For breeding advice, please scroll down, or click here to jump to the appropriate section.
What is CM/SM?
Chiari-like malformation (CM) is a fault in the development of the skull, causing part of the brain to protrude from the opening at the back of the skull. Syringomyelia (SM) refers to the presence of one or more fluid-filled pockets that may develop in the spinal cord, called syrinxes.
Although some dogs with mild CM/ SM can seem completely normal, other dogs experience intense pain and may be unable, or unwilling, to exercise and have increased sensitivity to touch, especially around the head, neck, shoulders and sternum (breast bone). Severe cases may show a characteristic shoulder, neck and/ or head scratching where they ‘air-scratch’ without making contact with the body. Some dogs show neurological signs such as incoordination and weakness.
How is CM/SM inherited?
Both CM and SM are complex inherited disorders, which are thought to be influenced by a number of different genes and possibly by environmental factors (i.e. diet, exercise or factors when in the womb before birth etc.). Each of the genes that help influence whether a dog develops CM/SM may have different possible versions, or variants. Some versions increase the risk of CM/SM, while others decrease the risk. Each dog will have a mix of these “good” and “bad” versions of genes, making it very difficult to predict whether a dog will be symptomatically affected. Screening for CM/SM before breeding is particularly important as some dogs do not show clinical signs but may still have CM/SM, and if used for breeding could pass on increased risk genes which cause symptomatic CM/SM in offspring. The impact one version of a gene has might only be slight, but lots of genes having a small influence have a combined additive effect. The way in which these conditions are inherited is not straight forward; hence the name complex inherited disorders. These complex diseases are usually seen across many different breeds and are also described in both cross breeds and mixed breeds.
Which breeds are affected by CM/SM?
There are a number of breeds where the conditions are known to occur. These breeds include: Affenpinschers, Cavalier King Charles Spaniels, Chihuahuas, Griffon Bruxellois, Havanese, King Charles Spaniels, Maltese, Papillons, Pomeranians, Toy breed crosses, Yorkshire Terriers, and rarely in Boston Terriers and Staffordshire Bull Terriers.
Is this scheme relevant to my breed?
Find out which health tests or schemes are recommended for your breed on the Kennel Club’s Breed Information Centre. These recommendations are suggested by breed clubs and approved by Kennel Club committees.
How can I get my dog graded for CM/SM?
The current BVA (British Veterinary Association) /Kennel Club scoring scheme for CM/SM was launched in 2012. The aim of the Scheme is to reduce or eliminate the incidence of inherited CM and SM in dogs by providing breeders with accurate information on the degree to which their dogs may be affected. It requires a magnetic resonance imaging (MRI) examination of the brain and upper neck. Although it is expected that the majority of dogs using the CM/SM Scheme will be pedigree toy breeds, the Scheme is open to all dogs, including crossbreeds.
Since CM/SM is a condition that develops and worsens over time, scans throughout the dog's lifetime are recommended, generally at year one, three to five years and over five years. There are a number of veterinary centres which offer MRI scanning facilities and which follow the protocol recommended by the Scheme to ensure an adequate quality of the images. The veterinary centre then sends the MRI images to the British Veterinary Association where they are examined and "graded" by a panel of neurologists and radiologists. Once the MRI images have been graded, the result is returned to the vet, who relates it to the owner, and a copy is sent to the Kennel Club for recording and publication.
Why screen your dog?
Breeders are able to test their breeding stock for CM/SM before the dogs are used for breeding. Testing all potential breeding stock, where relevant, allows breeders to better understand the kind of genes a dog may pass on to its offspring, giving them the information required to attempt to avoid producing affected puppies. Making informed decisions from health test results enables breeders to adapt their breeding programmes and reduce the risk of the diseases appearing in future generations.
What are the grades a dog may receive?
Chiari-like malformation (CM)
- Grade 0—No Chiari malformation
- Grade 1—Cerebellum indented (not rounded)
- Grade 2—Cerebellum impacted into, or herniated through the opening at the rear of the skull (the foramen magnum)
Dogs graded under the BVA/KC CM/SM scheme can have the following grades
- Grade 0—Normal (no central canal dilation, no presyrinx, no syrinx)
- Grade 1—Central canal dilation (CCD) less than 2mm in diameter
- Grade 2—Syringomyelia (central canal dilation which has an internal diameter of 2mm or greater), or separate syrinx, or pre-syrinx with or without central canal dilation.
