Genetics of autism

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Genetics of autism

Jun112019

Is autism genetic?

For a long time it has been presumed that there is a common cause in the genetic, cognitive and neural levels of the triad of symptoms characteristic of autism. However, there is a growing suspicion that autism is a complex disorder whose central aspects have different causes that often occur simultaneously (2,3).

Autism has a solid genetic basis, although the genetics of autism is complex and it is not clear if ASD is more explained by rare mutations with greater effects, or by rare multigenic interactions of common genetic variants (4,5).

The complexity arises due to the interactions between multiple genes, the environment and epigenetic factors that do not change the sequencing of DNA, but are hereditary and influence gene expression. Many genes have been associated with autism by sequencing the genomes of affected people and their parents.

Studies of twins and family members show that autism is a highly hereditary condition, but they have left many questions for researchers

There are many pending questions to be resolved in patients, which until now we know is that most of the mutations that increase the risk of autism have not been identified. In general, autism can not be attributed to a Mendelian mutation (of a single gene) or to an anomaly of a single chromosome, and it has not been demonstrated that none of the genetic syndromes associated with ASD selectively causes ASD.

The large number of autistic individuals with unaffected family members may be the result of spontaneous structural variation, such as deletions, duplications or investments in genetic material during meiosis. Therefore, a substantial fraction of autism cases can be attributed to genetic causes that are highly inherited but not inherited: that is, the mutation that causes autism is not present in the parental genome. Autism may be under-diagnosed in women and girls due to the assumption that it is mainly a male condition.

Chromosomal alterations

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estudio genetico — autismo genolife estudio genetico

Characteristics of the autistic spectrum

Spectrum disorder (ASD) is a condition that appears very early in childhood development, varies in severity and is characterized by poor social skills, communication problems and repetitive behaviors. These difficulties can interfere with the ability of affected individuals to function in social, academic and work environments.

People with ASD also have an increased risk of psychiatric problems, such as anxiety, depression, obsessive-compulsive disorder, and eating disorders. From the age of 1 to 2 years, people with ASD have a reduced ability to interact with other people; they often feel more comfortable dealing with objects. Affected people have difficulty understanding and using nonverbal social cues, such as eye contact, facial expressions, gestures and body language. The inability to recognize and use these signals makes it difficult for affected people to understand the feelings of others or communicate their own feelings in an appropriate way.

For most children with autism, the symptoms develop gradually, although approximately 30% have a “regressive” onset usually between 18 and 24 months. About 50% -70% of children with autism are identified as people with intellectual disabilities, through tests of non-verbal IQ and about 25% develop seizures.

Autism may be considered complex (ie, the presence of dysmorphic features and / or microcephaly) or essential (ie, absence of physical abnormalities and microcephaly). About 25% of children who meet the diagnostic criteria for ASD at the age of two or three years later, begin to speak and communicate, and by the age of six to seven years is mixed in different grades in the school population regular. The remaining 75% have lifelong disabilities that require intensive parental, school and social support.

Environmental factors associated with autism

Maternal nutrition and inflammation during preconception and pregnancy influence fetal neurological development. Intrauterine growth restriction is associated with ASD, both in full-term and premature infants. Maternal inflammatory and autoimmune diseases can damage fetal tissues, aggravating a genetic problem or damaging the nervous system.

Exposure to air pollution during pregnancy, especially heavy metals and particles, may increase the risk of autism. Environmental factors that have been asserted without evidence of contributing or exacerbating autism include certain foods, infectious diseases, solvents, PCBs, phthalates and phenols used in plastic products, pesticides, brominated flame retardants, alcohol, tobacco, illicit drugs, vaccines and prenatal stress among the main ones.

Other common conditions in children with symptoms of autism

Genetic disorders. About 10 to 15% of autism cases have an identifiable Mendelian condition (single gene), chromosomal abnormality or other genetic syndrome and ASD is associated with several genetic disorders.

Intellectual disability. It has been reported that the percentage of autistic individuals who also meet the criteria for intellectual disability ranges between 25% and 70%, a wide variation that illustrates the difficulty of assessing the intelligence of individuals in the spectrum of autism. In comparison, for PDD-NOS the association with intellectual disability is much weaker and, by definition, the diagnosis of Asperger excludes intellectual disability.

Anxiety disorders are common among children with ASD; there are no firm data, but studies have reported prevalences ranging from 11% to 84%. Many anxiety disorders have symptoms that are better explained by the ASD itself, or are difficult to distinguish from the symptoms of ASD.

Epilepsy, with variations in the risk of epilepsy due to age, cognitive level and type of language disorder.

Several metabolic defects, such as phenylketonuria, are associated with autistic symptoms.

References

Geschwind DH (2009). “Advances in autism”. Annu Rev Med. 60: 367–80. doi:10.1146/annurev.med. PMID 19630577.
Happé F, Ronald A (2008). “The ‘fractionable autism triad’: a review of evidence from behavioural, genetic, cognitive and neural research”. Neuropsychol Rev. 18 (4): PMID 18956240.
Happé F, Ronald A, Plomin R (2006). “Time to give up on a single explanation for autism”. Nature Neuroscience. 9 (10): 1218–20. PMID 17001340.
Abrahams BS, Geschwind DH (May 2008). “Advances in autism genetics: on the threshold of a new neurobiology”. Nature Reviews. Genetics. 9 (5): 341–55. PMC 2756414. PMID 18414403.
Buxbaum JD (2009). “Multiple rare variants in the etiology of autism spectrum disorders”. Dialogues in Clinical Neuroscience. 11 (1): 35–43. PMID 19432386.

Leagues of interest

A Review of Functional and Structural Neurobiology of the Action Observation Network in AutismSpectrum Disorder and Developmental Coordination Disorder. https://www.mdpi.com/2076-3425/9/4/75

Sensory perception in autism. https://www.nature.com/articles/nrn.2017.112

Molecular karyotype directed to autism

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