Symptoms of Autism and ADHD: a Swedish Twin Study Examining Their Overlap

Supplemental Materials

Symptoms of Autism and ADHD: A Swedish Twin Study Examining Their Overlap

by A. Ronald et al., 2014, Journal of Abnormal Psychology

http://dx.doi.org/10.1037/a0036088

Table S1

Loadings of ASD and ADHD Symptom Items in Principal Component Analyses

Component/Item / 1 / 2 / 3 / 4 / 5 / 6
Does s/he often have difficulty sustaining attention in tasks or play activities? / .723 / .306 / .038 / .068 / .163 / .182
Is s/he often forgetful in daily activities? / .705 / .015 / .163 / .207 / .037 / -.198
Does s/he often fail to pay close attention to details or make careless mistakes in schoolwork, or other activities? / .695 / .174 / .045 / .138 / .037 / .066
Is s/he often easily distracted or disturbed? / .687 / .198 / .072 / .169 / .203 / .107
Does s/he often avoid tasks that require sustained mental effort (such as homework)? / .685 / .163 / .138 / .040 / .157 / .154
Does s/he often lose things? / .677 / .017 / .150 / .270 / .026 / -.224
Does s/he have difficulty following instructions and to finish tasks? / .675 / .250 / .138 / .005 / .171 / .280
Does s/he often seem not to listen when spoken to directly? / .672 / .197 / .120 / .195 / .156 / .077
Does s/he often have difficulty organizing tasks and activities? / .666 / .233 / .217 / .029 / .219 / .220
Is s/he often “on the go” or does s/he often act as if “driven by a motor”? / .201 / .760 / .072 / .261 / .086 / -.021
Does s/he often run around and climbs more than his/hers peers? / .183 / .740 / .079 / .159 / .105 / .020
Does s/he have difficulty playing calmly and quietly? / .152 / .696 / .203 / .184 / .132 / .020
Does s/he have difficulties holding his/her hands and feet still or can s/he not stay seated? / .301 / .639 / .039 / .241 / .096 / .051
Does s/he get up and move about in school or in other situations when s/he is supposed to remain seated? / .311 / .587 / .126 / .204 / .161 / .080
Is he/she uninterested in sharing joy, interests, and activities with others? / .102 / .044 / .703 / .071 / .080 / .104
Does he/she have difficulties expressing emotions and reactions with facial gestures, prosody, or body language? / .094 / .123 / .666 / -.058 / .204 / .111
Does he/she exhibit considerable difficulties interacting with peers? / .183 / .116 / .639 / .076 / .229 / .160
Can he/she only be with other people on his/her terms? / .125 / .137 / .597 / .214 / .197 / -.035
Has he/she difficulties with games of make-believe or does he/she imitate considerably less than other children? / .104 / .050 / .519 / -.001 / .221 / .043
Does s/he often blurt out answers before the question has been completed? / .169 / .207 / .056 / .721 / .106 / .033
Does s/he talk excessively? / .123 / .187 / -.025 / .700 / .104 / .062
Does s/he often interrupt or intrude on others? / .227 / .284 / .139 / .691 / .137 / .062
Does s/he have difficulty awaiting turns? / .237 / .336 / .123 / .662 / .151 / .064
Does he/she get absorbed by routines in such a way as to produce problems for himself or for others? / .103 / .093 / .206 / -.010 / .694 / .004
Does he/she get obsessed by details? / .146 / .075 / .181 / .243 / .658 / .031
Does he/she dislike changes in daily routines? / .171 / .097 / .206 / .071 / .633 / -.011
Does he/she get absorbed by his/her interests in such a way as being repetitive or too intense? / .230 / .068 / .198 / .171 / .540 / .036
Has he/she ever engaged in strange hand movements or walking high on tiptoe when he/she was happy or upset? / .040 / .159 / .108 / .042 / .471 / .195
Was his/her language development delayed or doesn’t he/she speak at all? / .124 / .025 / .105 / .071 / .041 / .762
Does he/she have difficulties sustaining a conversation? / .131 / .010 / .465 / .033 / .100 / .547
Does he/she like to repeat words and expressions or does he/she use words in a way other people find strange? / .104 / .053 / .161 / .138 / .387 / .417

Note. Varimax rotation with Kaiser Normalization. Sex and age-groups combined. Loadings >0.40 in bold.

