Genetic contribution of the HLA region to the familial clustering of coeliac disease

Ann. Hum. Genet. (1997), 61, 307–317

Printed in Great Britain

307

Genetic contribution of the HLA region to the familial clustering

of coeliac disease

F. PETRONZELLI", M. BONAMICO#, P. FERRANTE", R. GRILLO", B. MORA",

P. MARIANI#, I. APOLLONIO", G. GEMME$ M. C. MAZZILLI"

"Dipartimento di Medicina Sperimentale, Universita[ ‘La Sapienza’, Viale Regina Elena,

324–00161 Roma, Italy#Dipartimento di Pediatria, Universita[ ‘La Sapienza’, Roma, Italy

$ Istituto Gaslini, Universita[ di Genova, Italy

(Received 22.12.95. Accepted 14.4.97)

In order to assess the effect of the HLA region on familiality of coeliac disease (CD), we carried out

a study on 121 CD index cases and 325 first degree relatives. The transmission disequilibrium test

confirmed the importance of the HLA-DR3 haplotype in CD susceptibility. However, the different

distortion found in affected children inheriting maternal or paternal DR3 alleles suggested that the

sex of the parent might influence the risk conferred by this haplotype. The increase in risk to siblings

of affected individuals relative to the risk in the general population (λs) and the contribution of the

HLA genes to this clustering (λsHLA

) have also been estimated. Non-overlapping data from the

literature have been collected and combined with our sample to extend such analysis. Then, the

percentage contribution of the HLA region to the development of CD among siblings was 36±2%.

This result confirms that the HLA genotypes are an important genetic background to CD

development but shows that additional susceptibility factors remain to be identified.

Coeliac disease (CD), also known as gluten

sensitive enteropathy (GSE), is a condition in

which the immune response to ingested gluten is

accompanied by intestinal mucosal damage

(Trier, 1991). The resulting atrophy of the villi of

the proximal small intestine leads to mal-

absorption of nutrients and the clinical features

of CD. The symptoms and the epithelial damage

are reversed by the exclusion of gluten from the

diet. The pathogenesis of CD is believed to

involve interaction between genetic and environ-

mental factors (Polanco, 1981).

The reported prevalence of clinically manifest

CD is around 1:1000. However, because of the

increasing recognition of subclinical or silent

cases, the true prevalence is much higher than

supposed, and it probably approaches 1:300

(Catassi et al. 1994; Troncone et al. 1992). The

familial clustering of the disease is documented

by the increased prevalence in relatives; in a

multicentred study, undertaken to investigate

the prevalence of CD among first-degree relatives

of patients, an estimated risk of 8±7% was found

(Auricchio et al. 1988). The genetic contribution

to this increased risk is supported by the high

rate of concordance for disease (71%) among

monozygotic twins (Polanco et al. 1981).

Among sib pairs in which both siblings are

affected with CD, the HLA haplotype sharing is

significantly more than expected as reviewed by

Scholz & Albert (1983). Furthermore, several

studies have reported that CD more frequently

occurs in HLA-DR3, DQ2 positive subjects.

Indeed, a significant part of the genetic sus-

ceptibility to CD seems associated with products

of the major histocompatibility complex (MHC)

308 F. P

encoded within the class II region (Sollid &

Thorsby, 1993).

Genes in the class II region are clustered into

three major subregions named HLA-DP, -DQ

and -DR. Each class II molecule on the cell

surface occurs as a heterodimer consisting of an

α chain encoded by an A gene and a β chain

encoded by a B gene. A hallmark of the HLA

gene complex is linkage disequilibrium between

alleles at different loci, which greatly complicates

any attempt to pinpoint disease susceptibility to

a specific locus. In this regard, the HLA typing of

patients and controls from different populations

could be of great relevance. Concerning CD,

Spanish (Mearin et al. 1983) and Italian studies

(Trabace et al. 1984; Morellini et al. 1988)

revealed a lower association of the disease to the

DR3 haplotype than reported in the North

Europe populations while a new association to

DR5,7 heterozygous combination was found.

This observation led to the exclusion of a direct

involvement of the DR3 molecule in the patho-

genesis of CD. More recently, different studies

(Morellini et al. 1986; Sollid et al. 1989; Hall et al.

1992) have provided evidence for a primary HLA

association of CD to the DQ(α1*0501, β1*0201)

heterodimer, encoded in cis on the DR3 haplo-

type or in trans in the DR5,7 heterozygous

individuals. The immunopathogenic importance

of this association is supported by the finding

that, in the small intestine, the CD-associated

DQ heterodimer represents the main gluten-

presenting molecule (Lundin et al. 1990).

In a group of Italian paediatric patients we

have reported (Mazzilli et al. 1992) that 92% of

CD patients (50% DR3 and 42% DR5,7) carried

the high-risk DQα}β dimer. In accordance with

previous studies (Tosi et al. 1986), most of the

dimer negative patients typed as DR4,DQ8. A

few DR3 and DR5,7 negative cases were also

described (Grillo et al. 1996).

