Within the IBS patient group, those who were homozygous for the major allele of the ADRA1D SNP rs1556832 had higher IBS symptom severity (i.e. overall severity, abdominal pain, bloating, and usual severity) compared to those who were heterozygous or homozygous for the minor allele after adjusting for race and sex (p = 0.010). The gene discussed is ADRA1D; the disease is irritable bowel syndrome.