Table S2

Phenotypic Correlations Split by Age and Sex

Age 9 / SIs / CIs / RRBIs / INA / HYP / IMP
SIs / 1 / .22 / .30 / .30 / .25 / .28
CIs / .31 / 1 / .18 / .22 / .17 / .19
RRBIs / .40 / .27 / 1 / .31 / .26 / .33
INA / .33 / .26 / .38 / 1 / .45 / .47
HYP / .28 / .20 / .33 / .52 / 1 / .49
IMP / .29 / .19 / .39 / .46 / .53 / 1
Age 12 / SIs / CIs / RRBIs / INA / HYP / IMP
SIs / 1 / .28 / .38 / .32 / .28 / .29
CIs / .33 / 1 / .21 / .22 / .18 / .14
RRBIs / .42 / .29 / 1 / .36 / .31 / .37
INA / .31 / .27 / .41 / 1 / .40 / .42
HYP / .28 / .20 / .35 / .50 / 1 / .50
IMP / .29 / .22 / .40 / .45 / .55 / 1

Note. SIs, social impairments; CIs, communication impairments; RRBIs, restricted repetitive behaviors and interests; INA, inattention; HYP, hyperactivity, IMP, impulsivity. Male phenotypic correlations presented below diagonal, female above diagonal. All phenotypic correlations p<0.01.

Table S3

Observed and Expected Frequencies of 64 Symptom Combination Groupings for Males (Left Side of Table) and Females (Right Side of Table), and Significance Values

