BOXER UpdateA NESTLÉ PURINA PUBLICATION DEDICATED TO BOXER ENTHUSIASTS VOLUME 15 | FALL 2017

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When their 9-year-old brindle Boxer“Lyric” (CH LattaLane’s Irish Lyric)showed early-stage degenerativemyelopathy (DM) in the spring of2015, breeders Thomas J. and CarolLatta of Corder, Missouri, alreadyrecognized the signs. They hadbeen screening their breedingBoxers for DM since the genetictest became available in 2009.

Not surprisingly, given the preva-lence of DM in the breed, everyBoxer in their breeding programhad tested at risk for DM. However,Lyric was their first, and thus faronly, Boxer affected by the disease.

Fifty-seven percent of Boxers areconsidered at risk for DM, rankingthe breed among those deemedhighly susceptible to the late-onsetprogressive neurodegenerativedisease. First recognized in GermanShepherd Dogs in the 1970s, thedisease affects nearly 30 breedsplus mixed breeds. Adult dogs areusually around 9 years old whenthey develop DM.

A difficult disease to diagnosesince it mimics other conditions,veterinarians rule out other diseasesbefore determining if a dog has DM.A diagnosis is expensive because it

BOXERS WITH DEGENERATIVE MYELOPATHY

Fall 2017

MAY BENEFIT FROM DIAGNOSTIC BIOMARKER TEST

FIFTY-SEVEN PERCENT OF

BOXERS ARE CONSIDERED

AT RISK FOR DEGENERATIVE

MYELOPATHY, RANKING

THE BREED AMONG

THOSE DEEMED HIGHLY

SUSCEPTIBLE TO THE

LATE-ONSET PROGRESSIVE

NEURODEGENERATIVE

DISEASE.

requires an MRI (magnetic resonanceimaging) of the spinal cord. Eventhen, it is considered a presumptivediagnosis, as a definitive diagnosisis not possible until a dog dies anda necropsy and histopatholgy areperformed.

Dragging or scuffing the hind legsis the first sign owners notice. Decreas-ing muscle control and weaknessin the rear limbs lead to frequentfalls and difficulty getting up. Usuallywithin 11 months, a dog is paralyzed.The progressive disease spreadsthrough the central nervous system,damaging the spinal cord, muscles,nerves, and brain.

“We began to notice that Lyric’srear paws occasionally knuckled overwhen she walked,” says Thomas Latta.“A DM clinical trial was underway at the University of Missouri, so wecontacted them to see if Lyric couldtake part because we live only anhour away and would be able tomake the required checkup visits.”

Lyric was accepted into a clinicaltrial designed to test a new therapyfor the condition.

A PROGRESSIVE DISEASEDM affects axons, as well as reduces

the nerve insulation, or myelin inneuronal fibers. The process hinderssignal transmission, resulting inhind limb clumsiness and loss ofmobility. When the nervous sys-tem is no longer able to transmitsecondary information or motorcommands between the brain andhind limbs, a dog loses completemuscle function.

“The disease progresses to affectthe front limbs, and then dogs go allthe way down to where they areunable to walk and have difficultyswallowing as the brain stem becomesaffected," says Joan R. Coates, DVM,DACVIM-Neurology, professor ofneurology and neurosurgery at theUniversity of Missouri. “It progressesfrom a disease that a neurologistwould localize to the spinal cord to onethat affects nerve and muscle function.”

A longtime researcher of DM,Dr. Coates led the discovery in2009 of the autosomal recessive

gene mutation in the superoxidedismutase (SOD1) gene. This research, which was done in collab-oration with the Broad Institute ofMIT and Harvard and Gary Johnson,DVM, PhD, of the University ofMissouri, found that the mutationresponsible for DM in dogs is thesame mutation that causes ALS(amyotrophic lateral sclerosis), orLou Gehrig’s disease, in humans.

ALS is named for the New YorkYankee’s Hall of Fame first basemanwhose 16-year major league baseballcareer ended in 1939 due to ALS andwho died from the disease in 1942.Knowing that DM and ALS are relatedled Dr. Coates and her team to begininvestigating whether the diagnos-tics used in treating ALS patientsalso could be used for dogs with DM.

In Boxers, the DM allele frequencyis 72 percent, meaning that themutated gene is found on 72 per-cent of chromosomes carrying thealleles. To be affected, a Boxer mustinherit a copy of the gene mutationfrom its sire and dam, though tobe a carrier, only one copy of themutation is needed.

Although the DNA test helpsbreeders make prudent breedingdecisions, it has diagnostic limita-tions. Results from genetic testingallow breeders to breed dogs thatcarry the SOD1 gene mutation toclear, healthy dogs to avoid produc-ing affected dogs without reducinggenetic diversity.

Dr. Coates also is the principalinvestigator of research leading tothe recent discovery of a diagnos-tic biomarker that can be used toidentify dogs at risk for develop ingDM. This research, published in theMarch-April 2017 issue of the Journalof Veterinary Internal Medicine,found that in dogs with DM, asin humans with ALS, a structuralprotein of motor axons containedin cerebrospinal fluid increasescompared to older normal dogsand dogs with other mimickingspinal cord diseases.

This finding promises to help inthe early diagnosis of DM. Meanwhile,two clinical trials at the University

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BOXER Update

SIGNS OF DEGENERATIVEMYELOPATHY• Dragging or scuffing the hind legs• Incoordination• Decreasing muscle control• Weakness in rear limbs leading to

frequent falls• Difficulty swallowing• Paralysis

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Fall 2017

of Missouri are evaluating effectivetherapies for dogs with DM. The onein which Lyric took part is a study tolearn how injections of antisenseoligonucleotides (ASO) slow theprogression of disease. The other isa gene therapy study. Both therapiesaim to suppress the SOD1 proteinproduction. Here is a review of therecent progress to better under-stand DM.

