Syndromic autism (or syndromic autism spectrum disorder) denotes cases of autism 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 disorder).
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.
Syndromic autism represents about 25% of the total ASD cases. In most cases, its etiology is known. 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. SCN2A is the leading monogenic cause of autism.
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 genetic categories, including:
Syndromes recognized by clinicians (depending on their experience), typically confirmed by a targeted genetic testing.
Syndromes recognized by genome-wide testing, not by hypothesis-driven testing (since clinical recognition is difficult).