Autistic Disorder occurs four times more frequently in boys than girls and is characterized in some children by withdrawn behaviour or other unusual social behaviours, problems using language to communicate, repetitive patterns of behaviour and the inability to engage in imaginative play. Usually the child begins with normal development and shows regression between 12 and 24 months of age.

Many experts view Asperger's Disorder as high-functioning autism. Children with Asperger's Disorder have no significant delays in language skills or in cognitive development, self-help skills or adaptive behaviour. There is, however, significant impairment in social functioning as well as stereotyped behaviours and repetitive mannerisms.

Not otherwise Specified (PDD-NOS) occurs when a child may not fall within the realm of other ASD's, but nonetheless shows signs of severe and pervasive impairment in the development of reciprocal social interaction, verbal and non-verbal communication skills.

Rett's Disorder has only appeared in girls to date. These children seem to develop normally until between 5-18 months, then experience a deceleration of head growth and lose previously acquired language. Hand skills are replaced by stereotypical behaviour (hand-flapping, wringing). There is also a loss of social interaction, physical coordination and receptive and expressive language is impaired. Recently, a genetic marker for Rett's syndrome has been identified.

Childhood Disintegrative Disorder (CDD), also known as Heller's Disease, refers to the normal development of children until 2 years of age, who then lose acquired skills. This usually occurs between 36 and 48 months of age but may occur up to 10 years of age.

Landau-Kleffner Syndrome (LKS) or Acquired Childhood Epileptic Aphasia is not as common as autism but can occur with autism, especially along with Childhood Disintegration Disorder. Although children with LKS demonstrate much behaviour similar to autism, in all cases children with LKS have abnormal electroencephalogram (EEG), stemming from abnormal brain activity. Seizures occur in approximately 80% of the cases, often only during sleep. Besides typical seizure symptoms, other types of seizures include staring spells, drooling, odd movements or smacking with the mouth, night waking, and night terrors. Hyperactivity, anxiety, aggressiveness, and depression are often associated with LKS.

If you have any cause to suspect LKS, contact a child neurologist as soon as possible. According to experts, LKS is often misdiagnosed as autism and is treatable with medications or surgery if diagnosed in its early stages.

In North America, most children are screened soon after birth for Phenylketonuria, or PKU, a genetic disorder involving the inadequate metabolism of the amino acid phenylalanine. If a child is diagnosed with this disorder then a phenylalanine free diet is prescribed. Brain damage can occur fi the diet is not followed, resulting in mental retardation and some autistic behaviours. If your child has not been tested for PKU, have your doctor do this simple test to rule out this disorder.

Fragile X Syndrome results from an abnormality of the DNA molecules of the sex chromosome X. It often causes mental retardation and has associated autistic symptoms. Individuals with Fragile X Syndrome are often hypersensitive to sights, sounds, smells, and tactile stimuli. They commonly engage in hand flapping, avoid eye contact, have tactile defensiveness and perseverative speech. Physicians routinely test to rule out Fragile X Syndrome during early stages of autism diagnosis.