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An Overview of Ehlers-Danlos Syndrome (Cutaneous Asthenia) in the Feline

3505 words (14 pages) Essay in Biology

08/02/20 Biology Reference this

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Abstract

Ehlers-Danlos syndrome is a group of heritable tissue disorders caused by collagen deficiency in man.  The condition is more generalized in the feline despite the recent relation of similarities of the syndrome in man.  Its presentation is that of hyperextensible skin, easy occurring wounds with an extended healing time, and laxity of joints in some cases.  Its rare occurrence has limited man’s knowledge of the disease in both species.  This paper will provide a background for the syndrome, the clinical presentation, the course of diagnosis, and treatments in use, though no definitive or all-inclusive treatments exist.  Its existence is based on genetics factors that vary.  These factors collectively comprise a group of disorders that affect collagen production, some restricting the amount of normal collagen produced and some affecting the quality of the collagen that ultimately bundles and strengthens the skin and joints.  Speculation has been a large part in the cause of this disorder, but recently researchers have identified an impressive correlation between the presence of a mutation within a gene also common to man.  A stronger focus on the disorder may lead to more direct and effective testing in regards to the feline, limiting the course of testing involved.  There is no definitive treatment for this disorder, although the relationships shown between man and feline with this disorder may lead to more rapid discoveries in the syndrome that can benefit man and feline. 

Introduction

Ehlers-Danlos Syndrome (EDS) is a disorder labeled more commonly in man.  The syndrome appears similarly in other animals such as cats, but is documented under other names such as cutaneous asthenia or dermatosparaxis, a term previously coined to describe the medical occurrence.  There are 13 classified subtypes of EDS documented in man.  These are Classical EDS (cEDS), Classical-like EDS (clEDS), Cardiac-valvular EDS (cvEDS), Vascular EDS (vEDS), Hypermobile EDS, Arthrochalasia EDS (aEDS), Dermatosparaxis EDS (dEDS), Kyphoscoliotic EDS (kEDS), Brittle Cornea Syndrome (BCS), Spondylodysplastic EDS (spEDS), Musculocontractural EDS (mcEDS), Myopathic EDS (mEDS), and Periodontal EDS (pEDS) (The Types of EDS, n.d.).  Current reference to feline cases are simply documented under the term cutaneous asthenia.  Cutaneous refers to the integumentary system, while the word asthenia portrays a weakness or a loss of strength.  Cutaneous asthenia presents as abnormal elasticity of the skin due to a collagen defect.  Blood vessel damage may occur, as well as an increase in the time for typical wounds to heal (Boden, 2015).  Aside from the focus on the condition of the skin in the feline, other medical issues have occurred that correlate with the condition of cutaneous asthenia.  In a 2004 study of an 11 year old short hair cat, the authors described a hernia issue that was ongoing in a cat that was deemed to be suffering from the disorder (Benitah et al., 2004).  Most studies address the abnormal physical traits of the skin, despite the long list of subtypes existing in the man that may present a relation to that of those in the cat.  Because of phenotypic variability, diagnosis may present slight complication.  There is no simple testing for a case of cutaneous asthenia and diagnosis is dependent on several factors being evident.  Genetic discoveries have been made and compared to some of the human subtype conditions showing that our interest in this condition is currently growing, although genetic discoveries are lagging behind the physical discoveries in the feline.  Enzyme and amino acid breakdown is currently in identification, but more importantly we are seeking the genetic influence on the proteins that comprise these enzyme systems and why they are incorrectly assembled.  Fibrillary collagen is the major factor in the skin elasticity of cutaneous asthenia cases and the product of an incorrect assembly of a triple helical structure (Spycher et al., 2018).  It has no benefit in the feline species at this time.  This condition has no cures and treatments are limited.

Etiology

The research into Ehlers Danlos in man has far exceeded the research put into the feline disease, alternately known as cutaneous asthenia.  Information that we are now obtaining is being linked to similar disorders in man.  Classical EDS in man is found to be a product of changes in the COL5A genes.  While many other genes are suspected to be involved with abnormal collagen production, the forms are connected to dominant, recessive, and chromosome X mutations.  It would seem that the condition of the feline could arise from some of these similar anomalies.  A recent genetic investigation revealed that the COL5A1 gene of the feline is the location of a frameshift variant that is comparable to the COL5A1 gene in man.  The variant identified as COL5A1:c3420delG causes a premature stop codon that truncates a third of the 1837 amino acids that compose the protein.  The COL5A1 gene is 96% similar in comparison of amino acid composition to man and exhibits comparable variants.  During this investigation it is noted that parents were not available, and due to this the variant cannot be determined to be caused by a de novo mutation or transmission through ancestry.  The gene variant was not found to be similar to 104 other documented feline cases (Spycher et al., 2018).  The biochemical result of this variant is an NH2 procollagen peptidase which is deficient.  This deficiency leads to a processing error in precursor chains pNa1 and pNa2 which amounts to a buildup of these precursors in the skin.  Skin affected by this error in collagen synthesis maintains the same amount of collagen but quality is concern (Counts et al., 1980). 

