I just want to clear up a couple of things I saw in a post or two before I answer the original post. Autism is a spectrum disorder and encompasses anything from the most mild of symptoms to the most severe. PDD means Pervasive Development Disorder, and NOS means Not Otherwise Specified and in itself, PDD and PDD-NOS are diagnoses of Autism Spectrum Disorders. Asperger's Disorder is form of Autism as well, and is often diagnosed with PDD-NOS. From Autism Speaks: "Autism is a general term used to describe a group of complex developmental brain disorders known as Pervasive Developmental Disorders (PDD). The other pervasive developmental disorders are PDD-NOS (Pervasive Developmental Disorder – Not
Otherwise Specified), Asperger's Syndrome, Rett Syndrome and Childhood Disintegrative Disorder. Many parents and professionals refer to this group as Autism Spectrum Disorders."
Okay. Two years old is very young to have an Autism diagnosis. Sometimes it's crystal clear and there's absolutely no doubt, but in most instances it's nearly impossible. Speech delays alone do not diagnose ASD (Autism Spectrum Disorder). You need to hit several points on the DSM-IV (diagnostic criteria http://www.autism-watch.org/general/dsm.shtml ). Small children in general can ALL "show signs" of autism but the difference is that most of them outgrow them. Most children with speech delays catch up with their peers. Most children with social delays or learning delays or motor skill delays or milestone delays catch up with their peers in a reasonable amount of time.
When my middle daughter was in preschool at 4 years old, it became very apparent when compared with her entire class that she had many, many delays in every single area of development. At home we thought she was just shy and developing at her own pace in comparison with her older sister who has always excelled and was reading without anyone actively teaching her at 3 years old. We had her informally evaluated by the school district and got her special services, then over summer break saw a child psychiatrist who diagnosed her with PDD-NOS and Asperger's Disorder. She had all of the classic signs.
Now at 8 years old and 2nd grade (we held her back for a 2nd year of preschool) she's been confirmed with the diagnosis by her old pediatric neurologist (she also has Seizure Disorder and Migraine Disorder as well as Sensory Processing/Integration Disorder), and recently by her new pediatric neurologist who specializes in Autism and Behavioral Disorders. Now that she's 8 years old it's more apparent that the ASD is more serious than we thought, and her diagnosis has actually tightened up quite a bit. She's still PDD-NOS but is more typical ASD than Asperger's Disorder.
So for us, it went the other way.
I also feel that I need to clear something else up as a mother to a child with ASD. ASD people not only CAN laugh, but they DO laugh. They have emotions and feel very strongly. They express emotions, sometimes very strongly, and sometimes it's difficult to read their emotions. That's part of the social concerns actually.
Anyway, what you want to do is check the DSM-IV but also trust your instincts. Early intervention is key in therapies and special services as they help teach our children coping skills for their entire lives about living in a world that doesn't think the same way they do.
People who can help diagnose: Pediatric Neurologist that specializes in ASD; Pediatric Psychiatrist/Psychologist; Pediatric Behavioral Specialist. You can also ask the school through Birth To Three to evaluate your child, although the school can NOT make a diagnosis as it's illegal for them to do so. They can point you in the right direction and make suggestions but not diagnose.
Here are some reliable sites for information to get you started.
http://www.cdc.gov/ncbddd/autism/screening.html
http://www.cdc.gov/ncbddd/autism/families.html
http://www.childbrain.com/pdd.shtml
http://www.autismspeaks.org/whatisit/index.php
http://learningdisabilities.about.com/od/assessmentandtes...
http://www.autism-society.org/about-autism/
EDITED TO ADD: I also feel that I need to address that most people with ASD are very intelligent. Many are average intelligence, and many are extremely intelligent. You can Google this, but there are a lot of famous artists and geniuses throughout history who are and were suspected to be ASD and are/were very successful.
There ARE more diagnoses of ASD now than there were before, and there are many misdiagnoses, but the fact that there are more people being diagnosed isn't because of misdiagnoses or more people have it but more research and more doctors being educated on the subject. More parents are educated about ASD now as well and are pushing for evaluations more than before. A lot of people who would have been "the eccentric one" in the family were very likely Autistic if people think back on their childhood behaviors and adult tendencies and behaviors. Autism being a spectrum disorder is also not so obvious as to be a "visible" disability. So you do have to trust your instincts, but it's very important to get to a qualified professional to begin evaluations outside of school.
Accept any special services you can from the school, because once you decline them and turn services away and don't have them any more it's going to be nearly impossible to get them back if it turns out you need them down the road.