| The causes and etiology of autism are areas | | | | this and its effects are still unknown. |
| of debate and controversy; there is currently | | | | |
| no consensus, and researchers are studying a | | | | Research has not yet established exactly what |
| wide range of possible genetic and | | | | is specific to autism and what may be seen in |
| environmental causes. Since the way autism | | | | other disorders however. |
| manifests is different for each person, there | | | | |
| are likely multiple "causes" that interact | | | | Individuals with autism are also far more |
| with each other in subtle and complex ways, | | | | likely to develop epilepsy than would |
| and thus give slightly differing outcomes in | | | | otherwise be expected (estimated 10-30% |
| each individual. Two environmental theories | | | | incidence). |
| include the impact of vaccines on the immune | | | | |
| system (of which a statistically significant | | | | Genetic component |
| link has never been found despite many | | | | |
| attempts; see the vaccine theory for a more | | | | Genetic influence comprises a significant |
| extensive treatment) and a more recent theory | | | | aspect of research in the causes of autism. A |
| relating autism to high levels of television | | | | large database showing theoretical links |
| viewing while young. A correlation has also | | | | between autism and genetic loci summarises |
| been found between autism and the mercury | | | | research indicating that the genetic |
| emitted from coal power plants, though the | | | | influence may extend to every human |
| implications of this correlation is | | | | chromosome. It has been observed in one |
| uncertain. Mercury measurements of hair | | | | twin-study in Britain that there was about a |
| samples from autistic children's first | | | | 60% concordance rate for autism in |
| haircuts were significantly lower than a | | | | monozygotic (identical) twins, while |
| matched group of normal children, declining | | | | dizygotic (non-identical) twins and other |
| as measures of severity increased. | | | | siblings comparatively exhibited about 4% |
| | | | concordance rates. Some research posits that |
| Research claims also link autism with | | | | the chances that an identical twin of an |
| abnormal blood vessel function, and oxidative | | | | autistic person will also be autistic are |
| stress. This line of research may lead to new | | | | 85-90%. The increased probabilities of |
| medical therapies. | | | | siblings having autism has been calculated at |
| | | | about 35-fold more than normal. |
| Physiology and neurology | | | | |
| | | | Accompanying impairments are also a common |
| Autism appears to involve a greater amount of | | | | feature of autism. Some people with autism |
| the brain than previously thought. A study of | | | | also have gastrointestinal, immunological or |
| 112 children (56 with autism and 56 without), | | | | neurological symptoms in addition to |
| published in the Journal of Child | | | | behavioral impairments. These associated |
| Neuropsychology, found those with autism to | | | | complexes have also lead to the search for |
| have more problems with complex tasks, such | | | | specific genetic connections and helped to |
| as tying their shoelaces or writing, which | | | | focus on reasonable genetic implications. |
| suggests that many areas of the brain are | | | | |
| involved. Children with autism performed | | | | Since genes provide the information for |
| simple tasks as well as or better than those | | | | processes and structure at the level of the |
| without. In tests of visual and spatial | | | | cell and its components during the growth and |
| skills, autistic children did well at finding | | | | development of a human as well as maintenance |
| small objects in complex pictures (e.g., | | | | during life, gene mutations (altered |
| finding the character Waldo in "Where's | | | | versions) and deletions (complete absence of |
| Waldo" pictures). However, they found it | | | | genetic material) and possibly extra copies |
| difficult to tell the difference between | | | | of genes would mean that the causes of autism |
| similar-looking people. Children with autism | | | | begin very early. If a mutated gene fails to |
| tended to do well in spelling and grammar, | | | | perform properly, then cells, proteins, |
| but found it much more difficult to | | | | enzymes and other crucial aspects of normal |
| understand complex speech, such as idioms or | | | | function may be significantly altered and |
| similes when the meaning of the phrase is | | | | operate incorrectly. Deletions could mean the |
| figurative. They would, for example, not | | | | complete absence of a sequence of events due |
| understand that "He kicked the bucket" meant | | | | to missing proteins or cell components for |
| someone had died, or were likely to actually | | | | example. These genetic alterations and |
| hop if told to "hop to it". | | | | deletions will simply bring about a changed |
| | | | structure or process which effects a great |
| The inference from this research, according | | | | many other needed structures and processes. |
| to researchers at the Pittsburgh School of | | | | |
| Medicine, is that "These findings show that | | | | Another important aspect of research in |
| you cannot compartmentalize autism. It's much | | | | genetic factors is environmental effects and |
| more complex.†| | | | the incidence of autism. During the lifetime |
| | | | of a person, gene mutations and deletions may |
| The research from this perspective has a | | | | be environmentally triggered or exacerbated. |
| number of implications: | | | | Conversely, it may also be that environment |
| | | | will not be a factor and nothing will change |
| Autism is more than likely a global disorder | | | | the autism characteristics. For autism, the |
| which affects how the brain processes the | | | | answer to these possible explanations is |
