Syndromic autism (or syndromic autism spectrum disorders) denotes cases of autism spectrum disorder that are associated with a broader medical condition, generally a syndrome. Cases without such association, which account for the majority of total autism cases, are known as ''non-syndromic autism'' (or ''non-syndromic autism spectrum disorders''). Studying the differences and similarities (e.g. common pathways) between syndromic and non-syndromic cases can provide insights about the pathophysiology of autism and pave the way to new

autism therapies The autism spectrum, often referred to as just autism or in the context of a professional diagnosis autism spectrum disorder (ASD) or autism spectrum condition (ASC), is a neurodevelopmental condition (or conditions) characterized by difficulti ...

Syndromic autism

Autism spectrum disorder (ASD) is referred to as syndromic when it is one of the many characteristics associated with a broader medical condition, generally a syndrome. Syndromic autism represents about 25% of the total ASD cases. In most cases, its

etiology Etiology (pronounced ; alternatively: aetiology or ætiology) is the study of causation or origination. The word is derived from the Greek (''aitiología'') "giving a reason for" (, ''aitía'', "cause"); and ('' -logía''). More completely, e ...

is known.

Monogenic disorders A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosomal abnormality. Although polygenic disorders ...

are one of the causes of syndromic autism, which in this case are also known as ''monogenic autism spectrum disorders.'' They account for about 5% of the total ASD cases. Certain syndromic forms of ASD can also have different phenomenology.

Non-syndromic autism

Non-syndromic autism, also called ''classic autism'' or '' idiopathic autism'' (as in most cases, the etiology is unknown), represents the majority of total autism cases. In most cases, its cause is polygenic.

Classification

A 2017 study proposed to replace the classification "syndromic"/"non-syndromic" ASD into one based on the genetic etiology of the condition, specifying if the syndromic condition occurs in the context of a "'' phenotype first''" clinically defined syndrome or from a "'' genotype first''" molecularly defined syndrome. Following the proposal, ASD would be divided into three genetic categories:

Clinically defined

Syndromes recognized by clinicians (depending on their experience), typically confirmed by a targeted

genetic testing Genetic testing, also known as DNA testing, is used to identify changes in DNA sequence or chromosome structure. Genetic testing can also include measuring the results of genetic changes, such as RNA analysis as an output of gene expression, or ...

. *Chromosomal (e.g.: Down syndrome) *Syndromes caused by mutations in single genes (e.g.:

NF1 Neurofibromin 1 (''NF1'') is a gene in humans that is located on chromosome 17. ''NF1'' codes for neurofibromin, a GTPase-activating protein that negatively regulates RAS/MAPK pathway activity by accelerating the hydrolysis of Ras-bound GTP. ''N ...

, TSC, PTEN-associated macrocephaly syndrome, some males with FXS) *Syndromes caused by CNVs (e.g.: microdeletion 22q11.2 syndrome) *Teratogens (e.g.: valproate aembryopathy)

Molecularly defined

Syndromes recognized by genome-wide testing, not by hypothesis-driven testing (since clinical recognition is difficult). *Chromosomal (e.g.:

isodicentric 15 Isodicentric 15, also called marker chromosome 15 syndrome, idic(15), partial tetrasomy 15q, or inverted duplication 15 (inv dup 15), is a chromosome abnormality in which a child is born with extra genetic material from chromosome 15. People wit ...

q) *ASD-risk genes (e.g.: ADNP, ARIDB1B, ANK2, SCN2A) *ASD-associated CNVs (e.g.: 16p11.2 deletion/duplication, exonic NRXN1 deletions)

Currently undefined

Currently undefined.

References

{{DEFAULTSORT:Syndromic autism Syndromes with autism