Childhood Neuropsychiatric Disorders on the Rise

AARHUS, Denmark, Feb. 5 -- Four common neuropsychiatric disorders of childhood appear on the rise, with Tourette's syndrome, and hyperkinetic disorder joining autism and autism spectrum disorder, researchers here reported.

In a study of records on 670,000 Danish children born in the 1990s, there were statistically significant increases in cumulative incidence across specific birth years for all four conditions, reported Hjrds sk Atladttir, M.B., of the University of Aarhus. and colleagues in the February issue of the Archives of Pediatrics & Adolescent Medicine.

There was no increase in the incidence of obsessive-compulsive disorder over the same period, however, the investigators reported.

"Although the reasons for the observed common pattern of change in reported cumulative incidence in Tourette's syndrome, hyperkinetic disorder and autism spectrum disorder cannot be addressed with these data, it is clear that the number of children with neuropsychiatric disorders and their families in need of support and services has been growing in recent years," the authors wrote.

"Furthermore, while the search for causes should proceed unabated, the ultimate value of these data are their contribution to the growing awareness of child neurodevelopment problems in general and understanding of the resources needed to ensure optimal development for all children," they continued.

The authors proposed two models to explain the observed increases. One possibility is that the pattern of increase is coincidental, and that independent disease factors are causing the rise in incidence of each condition.

Alternatively, there may be one or more shared factors, such as genetics, environment, diagnostic shift, or a combination of these factors.

The authors drew on Denmark's renowned national health care data banks, linking information from the Danish Medical Birth Registry with data from the Danish National Psychiatric Register. The latter database included diagnoses recorded by psychiatrists using standardized diagnostic codes (ICD-10).

They looked at records on all 669,995 children born in Denmark from 1990 through 1999. The primary study outcome was the cumulative incidence proportions of each of the targeted disorders:

• Autism spectrum disorders
• Childhood autism (a subset of autism spectrum disorders)
• Tourette's syndrome
• Hyperkinetic disorder
• Obsessive-compulsive disorder.

The data were stratified by age and year of birth for each disorder, grouped into birth cohorts spanning two years.

The investigators identified 4,376 children who received a total of 4,637 diagnoses.

The diagnoses of hyperkinetic disorder, Tourette's syndrome and autism spectrum disorder all showed statistically significant tests for trend.

"For hyperkinetic disorder, an increase in cumulative incidence was observed across all cohorts such that each successive birth cohort had a significantly higher cumulative incidence than the previous cohort (P<0.001)," the authors wrote. "For example, at 5 years of age the cumulative incidences of hyperkinetic disorder for the 1994-1995 cohort, 1996-1997 cohort, and 1998-1999 cohort were 26%, 100%, and 200% higher, respectively, than the cumulative incidence for the 1992-1993 cohort."

Similarly, the 1994-1995 birth cohort had a significantly higher cumulative incidence of Tourette syndrome than either the 1990-1991 cohort (P=0.005) or the 1992-1993 cohort (P=0.006), although there was no significant change from children born in 1990 through 1993 in cumulative incidence of Tourette's.

Looking at autism spectrum disorders overall, they found that the 1998-1999 birth cohort had significantly higher cumulative incidence proportions than the 1994-1995 birth cohort (P=0.004), but there were no other significant differences among the various birth cohorts.

Looking only at those with a diagnosis of childhood autism (38% of all children with autism spectrum disorders), the investigators found that the cumulative incidence proportion was significantly higher for children in the 1998-1999 birth cohort than those born either from 1994-1995 (P<0.001) or 1996-1997 (P=0.02).

There was no significant change in autism incidence, however, between the 1994-1995 and 1996-1997 birth cohorts.

The authors did not find any significant difference across the various birth cohorts in the cumulative incidence proportions for obsessive-compulsive disorder.

"It is difficult to explain why obsessive-compulsive disorder was the only disorder displaying another pattern; the reason may be etiologic, due to non-etiologic diagnostic differences, or due to the relatively short follow-up," they wrote.

Their results support earlier findings of time trends in the increase of autism, and suggest that if "the debate surrounding explanations for the increase in autism incidence should also consider the evidence of a more widespread epidemiologic phenomenon across different diagnostic conditions," the investigators stated in their conclusion.