SLC6A4 and autism: For example, in a 6‐week open label trial with 44 participants with autism, two increasing daily doses of the SSRI escitalopram resulted in improvement on insistance of sameness and irritability symptoms irrespective of whether individuals had polymorphisms of 5‐HTT (SLC6A4) or of the 5‐HT2A receptor (HTR2A).