Breaking Gluten 1

Breaking gluten: A review of the celiac paradox and future avenues of research

Shannon Clark

Colorado State University

Breaking Gluten 2

Abstract

Celiac disease (CD) is an autoimmune disorder in which the affected experience gluten sensitive

enteropathy when gluten proteins are ingested (Mahadov & Green, 2011). Gluten is a mixture of

proteins comprised of two main classes: gliadin and glutamine, storage proteins that give

elasticity to the dough of wheat, barley, and rye (Gallagher et al., 2004). In CD sufferers the

immune system interprets the gluten protein as a pathogen and mounts an attack in response, in

turn causing inflammation and damage to the mucosal lining of the small intestine (Gobbetti et

al., 2014). Although substantial research has been directed toward pinpointing the root cause of

CD, the mechanisms leading to the development of the disease are still not fully understood

(Sams & Hawks, 2014). A review of the current literature on CD reveals a causal relationship

between genetics, gluten proteins, and other unknown environmental factors in people with CD

(Sams & Hawks, 2014). Research has put two pieces of the “celiac puzzle” together in

identifying the genetic traits and gluten proteins associated with the disease, and yet while other

environmental factors have been hypothesized to contribute to CD, their role is not fully

understood (Clemente et al., 2012). In this review I briefly cover the history of CD and the rising

world CD population, showing the geographic spread of CD from the Fertile Crescent and the

recent increase in CD prevalence (Lionetti, Gatti, Pulvirenti & Catassi, 2015) (Sams & Hawks,

2014). I summarize the current knowledge of the evolutionary history of the human leukocyte

antigen (HLA) heterodimers and non-HLA risk alleles associated with CD, and why these

genetic predispositions have not evolved out of the human population (Price et al., 1999)

(Zernakova et al., 2010) (Romanos et al., 2009). I also review the genetics of gluten-containing

cereals and the pathogenesis of CD by gluten proteins (Osorio et al., 2012). I conclude with

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suggestions for future avenues of research that may expand our understanding of the mechanisms

leading to CD and possible prevention of the disease.

Introduction

Celiac disease (CD) is one of the most common autoimmune disorders, known to affect

approximately 1% of the world population (Lionetti et al., 2015). The increase in access to

testing has improved the diagnosis rate but there is also evidence that the disease rate is

increasing, even though CD has a negative effect on the population (Lionetti et al., 2015). CD

has a genetic basis and is triggered by gluten proteins in the diet, along with other unknown

environmental factors (Clemente et al., 2012). In a person with celiac disease, the ingestion of

gluten causes an immune response as the body identifies the protein as a pathogen (Ozuna et al.,

2015). Three major immunogenic peptides have been discovered in gluten containing grains that

react with the autoantigen, transglutaminase, in celiac sufferers (Ozuna et al., 2015). These

peptides produce an inflammatory response in the gut of celiac patients, as it triggers the

activation of CD4 T cells, the body’s natural immune response to antigens (Shan et al., 2002).

The attack on the body’s immune system causes CD patients to suffer from villous atrophy, the

destruction of intestinal villi (Mahadov & Green, 2011). Atrophy causes a myriad of symptoms

including diarrhea, malnutrition, anemia, miscarriage and infertility, and general failure to thrive

due to the loss in the ability of the villi to absorb the nutrients from food (Mahadov & Green,

2011).

The History of Celiac Disease

CD is correlated with the Agricultural Revolution that occurred during the Neolithic era,

as the cultivation of crops led humans to move from hunter-gatherer existences to living in more

populated communities (Lionetti et al., 2015). These settlements began domesticating wild

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variants of gluten-containing cereal grains (wheat, barley and rye) around 10,000 years ago in the

area known as the Fertile Crescent, from the Persian Gulf down into Egypt (Brenchley et al.,

2012). Cultivation of these cereals slowly spread north into Europe, reaching the Great Britain

region about 4,000 years ago (Brenchley et al., 2012). New diseases evolved from the

