Table 5. Effect of SNP4 genotype on NAA levels in left (L) and right (R) dorsolateral prefrontal cortex (DLPFC).

	NAA
SNP4 genotype	L DLPFC	R DLPFC	Valid number
Index A/A	2.34 (0.34)	2.39 (0.33)	49
Index A/G	2.44 (0.38)	2.35 (0.39)	47
Index G/G	2.58 (0.50)	2.68 (0.4.4)	8
sib A/A	2.40 (0.31)	2.40 (0.35)	50
sib A/G	2.40 (0.45)	2.45 (0.38)	40
sib G/G	2.42 (0.47)	2.37 (0.40)	12
Controls A/A	2.30 (0.26)	2.22 (0.26)	23
Controls A/G	2.47 (0.43)	2.42 (0.37)	18
Controls G/G	2.99 (0.60)	2.73 (0.11)	3
All groups	2.40 (0.38)	2.39 (0.36)	250

Subjects with an A allele have lower levels than G/G homozygotes. Although we did not see a significant group by genotype interaction, genotype seemed to have little effect in the sibling group. SDs are given in parentheses. Genotype groups were well matched for age, gender, IQ, and education.