Some autistic individuals are also diagnosed with Fragile X Syndrome, which is a genetic condition involving changes in the long arm of the X chromosome. It causes a range of developmental problems including learning disabilities and mental retardation. And people suffered form Fragile X have dysmorphic facial features. This theory may explains why some autistic person are easy to recognize by facil traits, in the mean time, some have no visible physical characteristics of autism.
Autism spetrum is complex, including AS, Hyperlexia, Landau-Kleffner, PDD-NOS, Rett, Williams Syndrome, Fragile X Syndrome, and so on. Researchers have found out recently that about thirty percent of autism clinic population have several kind of these disorders at the same time. So dysmorphic facial features, helped the doctors to differentiate different autism. "Think of complex autism as being a sort of birth defect while essential autism is more of a biochemical disorder that may involve abnormalities of neurotransmitters," said Dr. Miles, who is a geneticist.
All autistic kids are different. We cannot say that they all have a particular facial or physical trait. Anyway, they are as beautiful as other children, there's not doubt about that.