Agricultural Revolution as humans living in closer quarters provided a vector for the spread of

bacteria and viruses (Zwart & Penders, 2011). The new human diet consisting mostly of grains, a

move from the biologically natural Paleolithic meat and forage-based diet, caused nutritional

deficits and new diseases (Zwart & Penders, 2011) (Sams & Hawks, 2014). Researchers

generally agree that the first instances of CD occurred shortly after this shift in diet and lifestyle

(Zwart & Penders, 2011). The oldest known description of possible CD cases in a population

dates back to 250 A.D. when Aretaeus, a Greek physician, described the intestinal and

malabsorption symptoms in sufferers of an unknown disease he called “koilikos” (Losowsky,

2008). This term was later translated into English and the disease was labelled “celiac” disease

(Losowsky, 2008). In 2008, an archaeological dig revealed a 2,000 year old skeleton of a woman

near Cosa, Italy which presented with probable celiac disease (Scorrano et al., 2014). So far this

is the oldest evidence of celiac, further proof that the disease is not a manifestation of recent

history (Scorrano et al., 2014). The underlying cause of CD symptoms was not understood until

1888, when a review of CD patients by physician Samuel Gee noted that the diet was the cause

of the symptoms, and patients appeared to improve when limiting their diets to a handful of

foods (Sams & Hawks, 2014). Then finally in the 1950s, Dutch pediatric researcher Willem

Dicke made the discovery that the gluten proteins were the underlying cause of the symptoms

presented by celiac patients and a gluten-free diet became the treatment for CD sufferers

(Scorrano et al., 2014).

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Geographical view of CD incidence

In a global review of celiac rates and wheat consumption, Lionetti & Catassi (2014)

noticed a correlation between the amount of wheat consumption in populations and the

frequencyof CD genetic traits in those populations.

Fig. 1- “Correlation between the level of wheat consumption and the frequency of HLA-DQ2” (Lionetti et al., 2015)

The human leukocyte antigen (HLA) DQ2 and DQ 8, the heterodimers associated with CD, have

very high occurrences in areas that consume high levels of wheat (Lionetti & Catassi, 2014). In

northern India where wheat consumption is very high, DQ2 and DQ8 haplotypes occur in about

30% of the population, while in southern India where wheat consumption is much lower the

frequency of these haplotypes is about 10% (Lionetti et al., 2015). This model also presents itself

in Africa, with northern populations consuming large quantities of wheat daily and also having

higher rates of the genetic predisposition for CD compared to sub-Saharan Africa and South

Africa (Lionetti et al., 2015). CD rates and its genetic markers are also increasing in other areas

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of the world, such as South America, as populations increase their consumption of wheat and

other gluten-derived cereals (Lionetti et al., 2015). It was originally theorized by Simoons (1981)

that the negative impact to fitness and survival from CD would cause negative selective pressure

on CD genes over time. According to this hypothesis the populations in the Middle East, which

have cultivated wheat since its domestication around 10,000 years ago, would have a lower rate

of CD than in Western Europe, which only started cultivating wheat 4,000 years ago (Simoons,

1981). This hypothesis was found to be unsupported with Lionetti &Catassi’s (2014) findings

that CD rates are similar in Western Europe and the Middle East, and CD phenotypes have the

highest rate of incidence in the Fertile Crescent region.

Fig. 2- “World map of frequency of HLA-DQ2” (Lionetti et al., 2015)

Fig. 3- “World map of celiac disease prevalence” (Lionetti et al., 2015)

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Multiple reviews of population CD rates have shown that regions with the longest history

of cultivating wheat and other gluten-containing cereals have the highest rate of CD and the

largest percentage of CD genetic predisposition factors (Lionetti et al., 2015). Interestingly, this

occurrence pattern of CD almost completely contrasts the occurrence pattern of lactose

intolerance, in which communities with the longest dairying history have much lower rates of

lactose intolerance (Sams & Hawks, 2014). This phenomenon supports the hypothesis that the

CD associated HLA-DQ2 heterodimer is being selected for; this has become to be known as the

celiac “evolutionary paradox” (Lionetti et al, 2015).

