Autism Spectrum Disorder in Twins: Genetics Study

Introduction

Autism spectrum disorder (ASD) is a complex condition, and genetics play an important role as one of its causes. The current research shows that complex interactions involving genes and the environment are responsible for ASD (Yoo, 2015). The concordance rate of this disorder in monozygous twins is approximately 60-70 percent, and around 30 percent in siblings (Tick et al., 2016). Additionally, 50 percent of predisposing factors of ASD are believed to be associated with genetic variations (Yoo, 2015). These findings point to a clear link between genetics and ASD. Therefore, this section discusses the causes of autism, together with its origins, from a hereditary perspective.

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Chromosomal Analysis

In the first section of this report, a chromosomal analysis was not indicated. The information provided highlighted the link between ASD and genetics, but it did not explore the details concerning the involved genes and mutants, among other factors. Additionally, the first section raises some questions that will be addressed in this case report.

Causes of ASD

The main causes of ASD can be categorized into environmental and genetic factors. The hereditary aspects of this condition are explained using twin studies. In one of the earliest detailed studies on this topic, 11 monozygotic and 10 dizygotic twins were used as research subjects (Amaral, 2017). Out of the 11 monozygotic, four were concordant, which meant that they had autism (Amaral, 2017). On the other hand, none of the 10 dizygotic had autism. These results highlight the presence of genetic causes of ASD.

Environmental causes of ASD include exposure to naturally occurring pathogens. Maternal infection is one of the leading causes of autism. For instance, infection from maternal rubella during pregnancy is known to cause ASD (Amaral, 2017). Viral infections in the first trimester of pregnancy have shown a strong correlation with the diagnosis of this condition in the offspring (Tick et al., 2016). Another cause is autoimmune diseases during pregnancy, where maternal antibodies attack the fetus and cause brain damage. According to Amaral (2017), maternal antibody-related causes account for over 22 percent of autism cases. The use of some drugs during pregnancy, especially during the first and second trimesters, has also been shown to predispose fetuses to autism. Some of the drugs with severe effects include serotonin uptake inhibitors, valproic acid, and thalidomide, among others.

Researchers have extended investigations to cover the possibility of environmental toxicants. Ornoy, Weinstein-Fudim, and Ergaz (2015) note that exposure to motor air pollution, smoking, heavy metals, and some pesticides increases the risk of autism, albeit marginally. However, the relationship between ASD and environmental factors is still under study. Finally, some postnatal elements have been associated with this condition. For instance, a study conducted in a Romanian orphanage showed “the potential for severely abnormal rearing practices to influence brain regions that are affected by typical causes of autism” (Amaral, 2017, p. 9). However, research is underway to establish postnatal factors as causes of autism.

ASD’s Origin

The genetic origins of ASD are complex. However, the different variants of the condition can be traced to single gene inheritance. For instance, Rett’s syndrome, which is a severe form of autism, is caused by a mutation in MECP2 gene (Yoo, 2015). Similarly, Prader-Willi syndrome (another variant of ASD) is caused by chromosomal deletion of the paternal allele in 15q11-q13 (Ornoy et al., 2015). Yoo (2015) posits, “The genetic architecture of ASD is diverse in frequency (common vs. rare variation), mode of inheritance (inherited vs. de novo variation), type of variation (single nucleotide, indel, or copy number variation [CNV]), and mode of action (dominant, recessive, or additive)” (p. 258). Therefore, in practice and patient education, different gene mutations involved in this condition should be considered. The common gene variants associated with ASD include ASH1L, SYNGAP1, SHANK3, ARID1B, CHD8, POGZ, DYRK1A, and CHD2 (Yoo, 2015).

Gene Mutation of ASD

Syndromic autism is associated with particular gene mutations as opposed to idiopathic ASD, which has unknown causes. ARID1B has 13 known mutations that lead to autism. ASH1L has seven mutations, CHD2 has nine, CHD8 has more than 30, DYRK1A has 11, POGZ has 14, SHANK3 has 43, and SYNGAP1 has at least 5 (Yoo, 2015). The inheritance patterns of these genes are unknown. People with gene mutations that are associated with ASD tend to be highly predisposed to autism as opposed to inheriting the condition. Therefore, it is unknown whether gene mutations associated with autism are acquired or inherited.

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The common mutations of this condition occur by deletion or duplication. In deletion, one or more DNA base pairs are removed from a gene (Tick et al., 2016). On the other hand, duplication occurs when one or more DNA base pairs are copied abnormally, either once or severally.

Conclusion

ASD is a complex behavioral condition that is caused by genetic and environmental factors. Twin studies have been used widely to explain the hereditary nature of this condition. On the other hand, environmental causes of autism include maternal infection and autoimmunity, drugs, environmental toxicants, and postnatal factors. While the genetic architecture of this condition is complex, mutations can be traced to single genes. The common types of mutations include deletions and duplications. However, research has not established whether these genetic variations are inherited or acquired.

References

Amaral, D. G. (2017). Examining the causes of autism. Cerebrum. Web.

Ornoy, A., Weinstein-Fudim, L., & Ergaz, Z (2015). Prenatal factors associated with autism spectrum disorder (ASD). Reproductive Toxicology, 56, 155-169. Web.

Tick, B., Colvert, E., McEwen, F., Stewart, C., Woodhouse, E., Gillan, N., … Rijsdijk, F. (2016). Autism spectrum disorders and other mental health problems: Exploring etiological overlaps and phenotypic causal associations. Journal of the American Academy of Child & Adolescent Psychiatry, 55(2), 106-113.

Yoo, H. (2015). Genetics of autism spectrum disorder: Current status and possible clinical applications. Experimental Neurobiology, 24(4), 257-272.

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StudyCorgi. (2021, March 20). Autism Spectrum Disorder in Twins: Genetics Study. Retrieved from https://studycorgi.com/autism-spectrum-disorder-in-twins-genetics-study/

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StudyCorgi. (2021) 'Autism Spectrum Disorder in Twins: Genetics Study'. 20 March.

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