MALE / FEMALE
3956 / 3956 / 3912 / 3912
Cell / Observed / Total observed / Expected / Total expected / Chi/Fish / Observed / Total observed / Expected / Total expected / Chi/Fish
1a / 2605 / 1,351 / 2068.2318 / 1,887.7682 / 0.000 / 2972 / 940 / 2598.9238 / 1313.0762 / 0.000
2a / 14 / 3,942 / 79.4648 / 3,876.5352 / 0.000 / 6 / 3,906 / 53.0393 / 3858.9607 / 0.000
3a / 9 / 3,947 / 638.8778 / 3,317.1222 / 0.000 / 3 / 3,909 / 44.9458 / 3867.0542 / 0.000
4a / 472 / 3,484 / 77.2368 / 3,878.7632 / 0.000 / 442 / 3,470 / 613.5902 / 3298.4098 / 0.000
5a / 3 / 3,953 / 24.5467 / 3,931.4533 / 0.000 / 1 / 3,911 / 0.9173 / 3911.0827 / 1.000
6a / 17 / 3,939 / 2.9676 / 3,953.0324 / 0.000 / 14 / 3,898 / 12.5222 / 3899.4778 / 0.847
7a / 27 / 3,929 / 24.5467 / 3,931.4533 / 0.889 / 24 / 3,888 / 10.6114 / 3901.3886 / 0.042
8a / 6 / 3,950 / 0.9167 / 3,955.0833 / 0.130 / 3 / 3,909 / 0.2166 / 3911.7834 / 0.250
1b / 30 / 3,926 / 125.0150 / 3,830.9850 / 0.000 / 20 / 3,892 / 105.4714 / 3806.5286 / 0.000
2b / 1 / 3,955 / 4.8032 / 3,951.1968 / 0.221 / 0 / 3,912 / 2.1525 / 3909.8475 / 0.500
3b / 0 / 3,956 / 38.6172 / 3,917.3828 / 0.000 / 0 / 3,912 / 1.8240 / 3910.1760 / 0.500
4b / 24 / 3,932 / 4.6686 / 3,951.3314 / 0.000 / 29 / 3,883 / 24.9012 / 3887.0988 / 0.682
5b / 0 / 3,956 / 1.4837 / 3,954.5163 / 1.000 / 0 / 3,912 / 0.0372 / 3911.9628 / 1.000
6b / 0 / 3,956 / 0.1793 / 3,955.8207 / 1.000 / 4 / 3,908 / 0.5082 / 3911.4918 / 0.375
7b / 2 / 3,954 / 1.4421 / 3,954.5579 / 1.000 / 3 / 3,909 / 0.4306 / 3911.5694 / 0.250
8b / 2 / 3,954 / 0.0554 / 3,955.9446 / 1.000 / 1 / 3,911 / 0.0088 / 3911.9912 / 1.000
1c / 143 / 3,813 / 204.5503 / 3,751.4497 / 0.000 / 68 / 3,844 / 108.2885 / 3803.7115 / 0.003
2c / 5 / 3,951 / 7.8591 / 3,948.1409 / 0.579 / 0 / 3,912 / 2.2100 / 3909.7900 / 0.500
3c / 0 / 3,956 / 63.1857 / 3,892.8143 / 0.000 / 0 / 3,912 / 1.8727 / 3910.1273 / 0.500
4c / 33 / 3,923 / 7.6388 / 3,948.3612 / 0.000 / 17 / 3,895 / 25.5663 / 3886.4337 / 0.221
5c / 0 / 3,956 / 2.4276 / 3,953.5724 / 0.500 / 1 / 3,911 / 0.0382 / 3911.9618 / 1.000
6c / 2 / 3,954 / 0.2934 / 3,955.7066 / 0.500 / 3 / 3,909 / 0.5218 / 3911.4782 / 0.250
7c / 6 / 3,950 / 2.3596 / 3,953.6404 / 0.289 / 1 / 3,911 / 0.4421 / 3911.5579 / 1.000
8c / 4 / 3,952 / 0.0906 / 3,955.9094 / 0.125 / 3 / 3,909 / 0.0090 / 3911.9910 / 0.250
1d / 175 / 3,781 / 339.4886 / 3,616.5114 / 0.000 / 100 / 3,812 / 213.7643 / 3698.2357 / 0.000
2d / 6 / 3,950 / 13.0437 / 3,942.9563 / 0.167 / 1 / 3,911 / 4.3625 / 3907.6375 / 0.125
3d / 2 / 3,954 / 104.8682 / 3,851.1318 / 0.000 / 0 / 3,912 / 3.6968 / 3908.3032 / 0.375
4d / 119 / 3,837 / 12.6780 / 3,943.3220 / 0.000 / 85 / 3,827 / 50.4685 / 3861.5315 / 0.003
5d / 0 / 3,956 / 4.0292 / 3,951.9708 / 0.125 / 0 / 3,912 / 0.0754 / 3911.9246 / 1.000
6d / 9 / 3,947 / 0.4871 / 3,955.5129 / 0.004 / 5 / 3,907 / 1.0300 / 3910.9700 / 0.219
7d / 8 / 3,948 / 3.9162 / 3,952.0838 / 0.387 / 3 / 3,909 / 0.8728 / 3911.1272 / 0.625
8d / 8 / 3,948 / 0.1505 / 3,955.8495 / 0.008 / 2 / 3,910 / 0.0178 / 3911.9822 / 0.500
1e / 10 / 3,946 / 12.3641 / 3,943.6359 / 0.831 / 10 / 3,902 / 4.3946 / 3907.6054 / 0.179
2e / 0 / 3,956 / 0.4750 / 3,955.5250 / 1.000 / 0 / 3,912 / 0.0897 / 3911.9103 / 1.000
3e / 0 / 3,956 / 3.8193 / 3,952.1807 / 0.125 / 0 / 3,912 / 0.0760 / 3911.9240 / 1.000
4e / 5 / 3,951 / 0.4617 / 3,955.5383 / 0.062 / 5 / 3,907 / 1.0375 / 3910.9625 / 0.219
5e / 0 / 3,956 / 0.1467 / 3,955.8533 / 1.000 / 0 / 3,912 / 0.0016 / 3911.9984 / 1.000
6e / 1 / 3,955 / 0.0177 / 3,955.9823 / 1.000 / 3 / 3,909 / 0.0212 / 3911.9788 / 0.250
7e / 0 / 3,956 / 0.1426 / 3,955.8574 / 1.000 / 2 / 3,910 / 0.0179 / 3911.9821 / 0.500
8e / 1 / 3,955 / 0.0055 / 3,955.9945 / 1.000 / 1 / 3,911 / 0.0004 / 3911.9996 / 1.000
1f / 11 / 3,945 / 20.5205 / 3,935.4795 / 0.111 / 17 / 3,895 / 8.6751 / 3903.3249 / 0.169
2f / 2 / 3,954 / 0.7884 / 3,955.2116 / 1.000 / 0 / 3,912 / 0.1770 / 3911.8230 / 1.000
3f / 0 / 3,956 / 6.3388 / 3,949.6612 / 0.031 / 0 / 3,912 / 0.1500 / 3911.8500 / 1.000
4f / 23 / 3,933 / 0.7663 / 3,955.2337 / 0.000 / 18 / 3,894 / 2.0481 / 3909.9519 / 0.000
5f / 0 / 3,956 / 0.2435 / 3,955.7565 / 1.000 / 0 / 3,912 / 0.0031 / 3911.9969 / 1.000
6f / 9 / 3,947 / 0.0294 / 3,955.9706 / 0.004 / 5 / 3,907 / 0.0418 / 3911.9582 / 0.062
7f / 10 / 3,946 / 0.2367 / 3,955.7633 / 0.002 / 1 / 3,911 / 0.0354 / 3911.9646 / 1.000
8f / 11 / 3,945 / 0.0091 / 3,955.9909 / 0.001 / 2 / 3,910 / 0.0007 / 3911.9993 / 0.500
1g / 23 / 3,933 / 33.5757 / 3,922.4243 / 0.184 / 4 / 3,908 / 8.9068 / 3903.0932 / 0.266
2g / 5 / 3,951 / 1.2900 / 3,954.7100 / 0.219 / 1 / 3,911 / 0.1818 / 3911.8182 / 1.000
3g / 0 / 3,956 / 10.3715 / 3,945.6285 / 0.002 / 0 / 3,912 / 0.1540 / 3911.8460 / 1.000
4g / 30 / 3,926 / 1.2538 / 3,954.7462 / 0.000 / 8 / 3,904 / 2.1029 / 3909.8971 / 0.109
5g / 0 / 3,956 / 0.3984 / 3,955.6016 / 1.000 / 0 / 3,912 / 0.0031 / 3911.9969 / 1.000
6g / 9 / 3,947 / 0.0481 / 3,955.9519 / 0.004 / 1 / 3,911 / 0.0429 / 3911.9571 / 1.000
7g / 4 / 3,952 / 0.3873 / 3,955.6127 / 0.125 / 2 / 3,910 / 0.0364 / 3911.9636 / 0.500
8g / 8 / 3,948 / 0.0148 / 3,955.9852 / 0.008 / 1 / 3,911 / 0.0007 / 3911.9993 / 1.000
1h / 11 / 3,945 / 2.0295 / 3,953.9705 / 0.022 / 1 / 3,911 / 0.3615 / 3911.6385 / 1.000
2h / 2 / 3,954 / 0.0779 / 3,955.9221 / 0.500 / 0 / 3,912 / 0.0074 / 3911.9926 / 1.000
3h / 0 / 3,956 / 0.6269 / 3,955.3731 / 1.000 / 0 / 3,912 / 0.0063 / 3911.9937 / 1.000
4h / 23 / 3,933 / 0.0757 / 3,955.9243 / 0.000 / 6 / 3,906 / 0.0853 / 3911.9147 / 0.125
5h / 0 / 3,956 / 0.0241 / 3,955.9759 / 1.000 / 0 / 3,912 / 0.0001 / 3911.9999 / 1.000
6h / 7 / 3,949 / 0.0029 / 3,955.9971 / 0.016 / 4 / 3,908 / 0.0017 / 3911.9983 / 0.125
7h / 4 / 3,952 / 0.0234 / 3,955.9766 / 0.125 / 3 / 3,909 / 0.0015 / 3911.9985 / 0.250
8h / 15 / 3,941 / 0.0009 / 3,955.9991 / 0.000 / 6 / 3,906 / 0.0000 / 3912.0000 / 0.031
3956 / 2068.2318 / 1,887.7682 / 3912 / 3912

