Table 1 Baseline characteristics of children with ADHD separated according to genotype in the triallelic 5-HTTLPR polymorphism of the SLC6A4 gene.

Age

8.9 (1.80)

9.2 (1.90)

8.8 (1.70)

F_2,154 = 0.7, p = 0.52

Males/Females (% males)

30/12 (78%)

67/14 (88.5%)

34/0 (87.5%)

χ² = 11.2, df = 2, p = 0.003

Household income (% < $20,000 per year)

41.5%

31.6%

44.8%

χ²= 1.9, df = 2, p = 0.38

Ethnic origin (Caucasian/non-Caucasian)

35/7

72/9

30/4

χ² = 0.8, df = 2, p = 0.92

WISQ-III full scale IQ

96.9 (15.4)

99.3 (15.2)

97.3 (14.5)

F_2,144 = 0.4, p = 0.69

CBCL

   Total score

69.4 (9.4)

69.5 (10.3)

70.4 (6.9)

F_2,149 = 0.1, p = 0.88

   Internalizing problems

65.2 (11.8)

64.5 (12.3)

62.4 (8.6)

F_2,149 = 0.6, p = 0.54

   Withdrawn

64.1 (11.7)

64.2 (10.7)

61.4 (7.6)

F_2,149 = 0.9, p = 0.41

   Somatic complaints

61.3 (8.5)

59.3 (8.5)

56.9 (7.0)

F_2,149 = 2.4, p = 0.10

   Anxiety/depression

65.1 (10.6)

66.3 (11.9)

63.0 (8.8)

F_2,149 = 1.1, p = 0.34

   Social problems

65.8 (10.6)

67.6 (10.6)

68.0 (10.6)

F_2,149 = 0.5, p = 0.60

   Thought problems

63.0 (11.1)

63.5 (10.8)

62.5 (9.5)

F_2,149 = 0.1, p = 0.88

   Attention problems

70.3 (11.3)

70.5 (9.9)

68.3 (9.6)

F_2,149 = 0.6, p = 0.56

   Externalizing problems

69.3 (9.5)

69.2 (11.4)

72.8 (7.6)

F_2,149 = 1.6, p = 0.21

   Aggressive behavior

71.4 (11.9)

72.9 (13.6)

75.1 (9.7)

F_2,149 = 0.8, p = 0.46

Diagnosis C/I/H

21/16/5

42/30/9

25/5/4

χ² = 6.6, df = 4, p = 0.15

Comorbidity (%) with

   CD

28.5%

28.5%

30.5%

χ² = 0.03, df = 2, p = 1.0

   ODD

38.0%

37.5%

42.5%

χ² = 0.2, df = 2, p = 0.88

   AD

44.5%

28.0%

19.0%

χ² = 5.4, df = 2, p = 0.07

   MD

16.7%

13.3%

3.8%

χ² = 2.4, df = 2, p = 0.30

Previously medicated (%)

51.3%

46.7%

48.4%

χ² = 0.22, df = 2, p = 0.90