Interaction between catechol-O-methyltransferase Val/Met polymorphism and cognitive reserve for negative symptoms in schizophrenia

Table 1 Demographics, clinical symptoms and intelligence quotient in catechol-O-methyltransferase Met-carriers and Val homozygotes

	Met-carriers, n = 27			Val homozygotes, n = 27			Statistic	u value	P value
	Mean	SD		Mean		SD
Age	34.59	7.66		33.15		7.23	t = 0.713	52	0.479
Educational level	14.37	3.52		14.98		3.90	t = -0.604	52	0.548
Female/male	16/11			14/13			χ² = 0.300	1	0.584
Han nationality/non	24/3			25/2			NA	NA	1.000
Employment/non	8/19			15/12			χ² = 3.711	1	0.054
Marriage/non	12/15			10/17			χ² = 0.307	1	0.580
Current smoker/non	3/24			3/24			NA	NA	1.000
Clozapine user/non	5/22			4/23			NA	NA	1.000
Chlorpromazine equivalents	474.96		258.23	426.50	323.60		t = 0.608	52	0.546
Duration of illness	11.73		8.56	11.24	7.51		t = 0.223	52	0.825
PANSS positive	9.48		3.89	8.56	2.90		t = 0.992	52	0.326
PANSS negative	11.15		3.31	13.59	4.93		t = -2.138	52	0.037
PANSS general	21.48		5.15	20.59	3.86		t = 0.718	52	0.476
PANSS total	42.11		10.02	42.74	7.89		t = -0.257	52	0.799
WAIS-RC information	20.67		4.66	18.41	4.80		t = 1.756	52	0.085
WAIS-RC similarities	18.67		2.27	18.33	2.76		t = 0.485	52	0.630
WAIS-RC picture completion	11.41		3.12	10.15	2.80		t = 1.563	52	0.124
WAIS-RC block design	36.19		7.19	36.44	8.44		t = -0.122	52	0.904
WAIS-RC total	106.61		9.75	103.00	10.54		t = 1.306	52	0.197

COMT: Catechol-O-methyltransferase; PANSS: Positive and negative syndrome scale; WAIS-RC: Chinese version of the Wechsler adult intelligence scale.