The aim of the present study was to evaluate

the risk of coeliac disease among first-degree

relatives of affected children in relation to the

presence of susceptible HLA molecules. The data

presented here are discussed together with those

reported in the literature in an attempt to

contribute in defining the relative role of the

HLA region and other genes in the familial

clustering of the disease.

Families

The whole sample consisted of 447 subjects :

121 unrelated children with coeliac disease and

325 first-degree relatives (212 parents, 113 sib-

lings) and one twin. Altogether, 144 patients

were observed (121 index cases, 18 siblings and 5

parents). In the 18 families with 2 affected

siblings we considered as ‘ index case’ the first

being diagnosed. The diagnosis remained un-

certain in 2 parents and 4 siblings. The twin pair

included two HLA identical affected males but

not enough data were available to conclude if

they were monozygous.

The composition of the families is reported in

Table 1. HLA typing was performed in 153

parents, 79 siblings and one twin of 81 index

cases. In total, 95 index cases were HLA typed

including 28 from earlier studies (Ferrante et al.

1992; Mazzilli et al. 1992). The numbers of typed

subjects in the different groups are indicated in

brackets in the table. In order to complete the

HLA haplotypic segregation the typing was

carried out in twelve more parents but they were

not considered in any of the analyses reported in

the following paragraphs because of lack of

clinical information.

Diagnosis

The diagnosis of CD was based on small

intestinal biopsies, according to the new Euro-

pean Society for Paediatric Gastroenterology

and Nutrition (ESPGAN) criteria (Walker-Smith

et al. 1990). While all the index cases were

biopsied, as far as the relatives are concerned

only ‘suspected’ cases were requested to undergo

the biopsies. The suspicion of CD was based on

clinical examination and on the presence of

antigliadin (AGA), IgA and IgG, and}or anti-

HLA and familial clustering of CD 309

Table 1. Families examined

Indexcases

Parents Siblings Twin

n CD® CD CD? CD® CD CD? CD

23 241 2 18 2 21 2 39 2 11 2 14 2 1 13 2 2 11 2 11 2 1 12 1 12 1 11 1 1 11 1 1 11 1 1 1 17 17 1 11 1 11 1 33 11 22 1

121 205 5 2 91 18 4 1(95)b (149) (2) (2) (57) (18) (4) (1)

121 212 113 1 Total 447(95) (153) (79) (1) (328)

a CD®, unaffected; CD, affected; CD?, unknown.b Parentheses indicate numbers of HLA typed subjects.

endomysium (AEA) antibodies. A more detailed

clinical description of the cases is reported

elsewhere (Bonamico et al. 1996).

HLA typing

The index cases and their relatives were typed

for the HLA-DRB1, -DQA1 and -DQB1 genes

using PCR and sequence-specific oligonucleotide

probing (SSOP) following standard methods

(Kimura & Sasazuki, 1992). The primers used

were identical to DRBAMP-AN, DRBAMP-B;

DQAAMP-A, DQAAMP-B; DQBAMP-A and

DQBAMP-B distributed during the 11th In-

ternational Histocompatibility Workshop. The

oligoprobes were selected from the Workshop

reagents to match sequence variations of 12

DRB1, 5 DQA1 and 10 DQB1 alleles.

Statistical analysis

The distortion of haplotype sharing in sibpairs

was tested by the χ# statistic ‘Y’ of Blackwelder

and Elston (1985) as follows:

χ#‘Y ’¯4[(r

#®n}4)#1}2(r

"®n}2)#(r

!®n}4)#]}n.

(1)

The Transmission test for Linkage Disequi-

librium (TDT) (Spielman et al. 1993) was used to

analyse the DR3 allele segregation. The TDT is a

nonparametric method based on the analysis of

the transmission of a disease-associated marker

allele from a heterozygous parent to both affected

and unaffected offsprings. The χ# test takes the

form of:

χ#¯ (b®c)#}bc, (2)

310 F. P

where b is the number of transmitted alleles and c

the number of transmissions of other alleles.

The λsparameter (Risch, 1987) has been used

to define the relationship between the risk in

siblings (Ks) and the population prevalence (K)

as follows:

λs¯K

s}K. (3)

The contribution of the HLA region (λsHLA

) has

been estimated from the expected proportion of

affected sib pairs sharing zero haplotypes identi-

cal-by-descent (IBD) (0±25) divided by the ob-

served proportion.

Assuming a multiplicative model as suggested

by Risch (1987), the HLA contribution to the λs

can be expressed as percentage by the following

formula:

% λsHLA

¯ 100(log λsHLA

}log λs). (4)

Nomenclature

The latest recommendation from the WHO

HLA Nomenclature Committee was used

(Bodmer et al. 1995).

