Introduction
Contemporary technology has all but conquered the diagnosis of communicable diseases, but non-communicable diseases remain a major challenge. Among the most challenging non-communicable diseases to diagnose are those whose advent is based on genetics. Celiac disease is an autoimmune disorder that occurs as a result of genetic predisposition. Therefore, based purely on genetics, an individual will or will not be susceptible for the advent of celiac disease. For individuals with high susceptibility, the advent of the disease will be triggered by environmental factors such as eating a gluten diet (Tye-Din et al., 2015). Once gluten is detected in the system, the body’s own immune system will get a false alarm and attack the villi in the small intestines. The damage of these villi compromises proper absorption of nutrients. Celiac disease provides a textbook example of diseases whose diagnosis has remained a challenge in spite of intense research and contemporary advancements in technology. Yet it is in genetically based diseases such as Celiac where accurate diagnosis that is also cost effective is paramount. This is because once a family member has been diagnosed, it is important for all other family members to undergo testing even if they are not symptomatic (Romanos, 2011). The initial and simplest test for Celiac is the antibody test. However, this test is not definitive and, therefore, cannot be relied upon except when the findings are positive. A more advanced test is the molecular test, based on the HLA-DQ2 (DQ2) molecules. Further, there is also the DNA test that determines whether or not an individual is susceptible to the advent of Celiac. The DNA test definitively rules out any future advent of Celiac with individuals found to be susceptible needing continued antibody tests. The surest way to definitively test for Celiac is through a biopsy, but this is too expensive and time-consuming to be done effectively for a larger section of the population (Romanos, 2011). The diagnosis of Celiac disease, therefore, remains a major challenge in the contemporary healthcare system, thus necessitating continued advanced research in a bid to simple definitive testing.
Celiac disease prevalence varies from region to region. In extreme cases, prevalence can be as high as 1 out of every 40 people while on the lower side it is at 1 out of every 300 people. The average prevalence, however, is between 1 out of 100 people and 1 out of 170 people. 83% of the affected remain undiagnosed with a majority of them being asymptomatic (Unicersity of Chicago Celiac Disease Center, 2017). Among children, approximately 43% of all celiac patients are asymptomatic, making the ratio lower than that among grownups. Among the primary symptoms of the disease is weight loss or failure to gain weight due to insufficient nutrient absorption. A patient may also have a loose, pale and greasy stool. As the condition develops, acute diarrhea may be experienced with the stool being pale and high in volume and with an abnormal smell. Lactose intolerance may then ensue (Romanos et al, 2008). Bloatedness of the stomach and mouth ulcers are also common symptoms.
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Challenges in the Clinical Diagnosis of Celiac
By its nature, Celiac is like a chain reaction as it is a combination of nature and nurture. According to the article by University of Chicago Celiac Disease Center (2017), for Celiac to develop, the individual must have a genetic predisposition. Indeed, for all first degree relatives of confirmed patients, prevalence is approximately 1 in every 22 while in second-degree relatives, prevalence is 1 in every 39. Also, the individual needs to take a gluten based diet, which will develop the autoimmune disorder thus being considered as suffering from Celiac. The simplest and most straightforward part of the celiac diagnosis is the diagnosis for celiac susceptibility, based on DNA testing according to Fasano et al. (2015). This is because DNA will definitely determine whether or not an individual has any susceptibility of ever contracting celiac in their lives. Individuals whose tests show negative Celiac susceptible genes such as HLA-DQ2,-DQ8, the DNA results mark the end of the diagnostic journey (Wolters, 2009). For those found to be susceptible, a lifelong nightmare of continued testing which only ends in the unfortunate case of a positive diagnosis begins. Therefore, the main challenge relating to the diagnosis of Celiac is that most procedures are only considered to have worked if they produce a positive result. A negative result ought to be considered as a reason for more tests. The situation gets worse when someone develops symptoms congruent to those of Celiac but the initial diagnosis provides a negative result. It becomes expedient to get a clear diagnosis so as to rule out or confirm celiac and enable the advent of comprehensive treatment (Wolters, 2009).