The SM grade is also qualified with a letter indicating the age group at the time of scanning:
- a = more than five years of age
- b = three to five years of age
- c = one to three years of age
At the present time no specific breeding recommendations can be given for CM, but current best evidence suggests that there is a relationship between CM and SM, and that CM increases the risk of SM occurring.
The following breeding guidelines aim to remove dogs with early onset SM from the breeding programme and reduce the risk of future puppies developing SM. These are recommendations and the BVA and Kennel Club accept no liability for any breeding outcome.
The following table can be used to see which two graded dogs can be mated together. Please note that dogs with clinical signs (symptoms) of CM or SM should not be used for breeding.
Making balanced breeding decisions
As well as considering the implications of a dog’s CM/SM score, there are other important factors to consider when deciding whether two dogs should be mated together, such as temperament, genetic diversity, conformation, other available health test and screening results, the general health of the dogs, etc. Your breeding decisions should always be well balanced and take into consideration the qualities and compatibility of both the sire and dam that you are considering.
Can the results of the grading scheme be used to accurately predict if future puppies will be affected?
SM is a condition which is inherited in a complicated way not yet fully understood by scientists. Due to the complex nature of inheritance of SM, it is still possible that affected offspring may arise from parents which are clear from or are only mildly affected by SM. It is hoped that breeding appropriately from screened dogs will reduce the risk of producing affected offspring, but it must be stressed that this is not a guarantee.
Are the results published?
The names and results of Kennel Club registered dogs will be sent to the Kennel Club for recording on their database and will be made available:
- In the next available Breed Records Supplement
- On any new registration certificate issued for the dog
- On the registration certificates of any future progeny of the dog
- On the Health Test Results Finder in the Kennel Club's online health resource, Mate Select
What are the costs involved?
In addition to the charges levied by the veterinary centre associated with MRI imaging, the cost of having one dog graded under the scheme is currently £100.00 (inc VAT).
Number of Dogs
Charge per dog
Re-scoring / re-grading under appeal
Duplicate copy of certification
£25 per copy
£30 per copy
What is the anticipated turnaround?
Who reviews the MRI scans?
There is a panel of BVA-appointed neurologists and radiologists who will review the MRI scans. The MRI scans are assessed by two scrutineers who will agree the grading.
Where can I get more information on the scheme?
Free, detailed leaflets can be download here, or are available from either: Health & Breeder Services Department, The Kennel Club, Clarges St, Piccadilly, London W1J 8AB or the Canine Health Schemes Department, BVA, 7 Mansfield Street, London W1G 9NQ.
For further information on the schemes, please visit the BVA website.
Will CM/SM testing ever become mandatory for Kennel Club registration?
The issue of mandatory screening is not as black and white as it may appear. To read about the Kennel Club’s stance on mandatory health testing, please click here.
Will EBVs be available for CM/SM?
The Kennel Club urges more breeders to make use of the BVA/KC CM/SM health scheme, because it hopes the results can be used to develop Estimated Breeding Values (EBVs), which are much more accurate in determining the genetic risk that each dog will pass this complex and poorly understood condition onto its progeny. Data from the BVA/KC scheme can be linked to pedigree information, but requires that sufficient data is generated from health screening. This has already happened with BVA/KC hip and elbow schemes, but there are currently not enough data available, or dogs screened, to be able to create EBVs for CM/SM.
Will a DNA test for CM/SM be developed in the near future?
It is very unlikely. Both CM and SM appear to be complex inherited disorders caused by a number of different genes but also influenced by environmental (non-genetic) factors. DNA tests can be developed for conditions controlled by only one gene to definitively determine whether a dog is clear, a carrier or affected, but not for conditions controlled by more than one gene.
What statistics are known about the BVA/KC CM/SM?
Statistics on the number of dogs scored by the scheme and their results can be accessed in the Kennel Club’s Dog Health Group Annual Report.