1. Prevalence of CD in first degree relatives

On the basis of clinical symptoms and presence

of antigliadin (IgA and IgG) and}or anti-

endomysium antibodies, a diagnosis of suspected

CD was made for 17}212 parents (8±0%), 25}113

siblings (22±1%) and for the twin. All the cases

identified by the first screening were asked to

undergo the biopsy}ies. Five parents, 18 siblings

and the twin were found to be affected on the

basis of intestinal mucosa atrophy. Two parents

and 4 siblings have not completed the diagnostic

procedures yet or refused to undergo the biopsy;

they have been classified as unknown and not

considered in the analysis reported in the fol-

lowing paragraphs. Thus the prevalence of the

disease in the parents of affected children was

2±4% (5}212) if only the biopsied cases were

considered or 3±3% (7}212) taking into account

also the unknown subjects (Table 2). Similarly,

the prevalence in the siblings of the index cases

was evaluated in a range from 15±9% to 19±5%.

Using the chi-square test of a 2¬2 contingency

table, there was a significant difference between

the two groups even comparing the two closest

values (p! 10−%).

2. HLA haplotype sharing in sib pairs

The sharing of HLA haplotypes IBD has been

analysed in the sib pairs collected in the present

study together with those available from the

literature (Table 3). The frequencies of sharing

two, one or zero HLA haplotypes in affected

siblings were obviously distorted in our sample

as well as in the combined data, as shown by the

χ# ‘Y’ test statistic. Taken together, the results

on 158 affected sib pairs gave frequencies of

50±6%, 42±4% and 7±0% for sharing 2,1 and 0

HLA haplotypes respectively. On the other hand,

non-affected siblings did not differ significantly

from the expected proportion, both in our sample

(22±8%, 56±1%, 21±1%) and in the combined one

(21±4%, 51±1%, 27±5%).

In Table 4 is reported some information

concerning the 18 CD sib pairs of the present

study together with the 4 cases with ‘unknown’

siblings and the pair of twins. Regarding the

clinical presentation of the disease, all the index

cases showed a manifest form, typical or atypical,

while most siblings were clinically silent. All

dimer negative index cases and affected siblings

typed as DR4. Three out of 4 siblings classified as

CD ‘unknown’ showed HLA typing at risk of

CD. The twins were both DR5}7 positive.

3. Recurrence of CD in relatives and HLA typing

Seventy-five siblings and 151 parents were

HLA typed, including all the 18 siblings and only

2 of the five parents identified as affected. The

subjects carrying the DQ(α1*0501, β1*0201)

dimer and}or DR4 molecule were classified as

‘high risk’, while the absence of these antigens

characterised the ‘ low risk’ group (Table 5).


Table 2. Prevalence of CD in relatives of affected children

BiopsyPrevalence

n Suspected Pos Neg ..a (%)

Parents 212 17 (8±0%) 5 10 2 2±4–3±3p! 10−%

Siblings 113 25 (22±1%) 18 3 4 15±9–19±5a .., not done.

Table 3. 2,1,0 identical HLA haplotypes in affected siblings

Shared HLA haplotypes

2 1 0 χ#Y p

Present study 10 6 2 9±11 *a

Falchuk et al. (1972) 1 3 —Asquit et al. (1974) 3 — —Makintosh et al. (1978) 8 6 —Rosekrans et al. (1978) 2 3 —Betuel et al. (1980) 7 5 1Polanco et al. (1981) 3 2 —Orgad et al. (1981) 2 1 1McKenna et al. (1983) 8 5 1Mearin et al. (1983) 2 1 —Sholtz & Albert (1983) 16 10 2Mearin et al. (1985) — 1 —Caffrey et al. (1990) 4 4 2Bolsover et al. (1991) 4 4 —Hernandez et al. (1991) 10 16 2

Combined data 80 67 11 63±9 ***(50±6%) (42±4%) (7±0%)

a ..¯ 2.

Out of the 75 siblings, 59 (78±7%) were ‘high

risk’, 48 (64±0%) being dimer positive, 10

(13±3%) DR4 positive and one presenting both

dimer and DR4 molecules. Eighteen out of the 59

‘high risk’ (30±5%) and none of the 16 ‘ low risk’

sibs was affected. On the other hand, out of the

151 HLA typed parents 89 (58±9%) were ‘high

risk’ subjects and two of them were affected

(2±2%). Of the remaining 62 carrying ‘ low risk’

HLA molecules none was affected.

A significant difference was detected between

the ‘high risk’ siblings and parents (78±7% v.

58±9%, p¯ 2¬10−$) presumably due to the

possible trans arrangement of HLA suscepti-

bility alleles. However, the number of subjects

that developed CD among those carrying sus-

ceptibility HLA molecules was much higher

among siblings than parents (30±5% v. 2±2%,

p¯ 9¬10−().

4. F:M ratio

As shown in Table 6, the F:M ratio in the

affected subjects, including index cases, siblings

and parents, was 2±1:1 while in unaffected

subjects it was approximately 1:1 as expected.

All the 5 affected parents were mothers. Affected

sib pairs (see Table 4) consisted of 25 females and

11 males distributed in 8 FF, 6 FM, 3 MF and 1

MM pairs. The F}M ratio in affected siblings was

lower (11:7¯ 1, 57) than that of index cases

(14:4¯ 3, 5), thus confirming the known charac-

teristic of multifactorial threshold traits

(Ottman, 1987).

