Prevalence of the fragile X anomaly amongst autistic twins and singletons

J Child Psychol Psychiatry. 1993 Jul;34(5):673-88. doi: 10.1111/j.1469-7610.1993.tb01064.x.


Early screening studies of autistic individuals suggested that up to one-quarter of cases were associated with the Fragile X anomaly. Recent studies find that the usual behavioural phenotype of the Fragile X anomaly is distinct from autism as usually defined, and that a variety of methodological factors contribute to the variability of the prevalence estimates. We report the prevalence of the Fragile X anomaly, using strict cytogenetic criteria, in a large sample of autistic individuals whose diagnosis was confirmed using a standardised diagnostic instrument. The anomaly was detected in 1.6% of tested autistic individuals from a combined sample of: autistic twins; clinic attenders; and, individuals from families multiplex for autism or related cognitive phenotypes. The anomaly was not detected in greater than 2.5% of any of the constituent samples and accounted for only a small proportion of the genetic influences amongst concordant twins and multiplex families. The anomaly was detected in 5% of the 40 tested autistic females, confirming reports that the prevalence of the anomaly is similar amongst autistic individuals of both sexes.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Autistic Disorder / complications*
  • Autistic Disorder / diagnosis
  • Autistic Disorder / epidemiology
  • Child
  • Child, Preschool
  • Chromosome Aberrations
  • Cognition
  • Comorbidity
  • Diseases in Twins / epidemiology*
  • Diseases in Twins / genetics
  • Female
  • Fragile X Syndrome / diagnosis
  • Fragile X Syndrome / epidemiology*
  • Fragile X Syndrome / genetics
  • Humans
  • Infant
  • Intellectual Disability / complications
  • Intellectual Disability / epidemiology
  • Intellectual Disability / genetics
  • Intelligence Tests
  • Interpersonal Relations
  • Karyotyping
  • Male
  • Middle Aged
  • Prevalence
  • Sex Factors