Autistic Girls More Likely to Go Undiagnosed Than Boys

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A recent study out in the Disability and Health Journal shows that girls are more likely than boys to remain undiagnosed. The study, by David Mandell’s group at the University of Pennsylvania, evaluated data from the Autism and Developmental Monitoring Network (ADDM). This is the same group that collects and analyzes data for the CDC’s autism prevalence studies.

Each ADDM study concentrates on children from a specific birth year. In this case, children born in 1994. They review records (medical, educational or both as available) to determine which children meet the criteria for autism. Some children already have a diagnosis of autism in their records. Other children are determined to be autistic via the ADDM review.

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Prof. Mandell’s group found that for those with existing diagnoses at the time of review, girls and boys were similar in terms of average age of diagnosis and first age of evaluation. However girls were more likely to be undiagnosed (medical or educational) at the time of the ADDM review.

Here is the abstract:

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Sex differences in the evaluation and diagnosis of autism spectrum disorders among children.

Giarelli E, Wiggins LD, Rice CE, Levy SE, Kirby RS, Pinto-Martin J, Mandell D.

Division of Biobehavioral Health Systems, University of Pennsylvania School of Nursing, Philadelphia, PA 19104, USA.

BACKGROUND: One of the most consistent features of the autism spectrum disorders (ASDs) is the predominance among males, with approximately four males to every female. We sought to examine sex differences among children who met case definition for ASD in a large, population-based cohort with respect to age at first developmental evaluation, age of diagnosis, influence of cognitive impairment on these outcomes, and sex-specific behavioral characteristics.

METHODS: We conducted a secondary analysis of data collected for a population-based study of the prevalence of ASD. The sample comprised 2,568 children born in 1994 who met the case definition of ASD as established by the Autism and Developmental Disabilities Monitoring (ADDM) Network for ASD surveillance. Children who had a history of developmental disability and behavioral features consistent with the DSM-IV-TR criteria for autistic disorder, Asperger’s disorder, and Pervasive Developmental Disorder-Not Otherwise Specified in existing evaluation records were classified as ASD cases via two paths: streamlined and nonstreamlined. Streamlined reviews were conducted if there was an ASD diagnosis documented in the records. Data were collected in 13 sites across the United States through the ADDM Network, funded by the Centers for Disease Control and Prevention.

RESULTS: Males constituted 81% of the sample. There were no differences by sex in average age at first evaluation or average age of diagnosis among those with an existing documented chart diagnosis of an ASD. Girls were less likely than boys to have a documented diagnosis (odds ratio [OR] = 0.76, p = .004). This analysis was adjusted for cognitive impairment status. In the logistic model, with the interaction term for sex and cognitive impairment, girls with IQ of 70 or less were less likely than boys with IQ of 70 or less to have a documented diagnosis (OR = 0.70, 95% confidence interval [CI] = 0.50-0.97, p = .035). Boys with IQ greater than 70 were less likely than boys with IQ of 70 or less to have a documented diagnosis (OR = 0.60, 95% CI = 0.49-0.74, p < .001). This finding (less likely to have a documented diagnosis) was also true for girls with IQ greater than 70 (OR = 0.45, 95% CI = 0.32-0.66, p < .001). Girls were more likely to have notations of seizure-like behavior (p < .001). Boys were more likely to have notations of hyperactivity or a short attention span and aggressive behavior (p < .01).

CONCLUSIONS: Girls, especially those without cognitive impairment, may be formally identified at a later age than boys. This may delay referral for early intervention. Community education efforts should alert clinicians and parents to the potential of ASDs in boys and girls.