5. Transmission of DR3 haplotype from

heterozygous parents to affected and unaffected

children

The TDT was used in order to examine the

312 F. P

Table 4. Affected sib-pairs

Index cases Affected siblings

HLA HLAClinical Birth Clinical Shared

Sex form order DR Dimer Sex form Age DR Dimer haplotypes

CO F Atypical 1 1,3 D M Silent 9 1,3 D 2CI F Typical 2 3,7 D F Silent 11 3,7 D 2MA F Typical 2 3,7 D M Silent 5 3,7 D 2PA M Typical 1 3,7 D M Silent 2 3,7 D 2PO F Atypical 2 3,7 D M Atypical 12 3,7 D 2PI M Typical 2 3,13 D F Silent 12 3,5 D 1GI F Typical 2 3,13 D M Silent 2 3,14 D 1TY F Typical 2 3,16 D F Silent 9 3,3 D 1AN F Typical 2 5,7 D M Silent 22 5,7 D 2BE F Typical 1 5,7 D F Atypical 5 5,7 D 2LU F Typical 2 5,7 D F Silent 15 5,7 D 2MU M Atypical 1 4,5 D® F Silent 22 4,5 D® 2NE F Typical 2 4,5 D® F Silent 19 4,5 D® 2GR F Atypical 2 3,7 D F Silent 22 4,7 D® 1MA F Typical 1 1,3 D M Silent 4 4,10 D® 0DA F Typical 1 3,5 D F Silent 2 5,7 D 0FR M Typical 2 5,7 D F Silent 12 3,7 D 1OR F Typical 2 4,9 D® F Typical 4 5,9 D 1SC F Typical 1 3,15 D M Unknown 10 3,5 D 1CO F Typical 2 4,7 D® F Unknown 3 5,7 D 1BA F Typical 1 5,7 D F Unknown 9 3,5 D 1LV M Atypical 2 13,14 D M Unknown 14 13,16 D® 0

Twins:PA M Typical 5,7 D M Silent 11m 5,7 D 2

Table 5. Susceptible HLA molecules and development of CD in siblings and parents

HLA Siblings n¯ 75 Parents n¯ 151

‘high risk’ Total CD Total CD

DIM}DR4} 1 0 7 0}® 48 14 72 2®} 10 4 10 0

59 (78±7%) 18 (30±5%) 89 (58±9%) 2 (2±2%)

‘ low risk’DIM}DR4

®}® 16 0 62 0

Table 6. F:M ratio

Affected Unaffected

F M F M

Index cases 82 39Siblings 11 7 45 46Parents 5 0 107 98

98 46 152 1442±1:1 1±05:1

transmission of the DR3,DQA1*0501,DQB1*-

0201 haplotype (no recombinants were found).

The analysis was initially carried out in our

sample and subsequently extended to 40 Spanish

families where all members were previously HLA

typed (Polanco et al. 1981 and Mearin, personal

communication). The CD diagnosis in these

families was made according to ESPGAN criteria

(Meeuwisse, 1970).

In order to evaluate the sex influence on the

segregation of this susceptible haplotype within


Table 7. Transmission Disequilibrium Test(TDT) of DR3 haplotype

Present study Combined data

Affected Unaffected Affected Unaffected

DR3 heterozygousA. Mothers

3m — χ#TDT

3m — 3m — χ#TDT

3m —

Daughters 19 4 9±8** 3 4 30 6 16±0*** 12 14Sons 8 1 5±4* 11 4 18 1 15±2*** 17 10

Total 27 5 15±1*** 14 8 48 7 30±6*** 29 24

B. Fathers 3p — χ#TDT

3p — 3p — χ#TDT

3p —Daughters 27 1 24±1*** 5 2 34 5 21±6*** 8 8Sons 9 6 0±6 .. 10 7 13 9 0±7 .. 15 13

Total 36 7 19±5*** 15 9 47 14 17±8*** 23 21

the disease, maternal and paternal transmission

and F and M children were separately considered.

Table 7 shows the transmission of DR3 haplotype

from heterozygous mothers (A) and heterozygous

fathers (B) to affected and unaffected offsprings.

When daughters and sons were considered to-

gether, both maternal and paternal DR3 trans-

mission was significantly distorted in affected

but not in unaffected children. However, a first

analysis carried out on our families showed that

paternal DR3 haplotype was transmitted signi-

ficantly more than expected to CD daughters

(χ#TDT

¯ 24±1) but not to CD sons (χ#TDT

¯ 0±6).

The 2¬2 tables gave a pFisher

¯ 0±0045. Extend-

ing such analysis to the combined sample, this

observation was confirmed; furthermore, the

comparison between maternal and paternal seg-

regation in affected sons became significant,

giving a pFisher

of 9¬10−$.

