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).

This article may be too technical for most readers to understand. (June 2023)

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.^[1][2][3][4]

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.^[4][5] In most^[quantify] cases, its etiology is known.^[2][4]

Monogenic 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^[which?] syndromic forms of ASD can also have different^{[compared to?]} phenomenology.^{[clarification needed]}

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^[quantify] cases, its cause is polygenic.^{[citation needed]}

A 2017 study^[relevant?] 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.^{[4][clarification needed]}

Following the proposal, ASD would be divided into three genetic categories:^[4]

• Causes of autism
• Conditions comorbid to autism spectrum disorders