Autism Spectrum Disorder (ASD) is a heterogeneous neurodevelopmental disorder whereby the patient exhibits three main characteristics: impaired communication, poor social interaction, and language delay. Uncontrollable repetitive actions also characterize it. In addition to the main symptoms, ASD patients have comorbidities in gastrointestinal disorders, intellectual disability, epilepsy, sleeplessness and immune disorders. Autism Spectrum Disorders occurs in three subtypes which are based on the severity of the clinical symptoms. The factors causing the disorder can be understood by looking at the family study, twin study and cytogenetic abnormality.
Research has shown that when a family has an autistic child, the possibility of other children being born with the disorder increases 25 times as compared to other families without ASD children (Almandil et al., 2019, p. 658). However, most of these children diagnosed with ASD disorder are also diagnosed with other genetic and neurologic disorders. They include fragile X syndrome, phenylketonuria, and other congenital disorders related to the rubella virus cytomegalovirus (Almandil et al., 2019, p. 658). Autism Spectrum Disorders are also said to aggregate in families, but it is unknown to what extent the genetic factors or the shared and non-shared environment contribute (Ornoy et al., 2016, p. 316).
Families with autistic patients may have a higher risk of having children with the disorder. This can be mainly because the parents may be having a genetic disorder. Therefore, even a family which has had no prior history of having ASD patients also have a risk in future. The risk can be increased due to structural variations or gene mutations in the parents, leading to having a child with the disorder and even other related postnatal neurodevelopmental disorders.
Twin studies have suggested that the identical (monozygotic) twins have a higher chance ranging from 60-90 % concordance rate of being diagnosed with autism disorder. The dizygotic (fraternal) twins have a lower risk of 0-24% of having the condition. The early twin studies have pointed out that ASD has the highest chance of heritability compared to all other developmental disorders (Chaste & Leboyer, 2012, p. 281). This is due to the high proportion of phenotype variance due to genetic factors estimated to be about 90 %. Other twin studies have indicated the substantial roles that shared environmental influences have in increasing or decreasing the chances of twins diagnosed with ASD (Todorov et al., 2013, p. 137).
Since identical twins share the same DNA, they have a higher chance of both being born with ASD disorder. The fraternal twins only share 50 % of the DNA and have a lesser chance of both being born with the disorder. However, structural variations and mutations can alter the DNA of one of the twins causing one to be born healthy while the other twin has the condition.
Cytogenetic analysis is a scientific genetic approach aimed at studying the contribution of chromosomal aberrations in children’s disorders. The hypothesis for these tests has shown that autism is mainly due to sporadic mutations and not heritability (Almandil et al., 2019, p. 658). However, with the disorder being heterogeneous, it becomes challenging to identify the specific genetic factors that cause it. Numerous networking approaches are required to identify the specific loci in the DNA that are responsible for ASD.
Few studies have delved into the study of genetic factors associated with ASD. The few studies that have been involved have had both advantages and limitations. Even though genetic mutations play a key role in chromosomal abnormalities, other hypothetical risk factors such as neurodevelopmental disorders can be linked with socioeconomic factors like drug abuse and parental mental health disorders to increase the risk of ASD.
In all the studies discussed above, the influence of genetics seems to be the major factor associated with ASD. The studies point out the structural variations and mutations being the main cause. However, most prior studies have had limitations due to the use of a small sample size for the research, resulting in unreliability. The studies also have mainly used randomly picked samples, which has raised the concern of possible biases introduced by population selection.