Coeliac disease

1. Coeliac disease Can genotyping help to diagnose coeliac disease?

2. Difficult diagnosis • Asymptomatic patients: relatives • Moderate histological lesions (Marsh 1-2) • Positive Ab without histological lesion: not perfectly specific • Gluten free diet before intestinal biopsy • Usefulness of HLA genotyping?

3. Genetic origins • Ethnic differences in disease incidence/prevalence • Familial aggregation: • 5–15% first-degree relatives • 30% HLA identical sibs • Monozygotic twins 83–86% • Dizygotic twins 11% Greco. Gut. 02 Sollid. J Exp Med 89

4. Genes involvement • Susceptibility loci: chromosomes 2, 5, 6, 9, 15, 19 • Genetic association studies of functional candidate genes: • CTLA4 • MYO1XB • Association with genetic syndromes: • Down syndrome • Turner syndrome • Williams syndrome

5. MHC Class II Wolters. Am J Gastroenterol. 08

6. HLA • Major histocompatibility complex (MHC): 6p21 • MHC class II : • Loci HLA-DQ, HLA-DP and HLA-DR, • Expressed on professional antigen presenting cells • HLA-DQ2: • Alleles DQA1*0501 and DQB1*0201 • DQ2 (DR3 or DR5/7): 90-95% of CD patients vs 15-20% of controls • 3% of HLA-DQ2 positive population will develop a CD • Risk effect: 38-53% • DQ8: • 5-10% of CD patients vs 20% of controls Sollid. J Exp Med. 89 Petronzelli. Ann Hum Genet. 97

7. HLA-DQ2 alleles: a gene dosage effect • Highest risk if: • 2 alleles (DQA1*0501 and DQB1*0201) • In cis or in trans • Further increased if: • Homozygous for the DQ2.5cis • A second DQB1*02 on the 2nd chromosome Vader. Proc Natl Acad Sci USA. 03

8. Sollid. Nat Rev Immunol. 02

9. HLA DQ2/DQ8 are more frequent in female • Female: 94% vs 85% in males (P = 1.6 × 10−3) • NPV: 99.1% in female and 90.5% in males • Majority of the DQ2/DQ8 negative cases were male • DQ2/DQ8 transmission is more frequent from fathers to daughters (P = 0.02): • 61% of female patients • 42% of male patients Megiorni. Am J Gastroenterol. 08

10. HLA: an excellent NPV Kaukinen. AM J Gastroenterol. 02

11. HLA genotyping in practice Kaukinen. AM J Gastroenterol. 02

12. Kaukinen. AM J Gastroenterol. 02

13. When diagnosis still remains uncertain • Borderline small bowel mucosal finding • Positive serology without villous atrophy • Gluten-free diet before biopsy

14. Familial screening Srivastava. J Gastroenterol Hepatol. 10

15. first-degree relatives • 2.8-12% CD prevalence in relatives • 5.8% to 14% of serology positive relatives • Higher prevalence in siblings vs parents? • 59%-85% HLA DQ2/DQ3 DQ2-positive relatives • 14.3% HLA negative relatives Srivastava. J Gastroenterol Hepatol. 10 Bonamico. JPGN. 06

16. Cost/effectiveness Srivastava. J Gastroenterol Hepatol. 10

17. tTG + Total IgA NEGATIVE: 2 years later HLA genotyping tTG screening POSITIVE : Intestinal biopsy Ab POSITIVE Ab NEGATIVE HLA + Serologic follow-up HLA - Clinical follow-up Bonamico. JPGN. 06

18. HLA genotyping • Non specific: only NPV • Long-life information • Diagnosis remained uncertain: • Borderline intestinal lesions, • Positive serological diagnosis without villous atrophy • If gluten free diet: • Surveillance for HLA positive cases • Role of: • Positive EmA? • Increased g/d IELs?

19. First coeliac disease GWAS • 778 patients, 1422 controls, 310 605 SNP • 4q27 SNP rs13119723: • English, dutch and irish populations: p=2x10-7 • Meta-analysis: p=4.8x10-11 • Replication in UK and scandinavian populations Van Heel. Nat Genet. 07

20. First coeliac disease GWAS • Several genes in high level of linkage disequilibrium: • KIAA1109: unknown function • Adenosine deaminase domain containing 1 (ADAD1) • Interleukin2 (IL2): T cell activation and proliferation • IL21: B, T and NK cells proliferation and IFNg production • Also linked to type 1 diabetes and rheumatoid arthritis Van Heel. Nat Genet. 07

21. Follow-up of Coeliac GWAS • Genotyping of 1020 non-HLA SNP • In Dutch, Irish and UK collections • Meta-analysis of 2410 cases vs 4828 controls • 7 new significant regions Hunt. Nat Genet. 08

22. Regions of the coeliac GWAS • In 5’ region of regulator of G protein signalling 1 (RGS1): • Regulation of G protein signalling activity • 3p21: CCR3 and CCR5 • 3q25–2: IL12A cytokine subunit • 6q25: TAGAP: a T cell activation GTPase activating protein • 3q28: Lim domain containing preferred translocation partner in lipoma (LPP): not immune? • 2q11–12: IL1RL1, IL18R1, IL18RAP and solute carrier SLC9A4 • 12q23: SH2B3 • TNFAIP3 • REL Hunt. Nat Genet. 08 Trynka. Gut. 09

23. Non-HLA genes: a new diagnostic tool? Romanos. Gastroenterology. 09

24. 3 risk groups • Low risk: • HLA-DQ2 negative (DQ2.5 and DQ2.2) • Intermediate risk: • Homozygous for HLA-DQ2.2 • Heterozygous for HLA-DQ2.5 • Heterozygous for HLA-DQ2.2 • High risk for: • Homozygous for HLA-DQ2.5 • Composite heterozygote HLA-DQ2.5/DQ2.2

25. The tested SNPs Romanos. Gastroenterology. 09

26. Non HLA genes increase CD risk 7.5% of HLA DQ2 positive cases are reclassified if ≥ 13 non HLA alleles Sensitivity increases from 46.6 to 49.5% Specificity decreases from 93.6% to 92.8% Romanos. Gastroenterology. 09

27. Romanos. Gastroenterology. 09 What changes?

28. Conclusive remarks • HLA: • Good NPV, especially in female • Long-life information • Can avoid repeted exams in: • Asymptomatic DQ2/DQ8 negative cases (screening) • Serology negative patients with atypical symptoms • Cost/effectiveness? • Non-HLA genotypes: • Slight increasing of diagnostic effectiveness • Will evoluate with new susceptibility SNPs • Cost as to be evaluated!