6. Genetic contribution of HLA region to the

familial clustering of CD

The degree of risk to siblings relative to the

risk in the general population can be measured

by the λs

parameter (Risch, 1987). A risk in

siblings of 0±159, from these data, and a preva-

lence in the general population of 0±0033 (Catassi

et al. 1994), provided a λsvalue for CD of 48±18.

Furthermore, the λs

for a particular locus or

region can be estimated from the expected

proportion of affected sib pairs sharing zero

alleles IBD divided by the observed proportion.

Since the sharing of zero HLA haplotypes IBD in

our 18 CD sib pairs was 0±11 (Table 3), the

resulting λs

for the HLA region was 2±27.

Assuming a multiplicative model (Risch, 1987),

it can be inferred that the HLA region con-

tributes 21±15% to the λs, as described in the

statistical analysis paragraph. In order to have a

more accurate estimate of the λs

parameter an

evaluation on data from the literature has been

done. The reports were selected on the basis of

Caucasoid origin, paediatric age of the index case

and rigorous immunological and}or bioptic cri-

teria for the diagnosis in the relatives (Mylotte et

al. 1974; Rolles et al. 1974; Shipman et al. 1975;

Ellis et al. 1981; Rolles et al. 1981; Stenhamar et

al. 1982; Auricchio et al. 1988). Cumulating these

data with those from the present study, the CD

prevalence in siblings became 0±11. Dividing this

value by the prevalence of the disease in the

European area (0±0033), the λswas estimated as

33±33. The sharing of zero haplotypes IBD on 158

sib pairs resulted in 7% as shown in Table 3,

therefore, the λsHLA

became 3±57 (36±2%).

Despite numerous population studies support-

ing the idea that the HLA region plays the main

role in the genetic susceptibility to many multi-

factorial autoimmune diseases, not enough fam-

ilial data are available to quantify the relative

contribution of HLA and other genes in the

development of these diseases. We presented

here a group of paediatric coeliac cases and their

relatives together with data from the literature,

314 F. P

with the double aim to contribute in evaluating

the prevalence of CD in relatives of affected

children and in assessing the HLA role on the

increased risks of disease in the siblings.

The screening procedure used in this study

consisted of two steps. All first-degree relatives

of the index cases were invited to take part in a

first level of study that included clinical and

immunological examinations and the ‘suspected’

subjects were asked to undergo biopsy}ies. The

diagnosis was confirmed in 86% of siblings and

33% of parents. This discrepancy could be

explained by the fact that with age AGA results

tend to become worse predictors of CD (Picarelli

et al. 1996). Furthermore, adults often manifest

clinical symptoms suggestive of CD which in fact

are due to different gastroenterological disorders.

Then the prevalence of CD in the 325 first-

degree relatives studied was 7% if only subjects

that had undergone biopsies were considered, or

8±9% including cases positive at the first screen-

ing but that have not concluded the diagnostic

iter, yet. This result is in agreement with those

previously reported in relatives of paediatric CD

patients where the average prevalence of 8±2%

can be calculated (Mylotte et al. 1974; Rolles et

al. 1974; Shipman et al. 1975; Ellis et al. 1981;

Rolles et al. 1981; Stenhamar et al. 1982;

Auricchio et al. 1988). Since the biopsy screening

procedure has been used in most of these cases,

our data attest the reliability of non-invasive

pre-screening protocol in detecting manifest as

well as subclinical cases, confirming previous

observations (Catassi et al. 1994).

When parents and siblings were separately

considered, the risks in the two groups were

significantly different, being in a range of 2±4–

3±3% and 15±9–19±5%, respectively. These re-

sults are in agreement with the suggested

approximate 5:1 ratio of children}adult patients

(Magazzu' et al. 1994). The prevalence of CD in

siblings here estimated is one of the higher

reported. However, we would like to emphasise

that most of them were asymptomatic.

The mode of inheritance of CD susceptibility

has not been established but it probably involves

several interacting loci. The association of CD

with the HLA region is the only consistently

observed genetic feature in this multifactorial

disorder. What is now largely accepted is the

direct role of the DQ(α1*0501, β1*0201) dimer in

the pathogenesis of the disease. The proposed

mechanisms may be the involvement in the

thymic selection of TCR repertoire and}or the

preferential binding and presentation of relevant

gliadin peptides. Although HLA typing is not

diagnostically significant, we propose it as a pre-

screening test in CD relatives to restrict the

number of subjects that must undergo further

investigations. Unlike the anti-gliadin and anti-

endomysium antibodies that occur when disease

occurs, the HLA alleles are predisposing factors

detectable at birth and therefore might have a

prospective value.

