Coeliac disease
Can genotyping help
to diagnose coeliac disease?
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?
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
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
MHC Class II
Wolters. Am J Gastroenterol. 08
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
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
Sollid. Nat Rev Immunol. 02
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
HLA: an excellent NPV
Kaukinen. AM J Gastroenterol. 02
HLA genotyping in practice
Kaukinen. AM J Gastroenterol. 02
Kaukinen. AM J Gastroenterol. 02
When diagnosis still
remains uncertain
• Borderline small bowel mucosal finding
• Positive serology without villous atrophy
• Gluten-free diet before biopsy
Familial screening
Srivastava. J Gastroenterol Hepatol. 10
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
Cost/effectiveness
Srivastava. J Gastroenterol Hepatol. 10
tTG + Total IgA
POSITIVE :
Intestinal biopsy
NEGATIVE: 2 years later
HLA genotyping
Ab POSITIVE
tTG screening
Ab NEGATIVE
HLA +
HLA -
Serologic follow-up
Clinical follow-up
Bonamico. JPGN. 06
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?
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
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
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
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
Non-HLA genes:
a new diagnostic tool?
Romanos. Gastroenterology. 09
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
The tested SNPs
Romanos. Gastroenterology. 09
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
What changes?
Romanos. Gastroenterology. 09
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!