Understanding Diabetes

Article Submitted by Diana Allen

Susan Morgan Bell
Pfizer: Scientific and Laboratory Services: Senior Stability Administration Associate
B.S. Environmental Science/Chemistry
A.S. Biological Sciences
Patented: Activation Tagging (ATTAG) -Plant Genomics “Isolation of Mutation in Plant Expression”

It is sighted that the World Health Organization estimates that 220 million people are suffering from Diabetes today and will double by 2030. The WHO articles draw out that the factors are sorely not exclusive to genetics only but possibly the combination of environmental factors along with genetics. It is very clear to understand why this disease is so prevalent, hard to control and not easy to understand its intricacies.

In a research article titled Etiology and Pathophysiology::Leaky gut and diabetes mellitus: what is the link?” there were several research studies that were conducted which provided enough data to question rather or notdysfunctional-regulation of the intestinal barrier or alterations in the intestinal permeability, also known as leaky gut syndrome, is directly related to diabetes mellitus. The direct link imposes that the access of infection agents and dietary antigens to the mucosal immune elements causes immune reactions which can damage the pancreatic beta cells. The damage to the beta cells can then lead to increased cytokine production which results in insulin resistance.

In an article written by M. Jagannathan titled “Toll-like receptors (TLR) regulate B cell cytokine production in patients with diabetes”, it was studied and tested that “altered TLR function in B cells from diabetes mellitus patients increases inflammation by two mechanisms: elevation of pro-inflammatory IL-8 and lack of anti-inflammatory/protective IL-10 production”. To note that Cytokines are a large group of proteins, peptides or glycoproteins that are secreted by specific cells of immune system. They play a significant role in the communication between cells in general. . In type 1 diabetes, the body’s immune system mistakenly destroys the beta cells.

According to Nutritionist “Willie Victor” Leaky gut syndrome diagnoses in a patient monitored for allergies discovered that simple foods digested daily such as dairy, soy, sugar, caffeine and gluten proved to impact the patient’s sensitivities. These sensitivities that were monitored and tested in the patient proved to be the outcome of several health issues. There are hundreds of research studies that are now emerging with significant positive results that can conclude diet is directly related to the promotion of Diabetes Type I in animals and humans.

In the first article noted above “Etiology and Pathophysiology: Leaky gut and diabetes mellitus: what is the link?” Intestinal permeability (IP) also known as Leaky Gut is defined as “the small intestine becomes damaged in which causes undigested food particles that are not filtered which go directly into the blood stream”. Damaged cells inside the gut “Intestinal mucosal cells” become compromised and therefore resulting in cellular junction separation. In having sensitivities causes the person’s body to produce antibodies recognizing that the food ingested was foreign and therefore produced antigens to fight off. The picture below gives a better understanding of these concepts.

The author makes note that an altered barrier function as shone above can “facilitate and increase exposure to antigens that can trigger immune reaction and autoimmune destruction and alterations of normal body function”.

A study was conducted with using “biobreed diabetes-prone rats, an inbreed line in which autoimmune diabetes spontaneously develops when weaned onto a regular diet. In that study the percentage of goblet cells was higher in the diabetic-prone rats compared to the diabetic-resistant rats”. The goblet cells produce mucus warding possible pathogens which suggests the present of inflammatory response, which then can lead to onset.

The author also notes, “Based on the data in animal models, pre and probiotics may have therapeutic potentials in diabetes mellitus by favoring a beneficial microbial composition and reinforcing the intestinal barrier.” These dietary studies have not been proven however, they do provide some glimpse of hope for future research and treatment. The authors final conclusions point directly to the relationship between diabetes and the gut (the effects of gastrointestinal morphology), immune response and intestinal microbiota.

Possible Modes of inheritance of Diabetes:

Some rare forms of diabetes result from mutations or changes in a single gene and are called monogenic. In the United States, monogenic forms of diabetes account for about 1 to 4 percent of all cases of diabetes. In most cases of monogenic diabetes, the gene mutation is inherited from one or both parents. Sometimes the gene mutation develops spontaneously, meaning that the mutation is not carried by either of the parents. Most mutations that cause monogenic diabetes reduce the body’s ability to produce insulin, a protein produced in the pancreas that helps the body use glucose for energy.

Neonatal diabetes mellitus (NDM) and maturity-onset diabetes of the young (MODY) are the two main forms of monogenic diabetes. NDM occurs in newborns and young infants. MODY is much more common than NDM and usually first occurs in adolescence or early adulthood.

