Since both the DRD2 TaqIB and TaqIA SNPs were associated with BPD traits, haplotype analyses were conducted using the Unphased program. Again, only the US young adult sample analysis yielded significant results (likelihood ratio χ2 = 12.49, df = 2, p = 0.002), with the B1 ~ A1 (A ~ T) haplotype conferring risk for BPD traits: OR = 4.89 (2.05 - 11.66). Furthermore, the haplotype constructed from the three DRD2 SNPs was also significantly associated with BPD traits: likelihood ratio χ2 = 13.91, df = 4, p = 0.008, OR = 7.35 (2.38 - 22.7) for the A ~ C ~ T haplotype. The estimated haplotype analyses for the DRD4 -616 C and -521 T alleles showed association with BPD traits in both samples: US young adult sample: likelihood ratio χ2 = 10.41, df = 3, p = 0.015; Hungarian patient sample: likelihood ratio χ2 = 9.81, df = 3, p = 0.02. In addition, the exact chromosomal localization of the two DRD4 SNPs could be determined by direct haplotyping methods [46]. Genetic association analyses were conducted using the
