Causes Autism

it has long been presumed there common cause @ genetic, cognitive, , neural levels autism s characteristic triad of symptoms. however, there increasing suspicion autism instead complex disorder core aspects have distinct causes co-occur.

deletion (1), duplication (2) , inversion (3) chromosome abnormalities have been implicated in autism.

autism has strong genetic basis, although genetics of autism complex , unclear whether asd explained more rare mutations major effects, or rare multigene interactions of common genetic variants. complexity arises due interactions among multiple genes, environment, , epigenetic factors not change dna sequencing heritable , influence gene expression. many genes have been associated autism through sequencing genomes of affected individuals , parents.

studies of twins suggest heritability 0.7 autism , high 0.9 asd, , siblings of autism 25 times more autistic general population. however, of mutations increase autism risk have not been identified. typically, autism cannot traced mendelian (single-gene) mutation or single chromosome abnormality, , none of genetic syndromes associated asds have been shown selectively cause asd. numerous candidate genes have been located, small effects attributable particular gene. loci individually explain less 1% of cases of autism. large number of autistic individuals unaffected family members may result spontaneous structural variation — such deletions, duplications or inversions in genetic material during meiosis. hence, substantial fraction of autism cases may traceable genetic causes highly heritable not inherited: is, mutation causes autism not present in parental genome.

several lines of evidence point synaptic dysfunction cause of autism. rare mutations may lead autism disrupting synaptic pathways, such involved cell adhesion. gene replacement studies in mice suggest autistic symptoms closely related later developmental steps depend on activity in synapses , on activity-dependent changes. known teratogens (agents cause birth defects) related risk of autism appear act during first 8 weeks conception, , though not exclude possibility autism can initiated or affected later, there strong evidence autism arises in development.

exposure air pollution during pregnancy, heavy metals , particulates, may increase risk of autism. environmental factors have been claimed without evidence contribute or exacerbate autism include foods, infectious diseases, solvents, pcbs, phthalates , phenols used in plastic products, pesticides, brominated flame retardants, alcohol, smoking, illicit drugs, vaccines, , prenatal stress. such mmr vaccine have been disproven.

parents may first become aware of autistic symptoms in child around time of routine vaccination. has led unsupported theories blaming vaccine overload , vaccine preservative, or mmr vaccine causing autism. latter theory supported litigation-funded study has since been shown have been elaborate fraud . although these theories lack convincing scientific evidence , biologically implausible, parental concern potential vaccine link autism has led lower rates of childhood immunizations, outbreaks of controlled childhood diseases in countries, , preventable deaths of several children.