When narrowing in on a Himalayan cat suspected to suffer from the condition, it was recognized that a portion of the collagen was synthesized in a normal fashion, but nevertheless the visibility by transmission and electron microscope of the abnormal collagen molecules exhibits a failure to integrate into fiber bundles that are networked in the dermis of the skin (Holbrook et al., 1980).  The failure to integrate causes the defect in skin and in some cases joint laxity may be observed.  In severe cases, frequent luxation may occur with joint laxity (Corina & Elefterescue, 2007).

Researchers reviewed the cases of several Burmese cats and note that there is an increased prevalence of this condition witnessed in Australia.  It is not known if there is a link to the condition through ancestry or if the increased numbers of cases are due to this breed of cat being predominant in the choice of pet (Hansen et al., 2015, Spreyer et al., 2015).  Within the studies supporting this paper, it is noted that a variety of cats were identified as suffering from the syndrome.  No restrictions were made or found, although some background history of the subjects are missing. 

Clinical Exam & Diagnosis

The process of correctly diagnosing a cutaneous asthenia cat requires many laboratory methods that often are not employed until a later date because the syndrome is rare.  In the first known feline case in the country of Turkey, a 2 year old cat was admitted and described as suffering from anorexia, alopecia, and hyperelasticity of the skin.  Upon further examination the subject was found to have generalized lymphoadenopathy, and ulcerative wound, and hyperextensibility was confirmed when a skin extensibility index (SEI) was conducted.  During blood count, mild leukocytosis and hypoproteinemia was evident.  Urea nitrogen levels were also find to be slightly higher than normal.   To rule out other more probable agents of the symptoms, feline leukemia virus (FeLV), feline immunodeficiency virus (FIV), and feline infectious peritonitis (FIP) testing was completed. Urinalysis results revealed no abnormalities.  Using spectrophotometry, the condition of alopecia was investigated further and it was found that the content of zinc was lower than the typical range.

Furthering their attempt to finalize the diagnosis, a biopsy was performed and sent for histopathological examination.  Skin scrapings and hair plucks were viewed for parasites and fungal infection.  Neither found.  During histopathology, skin samples were stained with hematoxylin and eosin (H&E) and Masson’s trichrome and examined with light microscopy.  H&E and Masson’s trichrome staining has had a limited benefit in the diagnosis of cutaneous asthenia (Fernandez et al., 1998, Sequiera et al., 1999).  In this case, histopathologically there was neutrophilic infiltration, fibrosis, and necrosis in between collagen fibers that was documented and in sections where Masson’s trichrome was applied.  Also, formations of fibroblasts were observed.  Fibrocytic and fibroblastic hyperplasia were existing below the epithelial layer with an increase in fibroblastic cells and collagen deficiency (Dokuzeylul et al., 2013).

In another case, a 1 year old Korean domestic short hair cat was evaluated and later determined to be suffering from the condition as well.  This cat also was found to be suffering from slow healing wounds and extensive skin elasticity.  With a complete blood cell count and serum biochemistry, moderate polycythemia, increased glucose, and decreased albumin was recognized.  After emergency treatment of the presenting lesion, bacteria culture and sensitivity test and histopathological tests were performed.  A skin scraping, fungal culture, and low dose dexamethasone suppression (LDDST) were also performed.  The results of this testing revealed a presence of fungal components, bacterial components, but a negative result for hyperadrenocorticism.  Histopathology revealed a wide separation of collagen bundles, inactive hair follicles, and macrophage infiltration.  In this case the diagnosis went toward cutaneous asthenia with complications from fungal and bacterial agents.  Because joint hypermobility was not seen in the initial exam and the cat’s age young, the researchers felt the cause may have been an autosomal recessive form of congenital cutaneous asthenia.  Researchers were not able to confirm any further information from testing because of the mixed breed, shelter adoption status of the cat (Seo et al., 2016).  

Treatment

Treatment in suspected cases of cutaneous asthenia is limited.  There is not a definitive cure at this time and treatments reflect a palliative care effort.  Prognosis is poor in extreme cases and may require the animal to be euthanized.  Prevention has become a large component of addressing the symptoms of the disorder.  With the weakness of skin, wounds occur more frequently and easily.  As mentioned before, healing processes are extended in duration.  The state of open wounds also increases the susceptibility of infections. 