THE pNF-H BIOMARKERThe ability to diagnose dogs with

DM early in the disease process usingthe biomarker test will be helpful oneday when there are effective ther-apies to help improve quality of lifeand life span. Working with Dr. Coateson the biomarker research wereMichael Garcia, PhD, co-principalinvestigator and a graduate studentin the Department of Biologic Sci-ences, and Christine Toedelbusch,DVM, a veterinary neurology resi-dent and doctorate candidate. Theresearch was funded by the AKC(American Kennel Club) CanineHealth Foundation and the AmericanBoxer Charitable Foundation.

In humans with ALS, an abundantstructural protein found in the mye li -nated motor axons of nerve cells,called phosphorylated neurofilamentheavy (pNF-H), was shown to haveincreased concentrations in bloodand cerebrospinal fluid that aid indiagnosing the disease. The releaseof this protein occurs due to the degen-eration of neural tissue and axons.

Based on this information, theresearch team began investigatingwhether this is true for dogs as well.“We hypothesized that pNF-H isreadily detectable in the cerebro spinalfluid and blood of DM-affected dogsand thus could be a diagnostic bio-marker for DM,” explains Dr. Coates.“We found, however, that DM-affected dogs have higher levels of pNF-H in cerebrospinal fluid butnot in their blood.”

The study involved evaluating thecerebrospinal fluid and blood of DM-affected dogs, those with a confirmeddiagnosis and those in the early stage

of disease, as well as neurologicallynormal dogs, dogs with diseasesthat mimic DM, and asymptomaticdogs considered at risk for DM.

“Collecting cerebrospinal fluid ismore complicated than collectingblood because it requires anesthesia,but it is less expensive than an MRI,”Dr. Coates says.

The study showed that the bio-marker test used to diagnose humanswith ALS also can be used to diag -nose dogs with DM. “As this testbecomes more accessible to veteri-narians and is used more frequently,it is possible we will begin to seereliable DM diagnoses from spinalfluid samples,” says Dr. Coates.

EFFECTIVE THERAPIESThe two DM clinical trials underway

at the University of Missouri have thesame goal: to suppress the SOD1protein production and thereby helptreat affected dogs. One involves amolecular approach, and the otherrelies on gene therapy to help treatthe disease.

“Part of the challenge in treatingdiseases of the central nervoussystem is getting past the blood-brain barrier, the protective barrierthat separates the brain from thecirculatory system, so the treatmentcan get into the spinal fluid andnervous tissue,” Dr. Coates says.

The idea behind the molecularapproach, or ASO therapy, is todisrupt the coding for SOD1 byusing short strands of syntheticDNA as therapeutic agents. Thetheory is that ASO injections containing synthesized strands of nucleic acid will bind to themessenger RNA produced by thegene to silence it. A parallel studyis underway in humans with SOD1-associated ALS.

“When ASO is injected into dogsor people, it suppresses the codingfor SOD1 protein, thereby slowing orpossibly halting the disease progres-sion,” explains Dr. Coates. “We wantto define how long the ASO drugstays in the spinal fluid cells to helpdetermine the frequency of injections.”

BOXER OWNERS CANPARTICIPATE IN DM CLINICAL TRIALS

Owners of Boxers may help advanceresearch of degenerative myelopathy(DM) by participating in clinical trialsunderway at the University of Missouri.The research team has two ongoingstudies in which they are seekingBoxers 9 years of age and older whendiagnosed. For additional information,you can visit the University of Missouriwebsite or email lead investigator Dr. Joan Coates.

To qualify, a dog must be healthyand early in the disease process asconfirmed by a board-certified vet-erinary neurologist. Owners mustagree to return to the university forfollow-up examinations.

Here is the criteria to participate:• Slow, progressive loss of coordina-

tion over one to three months andnot in discomfort

• Diagnostic testing showing no significant abnormalities on bloodwork, thoracic radiographs or abdominal ultrasound

• Normal spinal cord MRI (magneticresonance imaging)

• Normal cerebrospinal fluid analysis• Normal electrodiagnostic testing • Genetic results showing homozygous

for the SOD1 gene mutation

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BOXER Update

The ASO study in dogs is fundedby the National Institute of Neuro-logical Disorders and Stroke, whichis part of the National Institutes ofHealth, the AKC Canine HealthFoundation, and the AmericanBoxer Charitable Foundation.

Meanwhile, the gene therapyclinical trial involves using a smallsequence of iRNA, or interferenceRNA, to suppress SOD1 protein pro-duction. This study, which is fundedby the ALS Association TREAT ALS,TM

involves giving dogs a one-time injection into their spinal fluid, withfollow-up appointments in one monthand then every three months.

MAKING STEADY PROGRESSLyric participated in the ASO clin-

ical trial for 18 months. In December2016, there was an unexpectedchange in her condition.

“We took Lyric to Dr. Coatesand made the painful decision tosay goodbye to our sweet girl,”Thomas Latta says. “Although DM

had affected her quality of life, inthe end it was hemangiosarcomathat took her life.”

Progress in treating and under-standing DM is slow but steady.“The DNA test gives breeders achoice and aids their breedingprogram,” says Dr. Coates. “Thesetherapeutic treatments we are investigating are important, too, asis the ability to diagnose affecteddogs early. DM is a heartbreakingdisease, but one in which I am optimistic that we can have an impact in helping affected dogs andthose who love them, and alongthe way help progress the clinicaltrial studies in ALS patients.” �

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Purina thanks Dr. Joyce Campbell, chairof the American Boxer Club Health andResearch Committee and a trustee ofthe American Boxer Charitable Founda-tion, for helping us to identify this topicfor the Boxer Update.