Genetic epidemiology of irritable bowel syndrome

Table 1 Familial aggregation studies

Authors (Year)	Number of IBS patients	Conclusion
Whorwell et al[3] (1986)	100	Significant number of IBS patient had another family member with IBS
Levy et al[4] (2000)	373	Children of parents with IBS made more visits for gastrointestinal symptoms
Locke et al[5] (2000)	643	People with functional gastrointestinal disorders had higher odds of reporting a relative with similar symptoms
Kalantar et al[6] (2003)	181	IBS prevalence was higher among IBS patients' relatives
Saito et al[7] (2008)	50	Statistically higher percentage of IBS patients’ relatives had IBS
Saito et al[8] (2010)	477	50% of IBS patients had at least another relative with IBS
Waehrens et al[9] (2015)	51952	Increased risk of IBS among first, second and third degree relatives of IBS patients

IBS: Irritable bowel syndrome.

Table 2 Candidate genes associated with irritable bowel syndrome

Gene studied	Polymorphism
Serotonin or 5-HT reuptake transporter (SERT) gene –SLC6A4	5-HTT LPR – S and L alleles[23]
	rs25531 – A and G alleles[34]
	VNTR - alleles with 9, 10, 11 and 12 repeats[24]
5HT2A	1438 (G/A) and 102 (C/T)[41]
5HT3A	c.-42C>T[85]
5HT3E	rs62625044 - 76 (G/A)[44]
Tryptophan hydroxylase 1 (TPH1)	rs4537731 – 6526 (A/G)[45]
	rs684302
	rs21105
	rs1800532 – 218 (A/C)
	rs1799913 – 779 (A/C)
Tryptophan hydroxylase 2 (TPH2)	rs4570625 – 709 (G/T)[45]
Tumor necrosis factor–alpha (TNF-α)	308 (G/A)[53]
Transforming growth factor beta 1 (TGF-β1)	869 (T/C)[54]
	915 (G/C)[54]
Interleukin-10 (IL-10)	rs1800870 - 1082 (G/A)[50]
	rs1800871 - 819 (C/T)[53]
	rs1800872 - 592 (A/C)[56]
Cannabinoid receptor 1 (CB1)	AAT triplets[59]
	rs324420[60]
	rs806378[61]
Tumor necrosis factor super family 15 (TNFSF15)	rs4263839[62]
Cholecystokinin 1(CCK1)	779 (T/C)[64]
Catechol-o-methyltransferase (COMT)	rs 4680 - 158 (Val/Met)[68]
Guanine nucleotide binding protein (GNβ3)	rs 5443 - 825 (C/T)[68]
Corticotropin releasing hormone receptor 1(CRH1)	rs110402[75]
	rs242924
	rs7209436
α2-adrenergic receptor 2A	1291 (C/G)[80]
α2-adrenergic receptor 2C	Del 322-325[78]
Cholinergic muscarinic receptor type 3	rs3738435[82]