Casual Factors of CD

The genetic component of CD

Although genetics are not purely responsible for the pathogenesis of CD, a common

genetic profile is shared among CD sufferers (Romanos et al., 2009). Research has confirmed the

primary genetic component to the development of CD is associated with the HLA system (Sams

& Hawks, 2014). HLA genes serve to encode the proteins in the major histocompatibility

complex (MHC), which controls the functions of the human immune system (Buhler & Sanchez-

Mazas, 2011). MHC class II molecules, which acquire peptides through an exogenous pathway,

are the molecules linked with the CD antigen response (Sams & Hawks, 2014). The MHC class

II protein, HLA-DQ, is a heterodimer on antigen-expressing cells, serving to bind antigen

peptides (Buhler & Sanchez-Mazas, 2011). These proteins then deliver the antigens to T-cells to

initiate an immune response (Price et al., 1999). Through repetitive genetic studies it was found

that 90% of people with CD have serotype HLA-DQ2, while the remaining 10% have serotype

HLA-DQ8 or a combination of the two (Lionetti et al., 2015) (Sams & Hawks, 2014). There are

two loci which encode the HLA-DQ receptor αβ-heterodimers which are contained on

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chromosome 6p21.3 (Price et al., 1999). Humans produce variants of the heterodimers on these

loci and can produce 4 isoforms but usually there are 2 dominant isoforms (Sams & Hawks,

2014). There are multiple isoforms within each DQ haplotype, and some within HLA-DQ2 are

linked stronger to CD (Sams & Hawks, 2014). With each locus encoding an HLA-DQ

heterodimer a person can be a heterozygous or homozygous carrier for either HLA-DQ2 or

HLA-DQ8, or they can carry both HLA-DQ2 and HLA-DQ8 (Sams & Hawks, 2014). Research

on CD patients has shown that homozygous carriers have a much greater potential for developing

CD (Sams & Hawks, 2014)

It would naturally be assumed that the imposed fitness and reproductive costs on CD

carriers would create a negative selection pressure on the CD linked genotypes, but this has not

been the observed pattern as CD occurrence is increasing (Lionetti & Catassi, 2014). It has been

hypothesized that there is a balancing selection occurring, in which the HLA-DQ2 genes are

being actively selected for because the benefit they provide outweighs the fitness cost associated

with the risk of potential immune diseases (Lionetti et al., 2015) (Sams & Hawks, 2014). One

hypothesis is that selection of HLA-DQ2 haplotypes provided protection against pathogens

which were brought on by the rise of the Agricultural Revolution (Lionetti et al., 2014). Higher

rates of pathogen-related diseases such as dental caries and tuberculosis were observed during

the transition from the Holocene era as communities moved to agricultural production (Sams &

Hawks, 2014). In one of the largest studies of the HLA gene complex, Buhler &Sanchez-Mazas

(2011) found significant values in Tajima’s D for the alleles in the DQ loci, showing a lack of

allelic diversity. HLA alleles are usually extremely variable in comparison to other gene

complexes (Buhler & Sanchez-Mazas, 2011). The aforementioned study provided strong

evidence that the CD associated HLA genes have undergone balancing selection throughout

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human history (Buhler & Sanchez-Mazas, 2011). Research by Price et al. (1999) revealed that

the HLA 8.1 ancestral haplotype (AH), in which the HLA-DQ2 gene is included, is associated

with many immunopathological diseases and is also highly conserved in the population. The

highly conserved genomic sequences within this AH suggest a common ancestor (Price et al,

1999). This could support the theory of CD being contributed to a founder effect, but a search of

the literature does not provide any further evidence of a founder effect. Also, the continual

increase of CD in the population through various people groups suggests the genetics are being

actively selected for and not just contributed to a common ancestor (Sams & Hawks, 2014).

