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Proposed Genetic Factors
Researchers have been interested in how genetics effect the development of ASD ever since the first autism twin study conducted by Folstein and Rutter in 1977, which found that the probability of identical twins having autism was statistically greater than for fraternal twins.6 The study of identical twins is significant because identical twins share essentially 100% of their genes. Further studies indicate that parents who have a child with ASD are 2% to 19% likely to have second child who is also affected by the disorder.7 For families with 2 or more children with autism the recurrence rate can reach approximately 35%.8 Studies have shown that approximately 10 to 15% of cases of autism can be linked back to a genetic cause.9 Because of the heritability of autism, physicians should require a family history of developmental disorders when a child undergoes his/her initial medical examination and may require genetic testing that “can provide information about any specific inherited problems, genetic defects, or nervous system abnormalities your child may have.”10
Researchers are longing to find the specific genes culpable for the development of ASD because if identified, at-risk children can begin early intervention immediately, before the signs of the disorder ever physically surface. Recent research has shown that about 10% of children with ASD can be subtyped due to genetic abnormalities.11 Genetic subtypes are invaluable because “genetic subtypes provide a greater degree of biological explanation for parents and families, and as such may facilitate identification of medical co-morbidities or clinical outcomes.”11 There is also evidence that suggest that some genes don’t necessarily cause autism, but can affect the degree of severity of the disorder. For example, researchers at the Johns Hopkins University School of Medicine have discovered a gene variant that seems to contribute to social interaction deficits in individuals with autism.12 Much of the research into genetics is accelerated by global research networks dedicated to collecting genetic material of individuals with autism and their families, determining how genes influence the development of autism, and searching for the specific genes that cause ASD.
While researchers investigate how certain different genes interact with their environment to influence the development of autism subtypes, there are already known forms that can be traced back to a single gene. For example, Fragile X Syndrome (FXS), the most common known “single gene” cause of autism, occurs when an individual has no FMR1 gene, which codes for the fragile-x mental retardation protein, which regulates the synthesis of other proteins at synapses.43-44 Due to its genetic origin, individuals can be diagnosed with FXS through a genetic test. The American Academy of Pediatrics stresses that families of children with autism test for other genetic abnormalities as it may lead to discoveries that can help improve the overall quality of treatment. According to a 2012 study, only about 30 percent of children with autism receive genetic testing.45
The Autism Genome Project (AGP) is a multi-phase project dedicated to identifying specific susceptibility genes for autism. Recent advancements in technology, like the DNA microarray, allow for the detection of some genetic changes involved in autism.13 Completed in 2007, Phase 1 of the Autism Genome Project pooled DNA data on 1,200 multiplex families for the use of further research. One-third of the data collected during this phase was donated by the Autism Genetic Resource Exchange (AGRE).14 Phase 2 of the project examined copy number variations (CNVs) and discovered that “there were numerous de novo and inherited events, sometimes in combination in a given family, implicating many novel ASD genes like SHANK2, SYNGAP1, DLGAP2, and the X-linked DDX53-PTCHD1.”15 According to Joe Piven, MD, a lead AGP consortium investigator “[i]dentifying the genes and biological pathways associated with these genes will eventually lead us to new treatment for autism based [on] an understanding of the underlying biological causes.”16 The discovery of new genes that influence autism can lead to earlier diagnosis and novel drug development by researchers.17 Despite this fact, the Autism Genome Project is currently waiting for funding for the program’s Phase 3.
The Autism Genetic Resource Exchange (AGRE) is a research program that focuses on collecting various types of data from families with two or more children on the autism spectrum.18 AGRE allows for “an unlimited number of scientists to join in the search for the factors that influence autism – discoveries that will lead us to more effective treatments, prevention, and possibly a cure for autism.”19 AGRE data was used in a recent twin study that concluded that the risk of concordance for ASD in identical twins is 70%, a dramatic decline from the 90% observed in smaller studies.20 This study demonstrates that prenatal environmental factors are playing a greater role in the development of ASD than science had previously realized.21 The over 2,000 families that have participated in AGRE have provided data for over 150 research groups worldwide that are working towards the treatment and prevention of ASD.19