Another challenge relating to the diagnosis of celiac is the existence of too many guidelines, issued by different professional organizations and many a time contradicting one another. The different tests available for celiac apart from the DNA test and biopsy are all equally ineffective, unless they provide a positive result (Wolters, 2009). The level of ineffectiveness between these different systems is, however, a moving target with different experts indicating a preference for a particular diagnosis. This has caused different professional organizations to issue directives, which contradict one another; a factor that often creates a clinical dilemma on which directive to follow. In this day and age when negligence and lawsuits are such a major threat to the practice of medicine, conflicted directives can be a major challenge. Finally, there has been a lot of publicity about celiac more so in the developed world such as the USA. Many individuals and families are now requesting for diagnosis for celiac with other even self-diagnosing. Insurance companies have also joined the fray, recommending testing for susceptibility as part of the normal testing for some life covers. This has placed a lot of pressure on the celiac diagnosis system that is already struggling due to the complex and non-definitive nature of the tests. These challenges are expected to continue until a simple, cost effective yet definitive diagnosis for celiac is arrived at.
Available Molecular Testing for Celiac Disease
Molecular testing is one of the most complex, yet non-definitive methods for testing celiac. The molecular test is closely related to the DNA gene test albeit at a more advanced level as it checks for human leukocyte antigen (HLA) risk molecules. This can be considered as a second tier test after the DNA test, which usually tests for the existence of general susceptibility (Kaukinen, 2002 The molecular test looks further into the HLA to assess the level of the actual risk of celiac so as to either determine its advent, its probability or rule it out altogether. Considering that genes are tiny and complex materials, molecules attributed to them are tinier and more complex. According to Koskinen et al. (2009), the main premise for the preference of molecular diagnosis lies in the fact that the other option available is a biopsy. Most probable celiac patients who undergo diagnosis are small children whose parents are normally not agreeable to the invasive biopsy. They are, therefore, more willing to try the more complex molecular test, in the hope of avoiding a biopsy (Withoff, Jonkers, & Wijmenga, 2016).
Among the available HLA molecular risk tests is an algorithm based software used to assess the level of molecular risk based on a blood sample drawn from a potential celiac patient. The procedure is extremely sophisticated as it uses advanced computerized technology with specialized software developed to detect the risk probability of molecules kindred to the HLA. Specially trained experts are also necessary (Romanos et al., 2008). As a precursor to this process, there is the initial process of amplification and hybridization of the molecules that take a multistep procedure. Another simpler and cheaper molecular diagnosis procedure is based on testing for the DQ2.5, DQ2.2, DQ7, and DQ8 genotypes that are also known to engender risk within HLA (Monsuur et al, 2008).
Utility of HLA Genotyping in Molecular Diagnosis and Screening for Celiac Disease
A gene is a section of DNA that determines the characteristics of the cells formed within an organism. Genes are made up of different DNA molecules with the nature, setting and arrangement of the molecules determining what kind of resultant cell will be created. Genetic typing is a forensic process that seeks to understand a genetic manifestation through evaluating the genes themselves. Human leukocyte antigen (HLA) is a protein that functions as a marker for every cell in the body and identifies friend or foe to the antibodies, who then attack anything that is seemed to be a foe (Tye-Din et al., 2015). HLA typing entails evaluating the molecules within the HLA of a particular human to see if there exist molecules that create a possibility for being triggered by gluten so as to mark villi as foes and occasion an autoimmune attack on them. In 70% of all populace, the HLA does not have alleles with molecules that cause celiac propensity. This group is easily identifiable through DNA testing as aforesaid. It is within the 30% that HLA typing is necessary to test for the existence of HLA alleles with disease-causing molecules. Celiac disease has high association with the HLA-DQ2 and HLA-DQ8 . It is approximated that 95% of patients with celiac disease express HLA-DQ2 while only 5% are HLA-DQ8 positive. It is, therefore, evident that either HLA-DQ2 or HLA-DQ8 is essential for development of the disease but is insufficient for its development. Indeed, research estimates its risk effect at between 36 and 53%. DQ2 and DQ8 are prevalent in between 30% and 40% of healthy population. Research conducted using twin samples has revealed that HLA-DQA1 loci and HLA-DQB1 loci create susceptibility for celiac. Various polyphonic molecules are encoded by the aforesaid two genes. For example, DQ2 is a group of DQ2.5 and DQ2.2. Research has found HLA-DQA1*0505 allele of DQ7 and HLA-DQA1*0501 alleles of DQ2.5 present in 90% to 95% of all celiac patients, on the other hand, DQ8 (HLADQA1* 03, HLA-DQB1*0302), account for 6% to 10% of all European Celiac patients (Megiorni, 2012; Monsuur et al, 2008). Molecular testing, therefore, entails seeking to establish the existence of HLA alleles containing molecules that enhance propensity for celiac. Traditional methods used for this include PCR-single-strand conformation polymorphism (SSCP), sequence-specific oligonucleotide probing (SSOP) and PCR sequence-specific primer kits (PCR-SSP).