When Price et al. (1999) mapped the concentration of HLA 8.1 they reported an observed

resistance to recombination in the population. The conservation of this AH further supports the

theory of balancing selection as the genotypes associated with CD and other immune related

diseases are resisting polymorphism (Price et al., 1999).

In 2007 a Genome Wide Association Study (GWAS) identified non-HLA risk loci

associated with celiac (Van Heel et al., 2007). Although the HLA risk loci account for the

majority of the known genetic risk of CD (approximately 40% of the 50% known risk), these

non-HLA risk loci make small contributions to the CD risk and have come to be known as

“background” risk loci (Zhernakova et al., 2010). GWAS has also determined many CD risk loci

that are shared among immune disorders, further explaining the link of CD to other autoimmune

conditions (Zhernakova et al., 2010) (Kumar et al., 2012). In total, 39 non-HLA risk loci have

been found to be associated with CD in the most comprehensive study to date by Tyrnka et al.

(2011). Using a fine-mapping study and employing the use of the Immunochip, Tyrnka et al

(2011) identified all the associated risk loci currently known. Sams & Hawks (2014) conclude

that these “background” risk loci have been driven by different environmental factors faced in

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populations, leading to selection of certain risk loci among populations in a similar environment.

In a study by Zhernakova et al. (2010) the team assessed 10 of the CD risk associated loci and

found evidence of positive selection among 3 of the loci. Further research into the haplotype

containing the SH2B3 risk allele revealed its association with many immune disorders

(Zhernakova et al., 2010). In a further test, individuals carrying the SH2B3 risk allele

demonstrated a greater inflammatory cytokine response (Zhernakova et al., 2010). Cytokine is

known to provide protective factors in bacterial infections, which led Zhernakova et al. (2010) to

hypothesize an evolutionary positive selection on the SH2B3 due to pressures by bacterial

pathogens. More research in this area is needed to further support this hypothesis. Research by

Romanos et al. (2009) of the non-HLA risk loci carried by individuals with CD versus controls

showed that individuals carrying more than 13 risk alleles had a much higher incidence of CD.

This provides a possible avenue to test the likelihood of an individual to develop CD based on

their genetic composition. A review of current research on the genetic components involved in

CD points to a combination of a balancing selection of the HLA-DQ2 and HLA-DQ8

heterodimers, along with environmental factors creating a positive selection for “background”

risk loci, to create the known genetic CD predisposition.

Environmental factors

The major environmental factor lies with the ingestion of gluten-containing products, as

successful treatment of CD symptoms is achieved with a GFD (Gallagher, Gormley & Arendt,

2004). The consumption of gluten-containing cereal grains occurs almost world-wide and the

genetic predisposing CD factors occur in upwards of 30% in some populations, yet the global

incidence of CD is around 1% (Lionetti et al., 2015). This discrepancy demonstrates that genetics

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and the gluten trigger are not the sole cause of CD, which suggests that other environmental

factors are partly responsible for the pathogenesis of the disease (Clemente et al., 2012).

The gluten protein

Gluten is a water insoluble mixture of storage proteins found in wheat with variations in

barley and rye (Osorio et al., 2012). This mixture of proteins is what gives these cereal grains

their elasticity and unmatched qualities, especially the qualities found in bread and pasta made

from gluten-containing grains (Osorio et al., 2012). The components of this protein are the main

environmental trigger contributed to CD pathogenesis (Sams & Hawks, 2014). Gluten is mainly

comprised of two classes of proteins: gliadins and glutenins (Osorio et al., 2012). These peptides

are proline-rich which prevents their complete digestion by gut enzymes (Osorio et al., 2012).

Proline is a unique α-amino acid with a secondary amine pyrrolidine (Ozuna et al., 2015). When

gluten-containing cereals are ingested by CD sufferers, these peptides are transformed to

glutamate by tissue transglutaminase 2 (tTG2) allowing them to bind to the HLA-DQ2 and HLA-

DQ8 molecules, delivering them to the T-cells in the gut (Shan et al., 2002). The T-cells view the

gluten peptide as an antigen and initiates the body to produce cytokines, which cause

inflammation and lead to damage of the mucosal lining in the intestines (Shan et al., 2002).