| information it receives, while complex | | | | still being researched and there is evidence |
| information tends to make this more readily | | | | that both may be true simply because there is |
| apparent. | | | | more than one way a person may develop |
| | | | autism. |
| Neurological ‘wiring’ in people | | | | |
| with autism manifest abnormalities in the | | | | Deletions and Mutations |
| areas of the brain that communicate with each | | | | |
| other. | | | | Deleted genes have been noted as a probable |
| | | | influence or cause in autism. By locating |
| Observed abnormalities provide a reasonable | | | | specific missing genetic material the |
| explanation for why children with autism have | | | | significance may be that specific genetic |
| problems with complex tasks which require | | | | sites for autism controlling or causing |
| multiple areas of the brain to work together; | | | | autism (autism susceptibility alleles) may be |
| autistic people tend to do better in tasks | | | | located precisely. Another significant aspect |
| that only require one region of the brain. | | | | of this research is that these deletions of |
| | | | genetic material indicate that autism may be |
| The causes of autism are possibly more | | | | established in some cases during meiosis |
| pervasive than previously believed; for | | | | (error-prone meiosis model) and this places |
| example, more areas of the brain are affected | | | | the genesis of autism in some at the very |
| than just those involving social interaction, | | | | beginning of life. |
| communication, interests, and imagination. | | | | |
| | | | One very important question in this line of |
| Autism may not be primarily a disorder of | | | | research is whether or not gene deletions are |
| social interaction; research must now take | | | | a cause or consequence of |
| into account non-social aspects. | | | | autism-susceptibility loci located elsewhere |
| | | | in the chromosomes. |
| A possible explanation for the | | | | |
| characteristics of the syndrome is a | | | | Gene mutations may mean a gene does not |
| variation in the way the brain itself reacts | | | | function at all or does not function in the |
| to sensory input and how parts of the brain | | | | normal way. Since genes direct how the body |
| then handle the information. An | | | | grows and develops, mutations, like |
| electroencephalographic (EEG) study of 36 | | | | deletions, will effect a person at the most |
| adults (half of whom had autism) at | | | | basic levels. |
| Washington University in St. Louis found that | | | | |
| adults with autism show differences in the | | | | Mutation and deletion effects have been |
| manner in which neural activity is | | | | delineated in numerous research publications. |
| coordinated. The implication seems to be that | | | | |
| there is poor internal communication between | | | | Correlated characteristics include global |
| different areas of the brain. | | | | developmental delay, mild to severe delay of |
| (Electroencephalographs, or EEGs, measure the | | | | speech, social communication disorders and |
| activity of brain cells.) | | | | cognitive abilities, autistic like behaviour, |
| | | | high tolerance of pain, and repetitive |
| The study indicated that there were abnormal | | | | mannerisms (e.g. chewing or mouthing). |
| patterns in the way the brain cells were | | | | |
| connected in the temporal lobe of the brain. | | | | Gene interaction may also complicate the |
| (The temporal lobe deals with language.) | | | | causes leading to multiple genetic origins of |
| These abnormal patterns would seem to | | | | autism, In a cascade like effect, when a gene |
| indicate inefficient and inconsistent | | | | loci is altered or omitted, others are |
| communication inside the brain of autistic | | | | effected due to change in interaction between |
| people. | | | | genes and/or their functions. |
| | | | |
| Studies in neuropathology indicate | | | | Though not present in all individuals with |
| abnormalities in the amygdala, hippocampus, | | | | autism, these mutations and deletions hold |
| septum, mamillary bodies, limbic system, and | | | | potential to point the way to more the |
| the cerebellum. | | | | genetic components of spectrum disorders. The |
| | | | research also advanced basic understanding in |
| Autistic brains are slightly larger and | | | | the genetic architecture of the genome of |
| heavier and a larger than normal head | | | | autistic individuals and will help in |
| circumference is commonly noted. | | | | focusing future research. |
| | | | |
| In the limbic system, there is an excess of | | | | One practical aspect of this type of research |
| cells and they are too small. The neurons | | | | may be the development of a test that would |
| themselves appear to be underdeveloped. | | | | confirm the autism diagnosis in children |
| Dendritic trees which provide the basis for | | | | exhibiting symptoms and identify families who |
| connections between neurons are truncated | | | | carry genetic defects that could be inherited |
| (i.e. shortened). | | | | by their children. |
| | | | |
| In the cerebellum, purkinje cells are widely | | | | Mirror neurons |
| affected. The anatomic differences correlate | | | | |
| to the curtailment of development earlier | | | | A theory featuring mirror neurons states that |
| than 30 weeks gestation. In other words, the | | | | autism may involve a dysfunction of |
| development of the cells appears to have | | | | specialized neurons in the brain that should |
| stopped at some time before the 30th week in | | | | activate when observing other people. In |
| utero | | | | typically-developing people, these mirror |
| | | | neurons are thought to perhaps play a major |
| An enlarged third ventricle of the brain | | | | part in social learning and general |
| appears to accompany autism in those who are | | | | comprehension of the actions of others. |
| non-mentally retarded, but the reasons for | | | | |