Answer to Question 1
Many causes for the apparent dramatic increase in ASD have been proposedvaccines, mercury, diet, acetaminophen, caffeine, antibiotics, allergies, environmental pollutants, and electromagnetic radiationbut to date, none has been scientifically substantiated. It seems likely that most, if not all, of the rise in prevalence is caused by a greater awareness among parents and professionals; a broadening of the concept and its definition over the years; greater recognition and diagnosis of milder forms of ASD; changes in diagnostic criteria and categories; diagnostic substitution (i.e., the number of children receiving special education under other diagnostic categories, primarily ID, speech impairment, and learning disabilities, has decreased as those diagnosed with ASD have increased); and better case-finding methods
Answer to Question 2
The discovery of the fragile-X anomaly (see Chapter 5) in about 2 to 3 of children with ASD led to increased attention to this and other chromosomal defects that might be related to ASD. Some studies have found that as many as 15 to 20 of siblings of individuals with ASD also have the disorder, a number nearly twice that seen in earlier reports. New research using molecular genetics has pointed to particular areas on many different chromosomes as possible locations for susceptibility genes for ASD (Klinger et al., 2014). Susceptibility genes are causally implicated in the susceptibility to ASD but do not cause it directly on their own.
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