There are many variations of gluten peptides contained in wheat, barley and rye that cause an

immunogenic response, with different species within these grains containing their own unique

peptides (Ozuna et al., 2015). Wheat α-gliadin proteins contain three major immunogenic

peptides resulting from the partial digestion breakdown of gluten: the p31-43, the 33mer, and

DQ2.5-glia-α3 epitope (Ozuna et al., 2015). These peptides, especially the 33mer, show a strong

immune response to T-cells from people with celiac (Shan et al., 2002).

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Wheat varieties and immunogenicity of gluten

Triticum aestivum, bread wheat, originated approximately 8,000 years ago with the

hybridization of Triticum dicoccoides (AABB, tetraploid emmer wheat) and Aegilops tauschii

(DD, diploid goat grass) (Brenchley et al., 2012). There are three associated genomes which are

traced back to the common ancestor Triticeae around 2.5-4 million years ago: AA from Triticum

urartu, BB most likely from Sitopsis, and DD from Aegilops tauschii (Brenchley et al., 2012).

People with CD have various responses to the immunogenic peptides found in wheat, barley and

rye, making it difficult to genetically modify cereals to remove the peptides that elicit a T-cell

response (Ozuna et al., 2015). In 2005, Molberg et al. mapped the gluten T-cell epitopes from the

AA, BB, and DD genomes of bread wheat to identify which species had immunogenic responses

to T-cells of celiac patients. They found that the highly immunogenic 33mer epitopes were

encoded on wheat chromosome 6 D, therefore not contained in the gluten proteins of diploid

einkorn (AA) and many cultivars of tetraploid (AABB) wheat (Molberg et al., 2005). This study

paved the way for further research in the breeding of wheat species with no or low levels of

immunogenic peptides that would be suitable for people affected by CD (Ozuna et al., 2015).

The recent sequencing of α-gliadin genes in diploid, tetraploid and hexaploid wheat by Ozuna et

Fig. 4- Pathogenesis of celiac disease. Gluten peptides that are highly resistant to intestinal proteases reach the lamina propria. Reaching lamina propria the epitopes get crosslinked and deamidated by tissue transglutaminase 2 (tTG2) and presented via HLA-DQ2 (-DQ8) on the surface of antigenpresenting cells (APC). Subsequently, CD4+ T cells are activated; as a result, the secretion of Th1 cytokines will trigger the release and activation of metal proteinases by myofibroblasts, finally resulting in mucosal remodeling and villous atrophy (Osorio et al., 2012)

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al. (2015) identified 6 types of α-gliadins. Furthermore, Ozuna et al. (2015) found that the 33mer

epitope was contained only in hexaploid wheat, as a result from the D-genome contributor. This

study confirmed the findings of the research done 10 years earlier by Molberg et al. (2005) in

which the D-genome was identified as the encoder of the 33mer epitope, but it also provided a

basis for further research using advanced genome-editing techniques such as CRISPR to breed

wheat varieties that have low immunogenic T-cell responses (Ozuna et al., 2015). The research

done by Molberg et al. (2005) along with a current study by Gianfrani et al. (2015) show a

promising potential for the use of low-toxic diploid wheat in relatives of CD patients with

predisposing HLA haplotypes to delay or prevent the onset of celiac. Gianfrani et al. (2015) is

currently performing further experiments to test the potential of low-toxic diploid wheat species

in the diet of CD sufferers.

