History and exam
Key diagnostic factors
common
language delay or regression
Language delay and regression occurs in some children with ASD.
During the first year, parents notice that their children may have delayed language development (lack of vocalization/babble).
Children may not acquire first words at the expected age, or fail to gain words or vocalizations. They may then lose these language skills (regression).[4] They may echo words frequently but, in contrast to typically developing children at this age, do not use spontaneous language of their own.
As older children, they may use phrases they have heard others use in their daily language to a greater degree than typically developing children (stereotyped speech).
By contrast, some children may develop language at a very early age and have relatively "adult like" speech.
verbal and nonverbal communication impairment
Present in all children with ASD to some degree.
Necessary for diagnosis.[2]
There may be reduced protodeclarative pointing (use of the index finger to indicate an object of interest to another person), or reduced pointing integrated with looking at the object and back to the person.
Children frequently don't interact with their parents in a to-and-fro way during the first year, and don't play social games (e.g., peek-a-boo).
Interpreting children's mood may be very difficult as their nonverbal communication methods (facial expression, demeanor, gesture) might not show how they feel; mood may therefore be perceived to change quickly.
Older children and adults (particularly females) may develop adaptive mechanisms to manage situations requiring social communication (e.g., learning social "rules" by imitating their peers). This may mask their symptoms on assessment.[109]
social impairment
Present in all children with ASD to some degree.
Necessary for diagnosis.[1][2]
Children frequently play alone and may be relatively uninterested in being with other children.
Other children may be socially motivated but their approaches may be less sophisticated than other children: for example, being one-sided or in some way inappropriate.
As children get older their difficulties in interactions with other children may lead to lack of friendships or very brief friendships that end due to misunderstandings.
As adults, some individuals with ASD become increasingly socially isolated, but others go on to have relationships and families, and jobs. In general, females with ASD may have more of a desire for friendships and peer group acceptance than males.[109] Adults with ASD (and especially women) may develop adaptive mechanisms to manage social situations, which may mask their symptoms on assessment.[105]
repetitive, rigid, or stereotyped interests, behavior, or activities
Present in all children with ASD to some degree.
Necessary for diagnosis.[1][129]
In children, language may be repetitive, or repetitive requests may be made for parents to say or do something in a particular way (verbal rituals).
Children are noted to have particular ways of going about everyday activities.
May prefer toys and other possessions to be in a certain place.
A need for routine and predictability in their daily activities.
Typically become more distressed than expected if the home environment changes.
Sensory interests or sensitivities and motor mannerisms are common.
Many people with ASD have intense and highly-focused interests, the pursuit of which may be beneficial (and necessary) to their wellbeing. Examples include trains, car registration numbers, or zip codes. Male and female interests overlap, but in general, females may be more likely to be interested in more socially typical domains than males, such as art or music.[110] Compared with normal interests pursued in an obsessional manner, special interests in ASD are intense and all-consuming; they may be pursued to the detriment of other activities (including self-care/daily living activities).
Other diagnostic factors
common
placid or very irritable as a baby
Babies who later go on to be diagnosed with ASD frequently are very quiet and placid, or very upset, irritable, and difficult to put down.
Some parents describe how children are distressed if not being carried around.
feeding difficulties
Children may be very difficult to feed, refuse bottles, and be difficult to wean onto solids.
Children may be distressed by the taste of food, or the sensation of a spoon in their mouths or food around their lips. Sensitivity to certain types of foods or food textures, or the way food is arranged on a plate, may continue throughout life.
unusual posturing
May develop unusual transient stiff postures with their hands or whole bodies.
motor stereotypies
Hand flapping, finger flicking, or whole body mannerisms, for example rocking, spinning around, bouncing up and down, running repetitively back and forth.
sensory interests or difficulties
Evidence of the following sensory interests: visual (looking at lights, from corner of eye at objects, examining objects more closely than expected); tactile (touching or stroking objects or people); olfactory (smelling objects, or familiar or unfamiliar people); gustatory (licking or tasting objects or people). In contrast, there may be sensory-related difficulties, such as a negative and sometimes idiosyncratic reaction to certain textures, sounds, and other sensory stimuli.[13]
uncommon
evidence of other neurodevelopmental disorder
Signs of fragile X syndrome, tuberous sclerosis, dysmorphism (may indicate chromosomal disorder) are weakly associated with ASD.[130]
macrocephaly
Some children with ASD have large heads; a comparison with both parents' head circumferences should be made where possible.[131]
Risk factors
strong
male sex
Boys are more frequently affected than girls (4:1).[10][19] However, the extent to which this difference in reported prevalence is due to relative under-diagnosis in girls and women is unclear. ASD in girls and women is consistently under-reported relative to males.[72][73] This is potentially related to differences in presentation and levels of impairment.[74] Additionally, screening and diagnostic instruments may be less accurate at identifying the characteristics of ASD in females.[74]
positive family history
A study of same-sex twins found 60% concordance for ASD in monozygotic (MZ) twins versus 0% concordance in dizygotic (DZ) twins.[75]
Another twin study found that in MZ twins discordant for ASD, 76% of pairs were concordant for social and cognitive abnormalities related to ASD, suggesting a genetic basis for milder phenotypic variants.[76]
A number of studies estimate the heritability to be between 50% and 80%.[40][41][42][43][44]
The evidence from ASD family studies implied a strong genetic liability to ASD; the chance that a sibling will develop any type of pervasive developmental disorders is 20%.[45][46]
However, despite studies on heritability, it is important to recognize that most children with ASD do not have a relative with ASD.
gestational valproate exposure
Studies report a strong increased likelihood of ASD in the children of mothers who take sodium valproate during pregnancy.[59][60][61] The association appears to be dose-related, and remains robust after adjustment for confounders (e.g., extent of seizures during pregnancy). Valproate is associated with poorer neurodevelopmental outcomes during pregnancy, compared with other antiepileptic drugs, and is now typically contraindicated in pregnancy.[77]
weak
karyotype (chromosomal) abnormalities
Various chromosomal abnormalities have been associated with ASD. Some common abnormalities are listed below.
The most common of these syndromes in children with ASD are inversions/duplications of chromosome 15q11-15.[78]
People with tuberous sclerosis have around a 30% to 50% chance of also having ASD.[79][80]
About 25% of people with neurofibromatosis type 1 have ASD.[81]
About 10% of people with Down syndrome have ASD.[82]
About 30% of people with Fragile X syndrome have ASD.[83]
Rett syndrome has also been associated with ASD.[84]
increasing parental age
Increasing parental age appears to contribute to the development of ASD on both a genetic and nongenetic basis. Maternal and paternal age both independently increase the likelihood of ASD, with an estimated 18% increase (for mothers) and 21% increase (for fathers) for each 10-year increase in parental age.[61]
prematurity
Preterm birth (even up to 37 weeks) is associated with an increased likelihood of ASD, although the effect is greatest in extremely preterm infants.[61][85][86] The brain of a preterm infant is more vulnerable to gray and white matter brain injury affecting subcortical and cortical connectivity, although preterm birth is associated with an increased likelihood of ASD, even without overt neuronal damage.[62] Prematurity-related complications such as anoxia are also likely to be a factor in the development of ASD in some preterm infants.
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