1. 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, SNP
4q27 SNP rs :
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: Intermediate risk: High risk for:
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. What changes?
Romanos. Gastroenterology. 09

28. Conclusive remarks HLA: Non-HLA genotypes:
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!