Enzymatic approaches to gluten breakdown

While the selective breeding for wheat varieties with no or low levels of immunogenic

peptides and epitopes has been extensively researched, there is yet to be a successful wheat

variety produced without immunogenic effects to CD sufferers. The difficulty of breeding a

wheat species with immunogenic peptides is largely contributed to people with CD experiencing

various reactions to the different gliadin peptides (Osorio et al., 2012). Another option of

reducing the toxicity of immunogenic peptides in wheat is the use of enzymes to break down

gluten peptides rich in glutamine and proline; this method provides some potential new options

for the treatment of CD (Gobbetti et al., 2007). To reduce immunogenic properties the proline

and glutamine peptides can be cleaved before they enter the intestinal track (Clemente et al.,

2012). Gobbetti et al. (2007) showed the ability of fungal proteases and sourdough lactobacilli to

break down peptides through a long fermentation process. Baked goods using this hydrolyzed

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wheat were given to CD patients; complete tolerance was demonstrated among all the subjects

(Gobbetti et al., 2014).

Shan et al. (2004) and Piper et al. (2004) verified the ability of prolyl endopeptidases

(PEP) to cleave proline and glutamine peptides and produce detoxification. Further research has

also demonstrated the ability of these enzymes to breakdown these gluten peptides (Clemente et

al., 2012). Cysteine endoproteases (EP) have a similar ability to cleave glutamine residues, and

can work with a prolyl endopeptidase to significantly reduce the immunogenic effects of the

gluten protein (Osorio et al., 2012).

Fig. 5- “Schematic representation of the proteolysis during sourdough fermentation. (A) Primary proteolysis triggered by the acidification and the reduction of disulfide bonds of gluten by hetero-fermentative lactobacilli, which, in turn promote the primary activity of cereal proteases, which lead to the liberation of various sized polypeptides. (B) Secondary proteolysis by intracellular peptidases of sourdough lactic acid bacteria, which complete the proteolysis and liberated free amino acids. (C) Catabolism of free amino acids by sourdough lactic acid bacteria: example of catabolic reaction involving phenylalanine” (Gobbetti, 2014)

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Currently researchers are working on producing a pill that includes the PEP and EP

enzymes to be taken with gluten consumption to break down immunogenic peptides (Osorio et

al., 2012). However, this might not be the most cost-effective and easily enacted approach. In a

review, Osorio et al. (2012) assessed the ability of cereal grains to synthesize and store the PEP

and EP B2 enzymes to detoxify gluten peptides at the source. Their review concluded that it

would be promising to attempt this approach, providing a new and cost-effective approach to CD

treatment (Osorio et al., 2012).

Other environmental factors- The gut microbiome

The microbiome area of CD research is probably the most conflicting and controversial.

With an epidemic rise in CD in Sweden during the 1980-1990s researchers began to hypothesize

that the large decrease in breastfeeding during this time led to the increased rate of the disease

(Ivarsson et al., 2013). Various retrospective studies found that breastfeeding provided an

increased protection against CD, causing the development of many hypothesizes of how the lack

of breastfeeding was linked to CD pathogenesis (Akobeng et al., 2006) Many studies have since

reputed these claims, finding no evidence linking breastfeeding to a decreased risk of CD

(Lionetti et al., 2014) Although contradictive results have been found in many studies, the

importance of the gut microbiome to CD pathogenesis remains a common theme in the research

of environmental causal factors. The gut microbiota have been attributed with playing a large

role in metabolism, digestion and initiation of immune response to pathogens, specifically

because they encode genes that are not present in the human genome (O’Hara & Shanahan,

2006). In 2014, David et al. and Goodrich et al. released studies showing that both genetics and

environmental factors work together in the formation of the gut microbiome. This is further

evidence that the gut microbiome plays a role in the formation of CD. In a recent review of

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microbiota and CD, Cenit et al. (2015) presented a model of how disruption of microbiota

homeostasis in the gut might lead to the development of diseases.

There is a lot of evidence for the model proposed by Cenit et al. (2015), as GWAS

studies have shown that many genes responsible for immune response also play a role in shaping

the gut microbiota. One study found the rod-shaped bacterium, Lachnoanaerobaculum umeaense,

in the guts of people with CD but not in the guts of controls (Forsberg et al., 2004). In 2013,

Sjöberg et al. demonstrated a relationship between this rod-shaped bacteria and a specific

cytokine involved in anti-bacterial responses. Although much research has been done in the area

of the human gut microbiome, nothing has yielded an answer to the association of environmental

factors to the cessation of gluten tolerance.

