Table 1.

Association between clinical characteristics and genotypes of rs2530223

	AA	GA/GG	Statistics	p value	Eta squared
Women/men	5/0	12/6		0.27
Age (years)	42.2 ± 10.9	43.1 ± 9.5	0.18	0.5
MOH duration	3.9 ± 3.8	5.4 ± 3.6	0.81	0.37
Number of headache days/month	18.6 ± 1.8	21.9 ± 4.1	3.04	0.09	0.12
Headache intensity	2.0 ± 0.7	2.2 ± 0.6	0.44	0.51	0.02
Number of drugs/month abused	14.2 ± 4.1	23.8 ± 6.7	9.47	0.006	0.30
Days/month of drug abuse	11.4 ± 2.6	19.0 ± 5.3	9.06	0.007	0.31
VPA responders/nonresponders	4/1	9/9	–	0.33

Continuous data are expressed in mean ± standard deviation; dichotomous data are expressed as frequencies

Headache intensity was measured with a 4-point scale with 0 = no pain, 1 = mild headache, 2 = moderate headache, 3 = severe headache. Headache attacks and drugs used during the baseline period were collected using a headache diary. Additional information on how these variables were collected is available in Sarchielli et al., 2014 [22]. Significant variables are indicated in bold

MOH medication overuse headache, VPA sodium valproate