Table 4.

Comparison of genotypes of significant result from the interaction analyses of previously implicated SNPs with a cumulative pre- and perinatal adversity score in relation to lifetime tic severity

SNP	Genotype	N	Initial sample						Replication sample
			Lifetime tic severity Mean (SD) a	Cumulative pre- and perinatal adversity score Mean (SD) b	β	Standard error	T	P c, d (Genotype)	N	β	Standard error	T	P c, d (Genotype)
rs6539267	TT	250	15.3 (8.20)	3.30 (3.32)	–				352
	CT	224	15.7 (7.80)	3.77 (3.76)	0.039	0.21	− 1.87	0.06	344	0.74	0.61	1.20	0.23
	CC	40	15.2 (9.62)	3.9 (3.75)	1.12	0.42	2.62	0.009	82	− 0.03	1.00	− 0.03	0.98

SNP single-nucleotide polymorphism

^aLifetime worst-ever tic severity was assessed based on a modified version of the Yale Global Tic Severity Scale (Dietrich et al. 2015)

^bCumulative pre- and perinatal adversity score (previously described in Abdulkadir et al. 2016) was constructed from addition of 38 possible adverse events as measured by the self-report or parent-on-child report version of the Modified Schedule for Risk and Protective Factors Early in Development questionnaire (Walkup and Leckman 1988)

^cAnalyses were corrected for age, sex, and socioeconomic status

^dMajor allele homozygous genotype was used as the reference genotype