All affected relatives found in our sample

carried high risk HLA alleles, but in some familial

groups the disease was inherited with different

haplotypes. These families formally confirm that

HLA genes are not markers of a linked disease

gene but may themselves work as predisposing

factors. Really, the HLA susceptibility appears

primarily conferred by the concurrent presence

of DQA1*0501 and DQB1*0201 alleles, coding in

cis or in trans the DQα}β heterodimer. In the

majority of the patients a single copy of these

high risk alleles is sufficient for the development

of the disease (Petronzelli et al., 1993). This

observation leads us to consider the dominant

model as the most appropriate to explain the

HLA contribution to CD susceptibility. A gene

dosage effect of the DQB1*0201 allele in dimer

positive individuals has been recently reported

by Ploski et al. (1993). In our opinion, this result

is not in contrast with this model of inheritance

since a homozygosity influence on the patho-

logical phenotype has been observed for several

dominant genes. Furthermore, the high risk

conferred by the double dose of DQB1*0201

allele and the fact that in many families the

dimer is carried in trans could justify the

observed increase in frequency of sibling pairs

sharing two haplotypes that previously sug-

gested a recessive model of inheritance (Green-

berg et al. 1982).


Since DR3,DQA1*0501,DQB1*0201 is the

most frequent haplotype in CD patients, TDT

has been used to analyse its segregation in the

families. Looking at the whole affected progeny,

a high distortion of DR3 transmission from both

parents was found, as expected on the basis of

the strong association of DR3 with the disease.

However, the segregation from heterozygous

fathers became highly distorted in female but

not in male children. Our data combined with 40

Spanish families, that we regard as very similar

to our own sample, not only confirmed the trend

observed but also allowed the comparison of

DR3 maternal and paternal segregation in

affected sons. These data support the idea that

the sex of the parent transmitting the DR3

together with that of the child inheriting it may

influence the susceptibility conferred by this

haplotype. A similar model, even if in a single

gene disease, has been proposed for Myotonic

Distrophy (Gennarelli et al. 1994).

An attempt to quantify the HLA contribution

to the familial clustering of the disease was done

using the λsparameter. The contribution of the

HLA region evaluated on the affected sib pairs

from the present study resulted as 21±15% of the

increased risk to siblings. Indeed, the presence of

high risk HLA molecules seems a necessary but

not sufficient genetic condition since the disease

occurs in approximately 1 out of 3 sibs and 1 out

of 50 parents carrying predisposing HLA factors.

A further evaluation of these parameters was

done on a larger sample consisting of our families

and data available from the literature. A λsHLA

of

3±57, was calculated using haplotype sharing

frequency of 158 sib pairs and possibly represents

a more precise estimate of the HLA role. Hence,

the contribution of the HLA susceptible alleles

to the development of CD has been quantified as

36±2% of the increase in risk to siblings leaving a

large proportion to unidentified factors.

In the absence of logical candidate loci, a

genome-wide screening that makes use of a large

set of well spaced highly polymorphic markers

has proven to be a very powerful method for

searching for genomic regions which might

contain loci involved in genetically complex

diseases (Weeks & Lathrop, 1995). The search for

genes predisposing to CD has already been

undertaken by Zhong et al. (1996) that recently

published the results of a first screening carried

out on 45 affected sibling pairs where some

candidate regions have been identified. Even if

these results need to be confirmed in a larger

sample, they represent the first indication of a

chromosomal location of other predisposing

genes.

We are grateful to the patients and their families forparticipating in the study. We would like to thank Prof.I. Polanco and Dr M. L. Mearin for kindly providingsome unpublished pedigrees and Prof. L. Terrenato forcritically reading the manuscript. This work was partiallysupported by CNR, ‘Progetto Finalizzato IngegneriaGenetica’ and by MURST 40% ‘Immunoregolazione’.

A, P. (1974). Family studies in celiac disease. InCeliac disease (eds. W. Th. Hekkens & A. S. Pena),pp. 322–325. Leiden: Krose.

A, S., M, G., T, R., V, J.,M, M. & P, I. (1988). Celiac disease as afamilial condition: identification of asymptomaticceliac patients within family groups. GastroenterologyInternational, 1, 25–31.

B, H., G, L., D, L., B, J.,F, F. & L, J. C. (1980). Celiac diseaseand its association with HLA markers. In Hysto-compatibility testing 1980, vol. 1 (ed. P. I. Terasaki),pp. 668–672. UCLA Tissue Typing Laboratory Pub-lisher.

B, W. C. & E, R. C. (1985). A com-parison of sib-pair linkage tests for disease suscep-tibility loci. Genet. Epidemiol. 2, 85–97.

B, J. G., M, G. E., A, E. D., B,W. F., B, R. E., C, D., D, B.,E, H. A., M, B., M, W. R., P, P.,S, T., S, G. M. T., S, J.L., S, A. & T, P. I. (1995). No-menclature for factors of the HLA system, 1995.Tissue Antigens 46, 1–18.

B, W. J., H, M. A., V, R. W.,W, K. I. & C, P. J. (1991). A family studyconfirms that the HLA-DP associations with CeliacDisease are the result of an extended HLA-DR3haplotype. Hum. Immunol. 31, 100–108.

B, M., M, P., M, M. C., T,P., L, P., F, P., P, A.,M, A., G, G. & I, C. (1996).Prevalence and clinical pattern of celiac disease amongsiblings of celiac children. J. Ped. Gastroenterol. Nutr.23: 159–163.