Prevention is the primary means of treatment.  It is suggested that sharp items in the home be removed or padded in order for the cat to avoid injuries.  Another consideration is an upkeep on flea medications to eliminate cases of pruritis due to avoidable parasites.  Despite the detrimental effects of declawing a cat, in the case of cutaneous asthenia the benefits may outweigh the risks.  Lacerations and hernias must be addressed immediately as they occur (Hnilica et al., 2017).   

Common suggestion for treatment in some studies is the supplementation of Vitamin C (Paterson, 2000, Scott et al., 2001).  Vitamin C acts as prerequisite for the formation of collagen.  It is required with other cofactors that aid in the hydroxylation of the proline in collagen synthesis from a substrate.  Ascorbate enhances endothelial synthesis and deposition of Type IV collagen that comprises the basement membrane of blood vessels.  Plasma ascorbate is delivered via a vascular tree to the necessary organs (May & Harrison, 2013).  When there is deficiency in the bioavailability of Vitamin C, there are many skin issues that may arise but collagen abnormalities are the most prevalently known.  While the supplementation of Vitamin C in one cat seemed to alleviate the severity of the syndrome, it has not yet been proven to aid in the treatment of cutaneous asthenia (Szczepanik et al., 2006).

When referring back to the case from Turkey, the team treated initially with saline intravenously (IV), ceftriaxone disodium, dexpanthenol, vitamin C, and vitamin E for 10 days.  Cephtriaxone is an employed as an antibiotic and dexpanthenol acting as a precursor to acetyl CoA.  At 10 days the blood was redrawn and leukocytosis was found to be reduced and total protein levels were within range.  Skin elasticity remained the same.  The treatment protocol was continued with vitamin C, E, and zinc.  Collagen was also added to the diet of the cat.  The owners were instructed to continue this regimen for the next six months and no additional issues were reported within this time (Dokuzeylul et al., 2013).

In the case of the Korean short hair, treatment included addressing the underlying components.  Itraconazole and amikacin were implemented for effect upon the fungal and bacterial components.  After 30 days, skin issues were remarkably lessened but the SEI still revealed a hyperextensibility of the skin.

Outcome for the 6 month old Himalayan cat included a survival had surpassed 2 years after the diagnosis of cutaneous asthenia.  No treatment was described for this case.  These cases owe to the fact that cutaneous asthenia does not always require the patient to be euthanized.  Most cases can be addressed using prevention techniques (Holbrook et al., 1980).

 In cases where joint laxity is an issue lameness may occur.  It is said that there does not appear to be pain but this condition poses a negative outcome (Ehlers-Danlos Syndrome, n.d.).  Since there is no cure or definitive treatment for this syndrome it is advised that previously diagnosed animals refrain from breeding.

Conclusion

Ehlers Danlos studies in cats may provide much insight into the future studies of man.  The presence of similarities are already being distinguished, as seen in the relative cases of the genetic cause of cutaneous asthenia in the cat and cEDS in man.  The syndrome has been very much generalized in the feline up until this point and mostly described from a phenotypic point of view.  The COL5A1 gene relationship recently presented between the feline and man may provide the interest needed to continue the research in regards to the disorder.  Collagen deficiency remains the cause of this disorder in both species. Clinical diagnosis is subject to a battery of testing because of a lack of direct testing for this issue.  Abnormal ranges of blood cell counts and other testing may be caused by secondary factors such as the opportunity for infection once a wound is established.  Definitive diagnosis comes from intense microscopy and biochemical testing.  Our diagnosis using these techniques is a knowledge that exceeds our genetic knowledge.  With an abundance of subtypes in the man, the further study of the feline should be carried out.  It is possible that the generalized condition that have labeled for the cat carries its own subtypes.  The identification of further subtypes would add to the knowledge that we have invested in these studies so far in man.  While these cases have been documented in several breeds such as Himalayans, a Korean short hair, and Burmese cats, the only segregation seems to be represented within the Burmese cats.  It is these cats that could provide an interesting look into the genetic basis of this disease.  It could also further the knowledge of the clinical and biochemical properties of the syndrome.  Perfecting a testing technique for suspected cutaneous asthenia could allow us to avoid the intensive testing and research that is required in identification of this syndrome in the typical cat.  Extensive testing can be expensive and time consuming, a deterrent to the pet’s owner and troublesome for an owner already dealing with the ongoing symptoms of the syndrome itself.  After expense, treatment is still limited with no guarantees.  This problem similarly presents itself in man despite extensive studies.  With a proper diagnosis and prevention of the cat from inflicting harm upon itself, there is a fair prognosis for these cats.  Cats that are euthanized are often suffering from a severe form that will not decrease in intensity.  These cats may suffer from poorly healing wounds or severe luxation of joints.  Research in this field should be furthered to benefit both the feline and man in the reduction of suffering. 

 

References

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