HLA Tagging SNPs Method
Single-nucleotide polymorphism (SNP) refers to a variation in the manner in which a single nucleotide occurring at a specific position in a genome differs from the common position within a population. It is, therefore, possible to use SNP to determine if an individual differs from the majority, hence susceptible to an ailment that is only limited to a minority of the population (Saadah et al., 2015). Celiac only happens to about 1% of the population in the western world, a statistic that qualifies as an extreme minority. Therefore, there will be a sequencing anomaly within the genetic coding of this minority that can be detected using the SNPs method. Further, it is already established that for Celiac, the abnormality is kindred to HLA. Therefore, a way was developed where an HLA typing, using the SNPs method can be used to assess the susceptibility of a patient to celiac (Saadah et al., 2015). This is achieved by testing of the coding within the HLA differs from the majority and in what manner. For the process to succeed, a proper understanding of the normal HLA coding is necessary. This will enable researchers to check the HLA of the suspected sample against the ordinary sample to see if some allele within the HLA shows diversity from the perspective of the SNPs method. The establishment of this will enable the HLA typing based on that particular allele, thus exponentially narrowing down the field for molecular risk diagnosis (Saadah et al., 2015).
Advantages of HLA Tagging SNPs Method as compared to traditional methods
The traditional methods of HLA typing as listed above are generally limited to the testing for DQ2 and DQ8. This exponentially reduces their sensitivity and specificity as testing tools, which are akin to reliability and validity in normal research. Sensitivity can be defined as the capability of arriving at an accurate positive result while specificity is the ability to arrive at a correct negative result. On the other hand, SNPs method as defined above tests for DQ2.2, DQ2.5 and DQ7 and DQ8. This exponentially enhances the specificity to stand at > 96.8% and sensitivity which is at a near perfect > 99.4%, of the testing, thus increasing accuracy. With a majority of celiac patients, up to between 90% and 95% having the DQ2.5 based alleles of HLA, the accuracy of the SNPs method clearly supersedes that of the traditional methods (Romanos et al., 2009). Other than its high accuracy levels, the SNPs method is cheaper, easier and faster as it uses the Polymerase chain reaction (PCR) technique. This is as opposed to the traditional methods which require repeated tests seeking for different molecule based alleles. The repetitive nature makes the traditional methods time consuming, complex and extremely expensive. The limited accuracy of the traditional methods is also still reliant on the quality of the DNA sample but DNA quality does not affect the efficacy of the SNPs method. Finally, the traditional methods have a DNA: ~150ng/reaction which is exponentially inferior to the SNPs method which has a DNA: ~8ng/reaction rate (Romanos et al., 2008).
Conclusion
Celiac can be considered as a genetic condition that triggers an adverse autoimmune reaction to gluten diets. A Celiac patient develops HLA alleles that have molecules, which when they react with gluten, mark villi in the small intestines as targets for antibody action. The antibodies proceed to attack and destroy the aforesaid villi, thus creating full-blown celiac disease. Most people with celiac may not be symptomatic and, therefore, may not even be aware that they suffer from the condition. When symptomatic, however, the disease mirrors the symptoms of normal nutrient absorption disorders with the main difference being that avoiding gluten extenuates the symptoms. With celiac being a genetic disease, having a close kinship with a patient automatically creates a higher propensity for an individual to suffer from the same. This has created a major need for proper diagnosis procedures. Unfortunately, accurate diagnosis can only be carried out through a biopsy, which is invasive and also expensive. It is for this reason that molecular diagnosis procedures have been developed in an attempt to limit the number of potential patients in need of biopsies, more so amongst children. Molecular diagnosis is based on testing for the existence of HLA alleles that have molecules, which increase celiac propensity. The procedure enables the ruling out of non-potential patients with those found culpable being marked for further testing.
References
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