Their son was only 11 months old when Dr. Eric London and his wife noticed something just wasn't right. "His babble wasn't progressing," says Dr. London, vice president of medical affairs at the National Alliance for Autism Research. "He wasn't making the more sophisticated sounds that are supposed to happen between 6 months and a year." Soon after, his son was diagnosed with autism.

Autism is a developmental abnormality that is classified as a pervasive developmental disorder (PDD), a relatively new title for a class of neurological disorders. According to a briefing paper put out by the National Information Center for Children and Youth with Disabilities, PDDs share the following characteristics: impairments in social interaction, imaginative activity, verbal and nonverbal communication skills and a limited number of interests and activities that tend to be repetitive.

Although PDDs are rare, the numbers have been steadily increasing since the 1970s. Previously estimated at four cases per 10,000 people, two recent studies have shown an incidence of 60 or more per 10,000. Although the difference is startling, it may be due to increased awareness and improved diagnostic measures rather than a true increased incidence of the disorder.

Five subsets of PDD have been identified: autism, Asperger's syndrome, childhood disintegrative disorder, Rett syndrome and PDDNOS (not otherwise specified).

Autism
Although autism is a term most parents have heard, the actual disorder is very rare. Dr. Robin Hilsabeck, a neuropsychologist and the director of cognitive programs at Texas Tech University Heath Services Center, estimates the incidence at approximately three or four people per 10,000. However, she fears, the disorder may be over-diagnosed.

Autism is difficult to identify because the symptoms vary greatly in type and intensity. Dr. Frank Aiello III, a developmental pediatrician at Children's Hospital of The King's Daughters, in Norfolk, Va., says diagnosing autism is similar to choosing a meal at a Chinese restaurant – you need a certain number of symptoms from column A, so many from column B, etc. There is no standard presentation. "You have to have some impairments, but they are not consistent and they cover a wider, broader area than other disorders," explains Dr. Hilsabeck. For this reason, autism and the other PDDs are often referred to as "spectrum disorders."

The key indicators of autism include difficulty communicating (both verbally and non-verbally), abnormal social relatedness, repetitive movements and/or speech, resistance to change and inappropriate play. Some children may also experience sensory sensitivities, aggressive or self-abusive behaviors and abnormal sleep patterns. Additionally, Danette Palomar, MA, LCPC, a child development specialist with Mount Sinai Hospital in Chicago, Ill., says, "Children with autism have increased risk for other developmental disabilities such as mental retardation, ADHD and seizures."

"At this point, the majority of children with autism are diagnosed sometime between 18 months and 2 ½ years," says Dr. London. However, he says, because of poor eye contact or lack of interest in being cuddled, some parents actually say they knew something was wrong with their child from birth.

Asperger's Syndrome
Children with Asperger's have symptoms that are similar to autism. Although their language is usually at or above age level, they often have severe social difficulties and very repetitive behaviors, interests and activities. They also experience delayed motor milestones and excessive clumsiness. Additionally, Dr. Hilsabeck states that Asperger's sufferers may have an increased incidence of mood disorders. "They are a little more aware, and they care," she says. "They just don't know how to interact or change their behavior."

Palomar explains that some individuals with Asperger's appear to be cognitively advanced because they learn to read early in their development. However, she says, they usually don't understand what they read. She says that, because of their good language and cognitive skills, many children with this disorder are not diagnosed until later in childhood.

Childhood Disintegrative Disorder
Childhood disintegrative disorder is also diagnosed later in childhood, usually after the age of 3. The symptoms for this disorder are almost identical to autism, but they don't begin until after at least two years of normal development.

Childhood disintegrative disorder is extremely rare and very severe. "These children are hit very, very hard," says Dr. London. Areas of regression include language and social ability, motor development, play skills and bladder and bowel functioning. "Not much is known about this disorder because it's so rare that it's hard to study," he says.

Rett Syndrome
Rett syndrome is another disorder where a child appears normal then gets progressively worse. However, the period of normal development is much shorter than in childhood disintegrative disorder. Usually, the child will lose previously acquired skills and begin demonstrating autistic-like behaviors around her first birthday.

Unlike the other PDDs, this syndrome most often affects girls. Also, while the other PDDs reach a certain level of impairment and then plateau, Rett sufferers continue to deteriorate, often resulting in shortened life spans. Fortunately, this is the most rare form of PDD.

PDDNOS
Pervasive developmental disorder not otherwise specified is the most common subset of the PDD classification. "This term is used to describe an individual who exhibits milder forms of social and communication impairments that are of a brief duration, develop later in life or are insufficient to categorize under another PDD diagnosis," says Palomar.

Diagnosis
Diagnosing PDDs is very difficult because of the varied symptoms and severity levels. Additionally, medical testing is usually not helpful in making the diagnosis. But, according to Palomar, genetic and neurological tests can rule out other syndromes before the diagnosis of PDD is given.

A child suspected of having a PDD should be evaluated by a variety of professionals, including a psychologist, speech-language pathologist, child development specialist and neurologist. "In addition to standardized psychological testing, behavioral and observational scales should also be completed," says Palomar. She adds that parental input and developmental history are also extremely important.

"There are many, many reasons why kids have symptoms like these," Dr. Hilsabeck says. "There are many other possibilities that need to be considered before you give a diagnosis of PDD." She further explains that the symptoms of PDD are also the symptoms of a number of other disorders. "It's only how they combine that you figure out which disorder it is," she says.

Prognosis
Although early and intense intervention can help children with PDDs improve their skills, the long-term outlook is not very promising. Because of their impaired communication and social skills, approximately 70 percent of children with PDDs will never be able to live on their own.

Unfortunately, Dr. London's son fits this statistic. At 14, he is very well behaved, but his language is still mediocre. When asked about his future, Dr. London says, "I don't think he'll ever live independently."

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