C, C., H, G. A., N, M. J., C, P.G., K, P., F, L., M, P., G,R., F, C., W, D., S, J. A. (1990).HLA-DP and celiac disease: family and populationstudies. Gut 31, 663–667.

316 F. P

C, C., R, I. M., F, E., R, M.,B, F., C, F., C, G. V. & G,P. L. (1994). Celiac disease in the year 2000: exploringthe iceberg. The Lancet 343, 200–203.

E, A. (1981). Celiac disease: previous family studies.In The genetics of celiac disease (ed. R. B. McConnell),pp. 197–200. Lancaster : MTP Press.

F, Z. M., R, G. N. & S, W. (1972).Predominance of histocompatibility antigen HL-A8 inpatients with gluten-sensitive enteropathy. J. Clin.Invest. 51, 1602–1606.

F, P., P, F., M, P., B-, M., M, M. C. (1992). Oligotyping of Italianceliac patients with the 11th International Histo-compatibility Workshop reagents. Tissue antigens 39,38–39.

G, M., D, B., B, M., M-, I. & N, G. (1994). Meiotic drive at themyotonic dystrophy locus. J. Med. Genet. 31, 980.

G, D. A., H, S. E. & R, J. I. (1982).Evidence for recessive and against dominant in-heritance at the HLA-linked locus in coeliac disease.Am. J. Hum. Genet. 34, 263–277.

G, R., P, F., F, P., M, B.,B, M., M, M. C. (1996). Unusual HLAtyping in Celiac disease. Dis. Markers. 13, 61–64.

H, M., M, M. C., S, M. L., B, F.,B, A., B, G., C, P. J., C-, G. R., F, P., G, W., H, M.,K, A., K, E., L, J. S., M-, V., M, K., P, F., R,E., T, G., V, B. A., W, K. I., W,T. & A, E. (1992). Celiac disease study XIthworkshop report. In HLA 1991, vol. 1 (eds. K. Tsuji,M. Aizawa, T. Sasazuki), pp. 722–729. Oxford: Uni-versity Press.

H, J. L., M, J. P., MC, C. C.,MC, C. F., S, F. M. & E, R. C.(1991). Evidence for a dominant gene mechanismunderlying coeliac disease in West of Ireland. Genet.Epidemiol. 8, 13–27.

K, A. & S, T. (1992). Eleventh Inter-national Histocompatibility Workshop reference pro-tocol for the HLA DNA-typing technique. In HLA1991, vol. 1 (eds. K. Tsuji, M. Aizawa, T. Sasazuki), pp.397–419. Oxford: University Press.

L, K. E. A., S, L. M., Q, E., M-, G., G, H. A., E, J. & T, E.(1990). T lymphocyte recognition of celiac diseaseassociated cis or trans encoded HLA-DQ α,β hetero-dimer. J. Immunol. 145, 136–139.

M' , G., B, G., C, F., I, G., DD, F., P, R., C, F., M, I.,R, C., A, A., R, N., B, E.,T, G. & G, L. (1994). Increasing incidenceof childhood celiac disease in Sicily: results of amulticenter study. Acta Paediatr. 83, 1065–1069.

M, P. & A, P. (1978). HLA and coeliacdisease. Brit. Med. Bull 34, 291–294.

M, M. C., F, P., M, P., M,E., P, F., T, P. & B, M.(1992). A study of Italian paediatric celiac diseasepatients confirms that the primary HLA association isto the DQ(α1*0501, β1*0201). heterodimer. Hum.Immunol. 33, 133–139.

MK, R., S, F. M., MN, B., S,S., A, E. & MC, C. F. (1983). Family andpopulation studies of HLA and coeliac disease in theWest of Ireland. Tissue Antigens 22, 175–181.

M, M. L., B, I., P4 , A. S., P, I.,V, C., S, G.T. M., D V, R. R.P. & V R, J. J. (1983). HLA-DR phenotypes inSpanish coeliac children: their contribution to theunderstanding of the genetics of the disease. Gut 24,532–537.

M, M. L., B, J., M, N., S,E., S, M., B, I., S, G.M.T., P, A. S., V G, H. H. & V

R, J. J. (1985). HLA-DR antigens and phenotypesin Dutch coeliac children and their families. ClinicalGenetics 27, 45–50.

M, G. W. (1970). Diagnostic criteria in coeliacdisease. Acta Paediatr. Scand. 59, 461–463.

M, M., B, M., O, C., L, P.,T, S., C, S., M, I. & M-, M. C. (1986). Are DQ dimers by transassociationthe molecular basis of coeliac disease susceptibility?7th International Congress of Human Genetics, Berlin.

M, M., T, S., M, M. C., L, P.,C, S., B, M., M, I. &G, E. (1988). A study of HLA class II antigensin an Italian paediatric population with coeliac disease.Disease Markers 6, 23–28.

M, M., E-M, B., F, P. F.,MN, B. & MC, C. F. (1974). Familystudies in coeliac disease. Q. J. Med. 171, 359–369.