Note. Chi-square tests were used. Where expected frequencies were 1, Fisher’s exact test was used. Cells 1a–8h refer to the 64 possible ASD and ADHD symptom combinations as shown in Table 2. Significance criterion p<0.001.

Table S4

Twin Correlations Split by Age and Sex

Age 9 / Age 12
SIs / CIs / RRBIs / INA / HYP / IMP / SIs / CIs / RRBIs / INA / HYP / IMP
MZ / SIs / .48/.35 / .15 / .19 / .20 / .06 / .21 / SIs / .56/.43 / .22 / .18 / .29 / .22 / .25
CIs / .21 / .71/.66 / .14 / .20 / .12 / .13 / CIs / .29 / .75/.73 / .15 / .23 / .18 / .12
RRBIs / .30 / .21 / .49/.45 / .22 / .16 / .21 / RRBIs / .33 / .27 / .56/.49 / .33 / .19 / .29
INA / .26 / .21 / .31 / .54/.50 / .28 / .33 / INA / .29 / .23 / .34 / .57/.61 / .32 / .36
HYP / .23 / .16 / .28 / .38 / .58/.46 / .21 / HYP / .22 / .20 / .29 / .33 / .59/.50 / .40
IMP / .23 / .15 / .30 / .38 / .41 / .56/.52 / IMP / .24 / .21 / .33 / .36 / .42 / .61/.62
DZSS / SIs / .14/.15 / .12 / .09 / .18 / .12 / .11 / SIs / .14/.16 / .09 / .13 / .11 / .12 / .10
CIs / .10 / .33/.24 / .08 / .08 / .07 / .14 / CIs / .16 / .29/.30 / .09 / .07 / .09 / .09
RRBIs / .06 / .07 / .21/.20 / .24 / .19 / .18 / RRBIs / .10 / .14 / .27/.27 / .22 / .12 / .16
INA / .12 / .11 / .21 / .15/.17 / .15 / .25 / INA / .21 / .15 / .30 / .22/.17 / .03 / .15
HYP / .12 / .09 / .15 / .10 / .04/.08 / .17 / HYP / .13 / .14 / .20 / .16 / .07/-.03 / .02
IMP / .13 / .13 / .17 / .20 / .10 / .17/.25 / IMP / .08 / .15 / .19 / .21 / .11 / .15/.16

Note. SIs, social impairments; CIs, communication impairments; RRBIs, restricted repetitive behaviors and interests. INA, Inattention; HYP, Hyperactivity, IMP, Impulsivity; MZ, monozygotic; DZSS, dizygotic. Boys below diagonal, girls above diagonal.