1

Genetics and preventing

syringomyelia Genetics

2

Inheritance of SM

• Moderately high hereditability

– SM = 0.37 (maximum is 0.64)

• What does that mean?

– Complex inheritance involving >1gene.

• ? genes at two or more loci interact to give disease

– Expression of disease may be influenced by

other as yet unknown factors

– There is a good chance of “breeding it out”

Heritability of syringomyelia in Cavalier King Charles Spaniels.

Tom Lewis, Clare Rusbridge, Penny Knowler, Sarah Blott, John A. Woolliams.

Vet J. 2009; 183 (2010) 345–347.

Inherited CMSM in humans

• Tartar population

• Typical appearance

– Brachycephalic

– Short neck

• Variation in presentation and

progression

– Large syrinx progresses quicker

– Mild cases may be asymptomatic

– Some resolve (syrinx bursts)

• Genome work in progress

• Work of Enver Bogdanov

(Kazan Tartarstan)

3

Canine CM/SM genome project

- 2 parts

Search for

syringomyelia genes in

Cavaliers

Search for chiari

genes in Griffon

Bruxellois

Cavalier having

a DNA sample

taken after a

MRI scan

(saliva sponges)

4

Results - GWAS GB CM

• 2 candidate loci (i.e. small areas of a chromosome)

GWAS results obtained from a Canine SNP20 BeadChip

The loci are in order from the strongest P value to the weakest.

The red line represent the bonferroni threshold. (i.e. statistical significance)

Fine mapping – CKCS SM

Linkage disequilibrium in fine-mapping region

analyzed by Haploview v4.2 with R squared method

10-SNP window spans 1.3 Mb.

Block 1 P value = 3,2 x 10-15

red triangle indicates significant region on the chromosome

5

Preventing - Syringomyelia

the iceberg effect

Clinical cases

Subclinical cases –

offspring can be

clinically affected

Unaffected dogs

Iceberg Picture

Ralph Clevenger

Why MRI

screening of

breeding stock

is currently so

important

Prevention of CM/SM 2004-2011

• MRI screening of breeding stock

• Breeding guidelines

– Eliminate early onset SM dogs (E)

– Only breed young clear (C) to older clear (A)

– Only breed late onset SM (D) to older clear (A)

– Identify CM free dogs?

6

Breeding Guidelines - CMSM

7

Breeding guidelines

4 year results

8

KC / BVA CMSM MRI Scheme Proposed KC/BVA CMSM scheme

AIM

• Quality control

– minimum standard for MRI

– Interpretation by qualified & experienced panel

– Eliminate problem of inaccurate results due to

substandard MRI scanning or interpretation

• EBV

– Computerised mate select program

– Empower breeders

• improve breed health

• maintain genetic diversity

9

Images required

• Sagittal T1W – interthalamic adhesion to at least to C4/C5

– maximum slice thickness 4mm

– Dog must be positioned “straight”

• Sagittal T2W

• Transverse T1W or T2W images – perpendicular to the spinal cord through

• the maximum width of the syrinx if SM is present

or

• block centered on C3 , extending mid C2 to mid C4

How are the images graded?

• Severity of CM

• Severity of SM

• Age at time of scanning

10

Chiari-like malformation (CM)

Grade 0 - No Chiari malformation

Grade 1 - Cerebellum indented (not rounded)

Grade 2 - Cerebellum impacted into, or

herniated through, the foramen magnum.

Proposed KC/BVA scheme

• Grade 0, no CM – the cerebellum has a rounded

shape with signal consistent with cerebrospinal fluid

(CSF) between the caudal cerebellar vermis and the

foramen magnum

0 of 564 (0%) breeding CKCS

reported by CR in previous 24 m

11

Proposed KC/BVA scheme

• Grade 1 CM – the cerebellum does not have a rounded

shape, i.e. there is indentation by the supraoccipital bone, but there

is a signal consistent with CSF between the caudal vermis and the

foramen magnum.

6 of 564 (1.1%) breeding CKCS

reported by CR in 24 m period (previously reported as “mild”)

Proposed KC/BVA scheme

• Grade 2 CM – the cerebellar vermis is impacted

into or herniated through the foramen magnum.

558 of 564 (98.9%) breeding

CKCS reported by CR in previous 24 m

12

Chiari-like malformation

Which dog will get SM ?

