TABLE 1. Twin sample demographics.

List of twin sample demographics. AP status: attention/hyperactivity status of twin pair; Twin pair: twin pair number; Age: age at time of MRI exam (in years); Sex: M = male, F = Female; AP scores: attention and hyperactivity problems for both twins measured with Child Behavior Checklist, AP high = T-score ≥ 60 at all available time points and ≥ 65 at least once; AP low = T-score ≤ 55 at all available time points; Mean AP T-score: mean AP T-scores across 2 or 3 time points (7, 10 and 12 years), computed separately for boys and girls; Aggression T-score: aggression T-scores from CBCL at age 12, separately for boys and girls. Anxious Depressed T-score: anxious depression T-scores from CBCL at age 12, separately for boys and girls; Birth weight: birth weight of each twin in grams; Incubation time: number of days spend in incubator; Comorbidities: at the time of MRI scanning, interview data were obtained from the mothers of the twins on items regarding dyslexia, social phobia, separation anxiety disorder, specific phobia, generalized anxiety disorder, depression, dysthymia, oppositional defiant disorder, and conduct disorder. For twin pairs 11 – 17 of the concordant CBCL-AP low controls interview data were not collected.

AP status	Twin pair	Age	Sex	AP scores	Mean AP T-score	Aggression T-score	Anxious Depressed T-score	Birth weight	Incubation time	Comorbidities
Concordant high	1	14.22	F	high/high	66.48/75.53	70.70/69.54	67.18/72.31	3270/2840	-	dyslexia/dyslexia
	2	18.35	F	high/high	67.51/73.16	66.36/60.67	57.87/65.65	1535/1430	28/28	no/no
	3	13.60	F	high/high	75.69/83.23	66.36/45.01	48.56/45.68	2350/2540	-	dyslexia/no
mean sd		15.39	3F		69.89/77.31	67.80/61.41	57.87/61.21	2385/2270
		2.58			5.05/5.26	2.51/7.79	9.31/13.86	868/743
Concordant low	1	17.27	M	low/low	39.45/39.81	39.46/39.57	45.70/46.03	2950/3045	-	no/no
	2	17.41	M	low/low	41.63/41.88	39.46/43.16	42.69/42.79	2500/2560	-/1.5	no/no
	3	15.93	F	low/low	44.52/40.83	40.33/40.70	42.35/45.68	3200/2830	-	no/no
	4	15.84	M	low/low	47.97/44.05	44.43/44.96	42.69/46.03	2580/2600	-	no/no
	5	15.47	F	low/low	49.78/48.73	44.67/47.36	48.56/45.68	1230/1590	32/25	no/no
	6	15.09	M	low/low	39.54/39.81	39.46/39.57	42.69/42.79	3000/2690	-/3	no/no
	7	14.84	M	low/low	42.71/39.81	42.77/41.37	42.69/42.79	3000/2800	-	no/no
	8	14.23	F	low/low	42.05/40.83	40.33/47.36	45.46/42.35	2830/2600	-	no/no
	9	14.64	F	low/low	40.65/40.65	53.34/47.36	42.35/42.35	2460/2680	-	dyslexia/dyslexia
	10	13.24	M	low/low	42.20/44.04	39.46/39.57	45.70/42.79	2670/2630	-	no/no
	11	16.75	F	low/low	42.06/42.14	40.33/40.70	42.35/42.35	2450/2660	-	no interview
	12	16.17	M	low/low	44.73/44.05	64.29/59.35	51.72/55.74	2480/2220	1/2.5	no interview
	13	15.54	F	low/low	42.05/42.11	42.50/42.92	42.35/42.35	1690/1590	23/24	no interview
	14	15.06	F	low/low	43.45/43.57	53.34/47.36	70.29/42.35	2330/2020	11/12	no interview
	15	14.71	F	low/low	46.26/49.13	55.51/49.57	57.87/49.01	2450/2190	1/1	no interview
	16	15.63	F	low/low	47.31/43.38	51.17/49.57	45.46/49.01	2720/3410	-	no interview
	17	16.27	F	low/low	43.03/42.88	57.68/47.36	42.35/55.66	2575/2550	-	no interview
mean sd		15.54	10F/7M		43.49/42.81	46.39/45.16	46.67/45.63	2536/2510
		1.08			2.92/2.75	7.86/5.13	7.39/4.42	479/469
Discordant	1	16.89	M	high/low	67.20/48.99	44.96/51.05	49.26/48.71	2470/2620	-	no/no
	2	15.99	M	high/low	69.65/46.07	44.43/39.57	45.70/42.79	2900/3000	1/1	no/no
	3	15.84	F	high/low	65.27/48.53	51.79/49.00	62.32/60.89	1400/2460	21/3	no/no
	4	14.70	F	high/low	63.77/42.06	80.63/44.67	78.96/45.46	1145/1360	21/44	no/no
	5	11.77	F	high/low	67.43/51.68	76.20/103.2	78.96/76.49	2315/2315	2/2	no/no
mean sd		15.04	3F/2M		66.66/47.47	59.60/57.51	63.04/54.89	2046/2351
		1.99			2.24/3.62	17.49/25.94	15.80/13.94	743/610