Future avenues of research

A thorough review of CD presents many avenues of further research. The increasing rate

of CD presents a problem that must be managed and dealt with immediately. I believe this needs

to be a multi-faceted approach that involves improved and low-cost screening methods, removal

of immunogenic properties from gluten-containing cereals by genetically modifying cereal

varieties, the use of peptide degrading enzymes, and improvement in the baking qualities and

cost of naturally gluten-free grains. Within the past year there of been a lot of promising research

Fig. 6- “Proposed model for celiac disease (CD) pathogenesis. Specific host genetic makeup and environmental factors could promote the colonization of pathobionts and reduce symbionts, thus leading to dysbiosis. Dysbiosis may contribute to disrupting the immune homeostasis and gut integrity, thereby favoring CD onset and aggravating the pathogenesis” (Cenit et al., 2015).

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that addresses these approaches. Almazán et al. (2016) developed and tested a non-invasive

method to test for celiac that involves just the prick of a finger. Subjects that test positive can

then be identified to undergo further testing to positively diagnose CD (Almazán et al., 2016).

This is both a low-cost and easy method that could be implemented in schools and pediatric

offices worldwide to screen children for the disease and significantly increase the diagnosis rate.

This method would also allow for the early initiation of a GFD, preventing the plethora of long

term health effects associated with undiagnosed CD. Until non-toxic gluten-containing cereal

varieties are available for use by CD sufferers, continued research of naturally gluten-free grains

is important. Researchers at Kyoto University just announced that they have mapped the entire

genome of buckwheat (Yasui et al., 2016). Buckwheat is naturally gluten free, making it a great

option for use in a GFD. The mapped genome will allow genetic modification of many

buckwheat traits, including improving the texture in baked goods made from buckwheat, making

it more like the qualities found in wheat (Yasui et al., 2016).

Although there is ample research on CD pathogenesis, there is still a missing piece to the

puzzle of what is causing CD to develop in 1% of the population. The genetic component and the

major environmental trigger have been identified, yet CD occurs in only a small percentage of

people with those two risk factors. The other risk factor(s) remains to be determined, and

identification of this factor(s) could lead to a cure for CD, instead of just treatment of the disease.

With closely related autoimmune disorders, such as type-1 diabetes, associated with the HLA-

DQ2 and DQ-8 heterodimers, the missing “puzzle piece” might also lead to a cure for other

immune diseases. I think that there needs to be further research into the use of a GFD in

individuals with the HLA-DQ2 or DQ8 heterodimers to prevent the potential onset of other

autoimmune disorders. Another area that needs to be further researched is the topic of

Breaking Gluten 18

fermentation in bread baking. The study by Gobbetti et al. (2007) showed the sourdough

fermentation process to be capable of breaking down gluten proteins. Historically bread was

made using a fermentation process, unlike commercially produced bread today (Gobbetti et al.,

2014). This could be a potential theory to the cause of the rise in the CD rate. Interestingly, in my

review of the literature covering CD I did not find any research in the area of gluten-containing

cereal grains and their metabolites. Jackson (1996) hinted at the possibility of coevolutionary

effects between humans and domesticated crops. Plant metabolites should be explored as the

complete cause of CD remains a mystery and funding continues to increase towards CD related

research.

Conclusion

Since the discovery of the gluten protein as the main trigger of CD in the 1950’s there has

been a wealth of research conducted in many areas of the disease- the cereal grains and gluten

protein, the genetic components, and the gut microbiome. Yet all the factors that lead to the

manifestation of CD have not been identified. As the disease rate continues to increase research

needs to continue to find answers to this evolutionary paradox in order to halt the rise of

incidence. Going forward new avenues of research, such as enzymatic potentials and plant

metabolites, need to be explored as potential answers to the unknowns.

Breaking Gluten 19

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