The Prevalence of Neurofibromatosis Type 1 Among Children Identified with Autism Spectrum Disorders By the Autism and Developmental Disabilities Monitoring (ADDM) Network
Objectives: (1) to determine the prevalence of NF1 in a population-based sample of 8 year-old children with ASD, and (2) to identify and compare patterns of ASD criteria and related characteristics between children with ASD/NF1 and ASD only.
Methods: The Autism and Developmental Disabilities Monitoring (ADDM) Network identified 8-year-old children with ASD using validated population-based, multi-source records review methods during surveillance years 2000, 2002, 2004, 2006, and 2008. The ASD/NF1 group included ASD cases for which a NF1 diagnosis and/or ICD9 code (237.71) were indicated in their records. Differences in characteristics between ASD cases with and without NF1 were tested using χ2 and t-tests. Characteristics that were compared included sex, race/ethnicity, ID, ADHD, epilepsy, developmental regression, age of regression onset, ASD classification, ASD community diagnosis, and DSM-IV diagnostic criteria patterns. For DSM-IV criteria and pre-existing ASD community diagnosis comparisons, samples were restricted to surveillance years 2000, 2006, 2008 for which complete data were available.
Results: Among 12,271 children who met DSM-IV ASD diagnostic criteria, 22 (0.17%; 95% CI: 0.12%-0.27%) had NF1 /ASD. There was no difference in the distribution of sex or race/ethnicity between children with ASD/NF1 and ASD only. There was no difference in the frequency of history of regression or the co-occurrence of ID, ADHD, or epilepsy with ASD, although a lower frequency of co-occurring ID in children with ASD/NF1 than with ASD only was nearly statistically significant (p=0.06). Significantly fewer (p=0.04) children with ASD/NF1 had a previous ASD community diagnosis (53%), compared to children with ASD only (76%). Children with ASD/NF1 (58%) were significantly less likely (p=0.001) than those with ASD only (84%) to meet diagnostic criterion 1a (difficulty using or understanding non-verbal communication). A small difference was observed between ASD/NF and ASD groups in mean number of DSM-IV criteria met (8.4 and 8.9 respectively, p=0.44); no difference between groups was found in the median number of criteria (9).
Conclusions: The estimated NF1 prevalence among 8-year-old children with ASD was approximately 5 to 7 times higher than published general population prevalence estimates (1-in-3000 to 1-in-4000). The actual prevalence may exceed this because the presence of a co-morbid NF1 diagnosis is not consistently collected across ADDM sites. Among children with ASD/NF1, the lower prevalence of co-occurring ID and likelihood of a previously established community ASD diagnosis suggest that those with ASD/NF1 may have milder ASD manifestations than children with ASD only. These findings underscore the importance of regularly evaluating children with NF1 for ASD.