O, S., A, S., J, A., M, J. & G,E. (1981). Immunogenetics of childhood celiac disease:the association with HLA DR3 and DR7 in unrelatedpatients and multiply affected families. Israel J. Med.Sci. 17, 1041–1044.

O, R. (1987). Simple test of the multifactorial-polygenic model with sex dependent threshold. J.Chron. Dis. 40, 165–170.

P, F., M, G., F, P., B-, M., R, G., C, L. & M, M. C.(1993). Different dose effect of HLA DQαβ hetero-dimers in insulin dependent diabetes mellitus andceliac disease susceptibility. Human Immunol. 36,156–162.

P, A., T, P., M, P., D G-, F., G, M., G, M., P, P.,B, M., B, G. (1996). The use of athreshold serum level of antigliadin antibodies im-proves diagnostic efficiency of the test in adult coeliacdisease but is not successful as a screening test. TheItalian Journal of astroenterology 28, 70–75.

P, R., T, J. E. E. & S, L. M. (1993).On the HLA-DQ(1*0501,1*0201). associated suscep-tibility in celiac disease: a possible gene dosage effectof DQB1*0201. Tissue Antigens 41, 173–177.

P, I., B, I., V L, A., S-, I., M K, P., G, J., D’A, J.,V, C., V R, J. J. & P, A. S. (1981).Gluten sensitive enteropathy in Spain: genetic andenvironmental factors. In The genetics of coeliac disease(ed. R. B. McConnell), pp. 211–231. Lancaster : MTPPress.


R, N. (1987). Assessing the role of HLA-linked andunlinked determinants of disease. Am. J. Hum. Genet.40, 1–14.

R, C. J., K-M, T. O. & S, W. K. (1974).Family study of coeliac disease. In Coeliac disease (eds.W. T. J. M. Hekkens & A. S. Pena), pp. 320–321.Leiden: Stenfort Kroese).

R, C. J., K-M, T. B., W-K, S. &A, C. M. (1981). The familial incidence ofasymptomatic coeliac disease. In The genetics of coeliacdisease (ed. R. B. McConnell), pp 235–243. Lancaster :MTP Press.

R, P. C. M., P, A. S., H, W.T. J.M., D V, R. R. P. & H, A. J. (1978). Coeliacdisease. A family study in the Netherlands. InPerspectives in coeliac disease (ed. B. McNicholl, C. F.McCarthy & P. F. Fottrell), pp. 146–154. Lancaster :MTP Press.

S, R. T., W, A. L., K, R. & T,R. R. (1975). A family study of coeliac disease. Aust.N.Z.J. Med. 5, 250–255.

S, S. & A, E. (1983). HLA and diseases :involvement of more than one HLA-linked deter-minant of disease susceptibility. Immunological Rev.70, 77–88.

S, M. L., M, G., E, J., G, H.,V, F. & T, E. (1989). Evidence for aprimary association of celiac disease to a particularHLA-DQ α,β heterodimer. J. Exp. Med. 169, 345–350.

S, L. M. & T, E. (1993). HLA susceptibilitygenes in celiac disease: genetic mapping and role inpathogenesis. Gastroenterology 105, 910–922.

S, R. S., MG, R. E. & E, W. J.(1993). Transmission test for linkage disequilibrium:

the insulin gene region and insulin-dependent DiabetesMellitus (IDDM). Am. J. Hum. Genet. 52, 506–516.

S, L., B, A. & W, J. (1982).A family study of coeliac disease. Acta Paediatr. Scand.71, 625–628.

T, R., T, N., P, J., D M, M.,W, J. C. & H, P. H. (1986). A radio-immunoassay typing study of non-DQw2-associatedceliac disease. Clin. Immunol. Immunopathol. 39,168–172.

T, S., G, A., R, M., M, D.,C, I., T, A., M, M. C. &G, E. (1984). HLA-ABC and DR antigens inceliac disease. Vox Sanguinis 46, 102–106.

T, J. S. (1991). Celiac sprue. N. Engl. J. Med. 325,1709–1719.

T, R., C, N., Z, N., M,G., M, L. & A, S. (1992). Coeliac disease:a common food intolerance on an immunological basis.In Common food intolerances 1: Epidemiology of coeliacdisease, vol. 2 (eds. S. Auricchio & J. K. Visakorpi), pp.1–11. Basel : Karger.

W-S, J. A., G, S., S, J.,S, D. H. & V, J. K. (1990). Revisedcriteria for diagnosis of coeliac disease. Archives ofDisease in Childhood 65, 909–911.

W, D. E. & L, M. (1995). Polygenic disease:methods for mapping complex disease traits. TIG 11(12), 513–519.

Z, F., MC, C. C., O, J. M., E, R. C.,S, F. M., MC, C. F. & M, J. P.(1996). An autosomal screen for genes that predisposeto celiac disease in the western counties of Ireland.Nature Genet. 14, 329–333.

Genetic contribution of the HLA region to the familial clustering of coeliac disease

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