Is there any dna test for autism?

No: There are currently no available labs to test for autism.

No: But there are disease that can mimic autism that can be ruled out by dna type testing. Such diseases include fragile x, prader willi and smith-lemli-optiz (not really a dna test but it is a genetic disorder).

No, but there are >: 30 known syndromes in which autism & intellectual disability are part of the neurodevelopmental profile. If none of these is found by thorough history, physical & neurological exams, genetic microarray & dna probe for fragile x have replaced chromosome analysis because there's ~15% chance of finding an underlying genetic error vs. < 5% the old way.

Autism is a : Categorical diagnosis, based on observable behaviors that show qualitative impairments in social communication, reciprocal social interaction & stereotypical movements or narrow, restricted areas of interest. In addition to the genetic etiologies in my 1st answer, epigenetic factors that change fetal gene function, but not structure, include exposure to some viral infections & toxins.

No diagnostic test: But there likely exists a genetic predisposition, as autism in one child increases the risk of autism being diagnosed in the sibling. Also there are more and more genes being identified that may contribute to autism, with new mutations in these genes occurring more frequently in the sperm cells of older fathers.

No: In fact, nobody really knows what autism is. The diagnosis is often political, as children who are "different" for whatever reason may get far more government benefits if they are diagnosed with "autism" than with "learning disability" or the old "mental retardation." A few genes for classic autism are known but this is still a research area.

Not specifically: There is not a specific DNA test for autism, but there is genetic testing for many of the conditions that produce symptoms and behaviors like autism, for instance fragile X syndrome, Rett syndrome and many others.