In a research Article titled CANINE GENETIC and Epidemiology “Searching for “monogenic diabetes” in dogs using a candidate gene approach” Short, Andrea: 2014, a randomly selected group of pure breed dogs were tested. Canine diabetes is like some forms of human diabetes; it is relatively common in dogs, and its prevalence (the proportion of dogs affected at a point in time) ranges from 0.005% to 1.5% and is dependent on which breed is being considered. Canine diabetes has been compared with human type 1 diabetes (T1D), as they share many clinical and pathophysiological features. However, in contrast with T1D, which is usually diagnosed in young patients (<30 years of age), canine insulin-deficiency diabetes (IDD) occurs more commonly in older dogs, aged 7–12 years.

The aetiology and underlying pathogenesis of canine IDD has not been fully determined, although exocrine pancreatic disease and immune-mediated mechanisms are suspected to be underlying causes of pancreatic beta cell destruction. It has also been suggested that, in many ways, canine diabetes resembles latent autoimmune diabetes of the adult (LADA) in humans, a more slowly progressive form of autoimmune diabetes.

“Pedigree dog breeds, like some ethnic groups in the human population, display variability in diabetes susceptibility, with some breeds (e.g. Samoyed) being over-represented, whereas others (e.g. Boxer) seem to be relatively resistant to developing the disease”.

As mentioned above a small proportion of human diabetic patients suffer from disease resulting from mutation(s) in a single gene. These monogenic forms of diabetes account for around 1-5% of human diabetes cases and include maturity onset diabetes of the young (MODY) and neonatal diabetes mellitus (NDM). MODY represents a heterogeneous group of disorders that are commonly diagnosed before 25 years of age in humans. They result from autosomal dominant mutations in genes that control the synthesis or secretion of insulin by the pancreatic beta cells and include HNF4A (MODY1), GCK (MODY2), HNF1A (MODY3), PDX1 (MODY4) and HNF1B (MODY5).

Selective deletion of the Hnf1beta (MODY5) gene in beta-cells leads to altered gene expression and defective insulin release.

To date the genes that have been identified as causing monogenic types of diabetes in humans have not been evaluated in the diabetic dog population, where it is possible that some breeds may express a monogenic form of the condition. The aim of the present study was to screen single nucleotide polymorphisms (SNPs) from eighteen genes that have been associated with human MODY/NDM in seventeen dog breeds in order to correlate them, canine diabetes breed-related genetic susceptibilities. Although samples sizes were relatively small for some breeds examined it has been recognized that only 20–50 affected dogs are usually required for identifying conditions with a monogenic aetiology.

Breeds used in the study and overview of SNP analysis Control Group

Breed	Case (n) Genotyped	After QC	Control (n) Genotyped	After QC	SNPs (n) After QC
Bichon Frise	29	28	29	29	47
Border collie	82	76	82	79	49
Border terrier	26	24	28	25	50
Cairn terrier	45	42	45	39	52
Cavalier King Charles Spaniel	52	50	55	46	51
Cocker Spaniel	63	58	66	66	44
Doberman	18	17	19	18	51
Jack Russell terrier	61	58	60	54	45
Labrador Retriever	153	136	155	155	46
Miniature Dachshund	39	37	40	39	47
Miniature Schnauzer	32	29	31	29	49
Samoyed	41	40	84	74	50
Springer Spaniel	22	21	25	25	48
Staffordshire Bull terrier	15	14	15	15	52
Tibetan terrier	30	30	30	30	51
West Highland White terrier	135	123	135	129	45
Yorkshire terrier	79	76	80	75	47
Total	922	859	979	927

The SNPs used in the analyses are shown in Table 3 of the research study but for this paper summary purposes are omitted

Table 3

Genes and SNPs used in the study and type of human monogenic diabetes that has been associated with the gene

PNDM: Permanent neonatal diabetes; TNDM: Transient neonatal diabetes; MODY: Maturity onset diabetes of the young.