8 months

8 years

Overcrowding of the FM large cerebellar herniation not required

Be cautious before declaring a dog safe to

breed on the basis of appearance of the brain

Proposed KC/BVA scheme

Syringomyelia grades

• Grade 0, normal

– (a = over 5y; b = 3-5y; c = 1- 2.9 y)

• Grade 1, CCD < 2mm

– (a = over 5y; b = 3-5y; c = 1- 2.9 y)

• Grade 2, SM or pre-SM or CCD ≥ 2mm

– (a = over 5y; b = 3-5y; c = 1- 2.9 y)

13

Parker J. et al 2010

Why has “cut off” changed to 3y?

Prevalence of SM in asymptomatic CKCS

Central canal dilatation

14

Pre-syrinx i.e. oedema may only be seen on T2W images

Proposed new guidelines

Age SM grade

0a 0b 0c 1a 1b 1c 2a 2b 2c

No

rmal >5 0a yes yes yes yes yes yes yes yes

DO

NO

T B

RE

ED

3-5 0b yes yes yes yes

1-3 0c yes yes yes

CC

D >5 1a yes yes yes yes yes yes yes yes

3-5 1b yes yes

1-3 1c yes yes

SM

>5 2a yes yes

3-5 2b yes yes

1-3 2c DO NOT BREED

Dog with clinical

signs CM &/or SM DO NOT BREED

15

Mate select program (EBV) The need for estimated

breeding values !

16

Conversation with breeder

• “I am worried about using ……Dog X who

was …. scanned A but …..has fathered

several progeny with SM”

• Only the vet and breeder of Dog X know

that when younger Dog X was indeed an

A … however since rescanned and is a D

• The results of Dog X are confidential - i.e.

vet cannot comment

• The breeder of Dog X keeps quiet

• EBV will help to protect breeders

Thanks to..

Tania Ledger for the cartoons!

17

Acknowledgments Funding Canadian Institutes of Health Research

Syringomyelia DNA research

For the Love of Ollie fund Rupert’s Fund & Friends of Lola Fund

Cavalier Friends

UK CKCS & Griffon Bruxellois clubs DNA archive for Companion Animals Manchester

Marshfield Clinic (NIH)

Ann Conroy Trust

American Kennel Club Health Foundation CKCS club of USA Health Foundation

The Cavalier Club of the Rand

French Cavalier Club Cavalier Club of Canada

Frank and Lee Pieterse

Also indebted to……. Stone Lion Veterinary Hospital Margaret Carter, Tissue Collection Scheme Lee Pieterse Carol Fowler, Tania Ledger, Cavalier Matters Dana Schuller-Kuyper Rachel Harvey, Maria Oliver, Henny Van den Berg Diaconessenhuis Meppel CMSM screening program Paul Mandigers and Utrecht University Giunio Bruto Cherubini, Dick White Referrals Holger Volk, Colin Driver and RVC Simon Platt and Georgia University Natasha Olby and North Caroline State University Nick Jeffrey, John Parker and Cambridge University

Genome Project

SM project

Vincent Quoc-Huy Trinh

CM project

Philippe Lemay

Overseen by Zoha Kibar

Guy Roleau

Penny Knowler

Clare Rusbridge

Greatly assisted by Alexandra Thibault

Karine Lachapelle

Annie Levert

Daniel Rochefort

Melanie Benard

Isabelle Thibault

Claude Marineau

Yan Yang

Statistical analysis

Marie-Pierre Dube

Sarah Blott

Sylvie Provost

Thanks for listening…..

Any questions??

18

Getting the best from your

MRI for imaging CMSM Aim

• Obtain diagnostic images

• Economical for cost and time

19

“General anaesthesia, narcosis

or deep sedation required”

General Anaesthesia

• Dexdomitor & butorphanol premedication

• Propofol induction

• Isoflurane & oxygen

maintenance

Labelling dicom images

20

Positioning

The dog’s head and neck should be in full extension so that the skull base is in

line with the floor of the vertebral canal through C1 and C2

To flex or not to flex ?

Atlantoaxial subluxation; CKCS

21

Get as straight as possible

• Positioning of dog

• Dorsal & transverse localisers (30 secs)

Cisterna magna to C4/C5 IVD must be

continuously visible in a single sagittal image.

22

What if despite everything the head is squint? Separate imaging of the brain

23

May under-estimate CM Transverse images – obtain

though areas of pathology

24

Common faults Poor quality images

Only sequence submitted

25

Poor quality images

Shortcuts will miss subtle

pathology!

26

Wrong sequences / area

Poor quality (especially

of spinal cord) and only

imaged to C2/C3

Better quality but cannot

visualise large syrinx in

spinal cord

Wrong sequences

27

Correct positioning and images Microchip artefact

28

Microchip artefact

Scoliosis