Table 1

Demographics and clinical characteristics*

CharacteristicASDTDASD v. TD
t or χ2p value
Demographic characteristics
 Concordant twin pairs, n3034
  Age, yr, mean ± SD10.90 ± 2.809.59 ± 2.691.910.06
  Sex, M/F24/624/100.750.39
  Ethnicity, n3.270.51
   Asian22
   Black10
   Hispanic31
   White1927
   Multiple or other54
  Socioeconomic status†50.22 ± 11.8655.52 ± 8.60−2.030.05‡a
Clinical characteristics§
 Individuals, n9668
  Handedness, right/left85/1162/60.300.59
  Full-scale IQ, score86.40 ± 25.85112.99 ± 11.53−7.92< 0.001a,b
  RBS-R, total score19.50 ± 18.211.72 ± 3.767.87< 0.001a,b
  SRS, total score67.15 ± 17.4743.63 ± 5.4910.64< 0.001a,b,c,d
  ADI-R, diagnostic total33.99 ± 18.91———
  ADOS-2, comparison score6.27 ± 2.84———

  • ADI-R = Autism Diagnostic Inventory–Revised; ADOS-2 = Autism Diagnostic Observation Schedule, 2nd edition; ASD = autism-spectrum disorder; RBS-R = Restricted Behaviour Subscales–Revised; SD = standard deviation; SRS = Social Responsiveness Scale; TD = typically developing controls.

  • ↵* Samples included monozygotic and dizygotic twin pairs in which both twins were concordant for autism spectrum disorder (15 monozygotic and 15 dizygotic pairs) or were TD controls (20 monozygotic and 14 dizygotic pairs), or all individuals, including twin pairs that were discordant for ASD (4 monozygotic and 14 dizygotic pairs).

  • ↵† Hollingshead method: a 4-factor index of socioeconomic status calculated based on marital status, employment status, educational attainment and occupational prestige.

  • ↵‡ Significant 2-tailed comparison at p < 0.05.

  • ↵§ Restricted, repetitive behaviours and autistic mannerisms were assessed using the RBS-R and SRS, respectively. The ADI-R diagnostic total is the sum of the Social Interaction, Communication, and Restricted/Repetitive Behaviour subscales.

  • ↵ Significant at false discovery rate correction across the tests in each column.

  • ↵a Dizygotic ASD v. dizygotic TD, p ≤ 0.05

  • ↵b Monozygotic ASD v. monozygotic TD p ≤ 0.05

  • ↵c Monozygotic ASD v. dizygotic ASD p ≤ 0.05

  • ↵d Monozygotic TD v. dizygotic TD p ≤ 0.05