Findings and Results: [Genotype analysis revealed a significant association with all of the SNPs identified above. In the Bichon Friese, the ‘T’ allele of SNP rs23901704 was associated with reduced risk for diabetes, with the TT and TC genotypes being found in 4.8% and 38.1% of the controls respectively. These two genotypes were not found in any of the cases, where all the diabetic dogs of this breed carried the CC genotype compared to 57.1% of the controls. In the Samoyed, the ‘C’ allele of SNP rs23892119 was associated with increased risk for diabetes and represented 11% of the case population alleles; this allele was not found in the controls. For the genotype frequencies, the ‘C’ allele was found in only a small proportion of the case population with the TC and CC genotypes representing only 11.4% and 5.7%, respectively. The TT genotype represented 100% of the control genotypes and 82.9% of the case genotypes. The ‘G’ allele of SNP rs8804236 was associated with diabetes in the Miniature Dachshund. It represented 14% of the case alleles and 36% of the control alleles and the GG homozygous genotype was more common in the control population (29.6%) than in the cases (2.7%). The GA heterozygous genotype was more common in the cases (21.6%) than the controls (3.8%); the AA homozygous genotype represented 75.5% and 69.2% of the cases and controls respectively. Three SNPs were associated with diabetes in the Cocker Spaniel breed. For SNPs rs22302353 and rs22686871, the major allele homozygote (GG and TT respectively) was more common in the cases than the controls and for rs22686871, it represented 100% of the case genotypes, compared to 78.5% of the controls. For SNP rs24305581, the minor allele (‘A’) was found in 69.7% of the case genotypes (AA+AG) vs. 39.4% of the control genotypes and the GG genotype was more common in the controls (60.6%) than the cases (29.3%). The heterozygous genotype for this SNP represented more than 50% of the case genotypes but only 33.3% of the control genotypes. Analysis of genotype combinations across these three associated markers in this breed did not identify any genotype combinations that were more or less common in either the case or the control populations, indicating that the associations are independent of each other (data not shown).]

The conclusion drawn from this study indicates that some of the canine diabetes share similar factors with monogenic forms of human diabetes, the type known as maturity onset diabetes of the young (MODY). However, there is no conclusive evidence of monogenic diabetes association studies in dogs. The study identified 6 canine allelic associations to genes that align with MODY. None of the allelic groups can explain diabetes risk in any given breed. One gene (ZFP57) was associated with two different SNPs in the Bichon and Samoyed. Three genes (MTTL1, PAX4, INS) from 3 SNPs has association within the Cocker Spaniel breed. The same allele (C) occurrences were also found for both controls and cases in “the Border collie (0.2 and 0.17), Labrador (0.17 vs. 0.22), Miniature schnauzer (0.36 vs. 0.34), Samoyed (0.15 vs. 0.17) Springer Spaniel (0.08 vs. 0.12), West Highland white terrier (0.16 vs. 0.18) and Yorkshire terrier (0.09 vs. 0.06)”. Similar trends are seen for the other associated SNPs in the different breeds types.

It suggests that the allele and genotype occurrences do not specify 100% susceptibility to canine breed-related diabetes. It does however propose that canine diabetes is a polygenic trait with multiple genes conferring susceptibility. Lastly, it also advocates both forms in that a proportion of the dogs within a breed have a monogenic form of diabetes and that the remainder of the breed have a polygenic ( Polygenic inheritance occurs when one characteristic is controlled by two or more genes) form of the condition. Further studies and investigations are required.

The underlying aetiology and pathogenesis of canine diabetes have not been fully established and while insulin deficiency is a consistent feature, it remains a heterogeneous condition. The presence of specific breed predispositions and phenotypes within breeds suggests an underlying genetic basis for diabetes susceptibility but this susceptibility varies between breeds and is likely to result from the interactions of multiple genes.

Amongst the hundreds of research studies currently out there it is still difficult to pinpoint the root cause for such an obscure disease. Is this disease Monogenic, Polygenic? Can one single gene, two multiple genes or a mutation of a single gene give way to express onset? For now, there is no cure and no sound conclusive analytical models that can be utilized to defend. There are many genetic and morphology factors which could play a role in these uncertain study prognoses. Based on some of the conclusive research quoted above it is concerning to note that a single gene mutation, carried from neither parent could wave to onset. In theory, and bearing in mind when breeding dogs, it would be important to take serious consideration whether to utilize frozen semen (a vector of unknown genetic modification), and or possibly breeding dogs of older years.

“Etiology and Pathophysiology: Leaky gut and diabetes mellitus: what is the link?”: S. de Kort, D. Keszthelyi and A. A. M. Masclee; October 2010, University Medical Center, Massstrict, the Netherlands.