\/strong>.<\/p>\n\n\n\n<\/span>Rare Variants<\/strong><\/span><\/h4>\n\n\n\n\n- De novo mutations<\/strong> (mutations not present in either parent, arising spontaneously) may include point mutations or copy number variations (CNVs), such as deletions or duplications.
<\/li>\n\n\n\n- These are more often seen in individuals with intellectual disability, epilepsy, multiple unaffected siblings, or females.
<\/li>\n\n\n\n - Specific ASD-related genes include SHANK3, NLGN3, NLGN4<\/strong> (synapse-related), CHD8, MECP2, TBR1<\/strong> (chromatin\/transcription regulation), TSC1, TSC2, PTEN<\/strong> (mTOR pathway regulators), FMR1, UBE3A<\/strong> (protein synthesis\/degradation).
<\/li>\n\n\n\n- CNVs in regions like 1q21.1, 15q11\u201313, 16p11.2, and 22q13.3<\/strong> (which includes SHANK3) have also been associated.
<\/li>\n<\/ul>\n\n\n\n<\/span>Common Polygenic Risk<\/strong><\/span><\/h4>\n\n\n\nMost individuals with ASD show evidence of cumulative risk from small-effect variants dispersed across many genes\u2014a polygenic architecture. Genome-wide association studies (GWAS) are elucidating these contributions. While polygenic risk scores (PRS) are being developed for potential diagnostic or predictive use, clinical application remains some way off.<\/p>\n\n\n\n
Family- and twin-based analyses estimate ASD heritability in the 52\u201390% range. Genetic factors are even more evident in individuals with comorbid intellectual disability, epilepsy, or identifiable syndromic features.\u30a7\u30cb\u30c3\u30af\u30ea\u30b9\u30af\u30b9\u30b3\u30a2\uff08polygenic risk scores\uff09\u300d\u3068\u547c\u3070\u308c\u308b\u65b0\u305f\u306a\u6307\u6a19\u3092\u3001\u8a3a\u65ad\u3084\u4e88\u6e2c\u306b\u6d3b\u7528\u3057\u3088\u3046\u3068\u3059\u308b\u8a66\u307f\u3082\u9032\u3081\u3089\u308c\u3066\u3044\u307e\u3059\u304c\u3001\u5b9f\u969b\u306e\u533b\u7642\u73fe\u5834\u3067\u306e\u5fdc\u7528\u306b\u306f\u3001\u306a\u304a\u6642\u9593\u3092\u8981\u3059\u308b\u3068\u898b\u8fbc\u307e\u308c\u3066\u3044\u307e\u3059\u3002<\/p>\n\n\n\n
<\/span>Etiology(Causes)<\/span><\/h2>\n\n\n\nASD does not arise from a single cause; rather, it represents a final common phenotype<\/strong> resulting from multiple developmental disruptions. Contributing factors include:<\/p>\n\n\n\n\n- Genetic factors<\/strong> (rare and common variants)
<\/li>\n\n\n\n- Neurobiological traits<\/strong>
<\/strong><\/li>\n\n\n\n- Environmental influences during prenatal and perinatal periods<\/strong>
<\/strong><\/li>\n\n\n\n- Epigenetic dysregulation<\/strong> (altered gene expression control)
<\/li>\n<\/ul>\n\n\n\nThese factors may converge on early neurodevelopmental mechanisms\u2014including synapse formation, neural circuitry, and signal transduction pathways.\u5408\u4f75\u3059\u308b\u65b9\u3001\u307e\u305f\u75c7\u5019\u6027\u306e\u7279\u5fb4\u304c\u3042\u308b\u65b9\u3067\u306f\u3001\u907a\u4f1d\u7684\u8981\u56e0\u306e\u5bc4\u4e0e\u304c\u3088\u308a\u660e\u78ba\u306b\u793a\u3055\u308c\u308b\u3053\u3068\u304c\u591a\u3044\u3067\u3059\u3002<\/p>\n\n\n\n