Mucopolysaccharidosis (MPS) in Dogs

Mucopolysaccharidosis (MPS) is a group of rare inherited metabolic disorders where the body lacks specific enzymes needed to break down complex sugars called glycosaminoglycans (GAGs). When those sugars can’t be broken down, they build up inside cells throughout the body, gradually affecting bones, joints, organs, the eyes, and in some types, the nervous system.

It’s a serious diagnosis, and while there’s no cure, understanding what’s happening and what support looks like can help you make the best decisions for your dog.

What is mucopolysaccharidosis in dogs?

Mucopolysaccharidosis (MPS) is a group of rare inherited metabolic disorders. It happens when the enzymes your dog’s body needs to break down glycosaminoglycans (GAGs) are missing or don’t function properly. GAGs are complex sugar chains that play an important role in building and maintaining connective tissue throughout the body. Think of them as structural scaffolding. When the enzymes that should clear them away aren’t working, GAGs accumulate inside cells, causing progressive damage to bones, joints, organs, the eyes, and in some types, the nervous system.

MPS is rare in dogs overall, but specific types occur more frequently in certain breeds due to inherited gene mutations.

Types of MPS in dogs

Different types of MPS are defined by which specific enzyme is missing. Each type affects different breeds and presents somewhat differently. Here’s what’s currently documented:

Type	Enzyme deficiency	Breeds most commonly affected	Key features
MPS I	Alpha-L-iduronidase	Plott Hounds	Skeletal abnormalities, corneal clouding, facial deformities
MPS II	Iduronate-2-sulfatase	Reported in dogs but extremely rare and poorly characterized; breed documentation is limited	Symptoms similar to MPS I
MPS IIIA	Heparan sulfamidase	New Zealand Huntaways; also reported in some Dachshunds	Primarily neurological, with progressive and often rapid cognitive and motor decline
MPS VI	Arylsulfatase B	Miniature Pinschers	Joint disease, skeletal deformities, corneal clouding, dwarfism
MPS VII	Beta-glucuronidase	Reported in mixed-breed dogs and some German Shepherds	Severe multisystem involvement

Symptoms of MPS in dogs

Symptoms often appear in puppyhood and vary depending on the type of MPS. Some signs are common across most types:

• Facial abnormalities, such as a broad, flat face or wide-set eyes
• Skeletal deformities, including shortened limbs and misshapen bones
• Joint swelling, stiffness, and difficulty moving
• Corneal clouding (A visible, milky film over the eyes that affects vision)
• Neurological decline, which can include seizures, loss of coordination, or behavioral changes
• Enlarged liver or spleen

The neurological forms, particularly MPS IIIA, tend to progress more rapidly than the skeletal-predominant types.

Diagnosis of MPS in dogs

If MPS is suspected, your vet will work through several tests to confirm it and identify the specific type:

• Urine GAG test: Measures elevated GAG levels in the urine, often the first screening step
• Enzyme activity assays: Blood tests that measure specific enzyme activity to identify which enzyme is deficient and therefore which type of MPS is present
• DNA testing: Available for some types, particularly in breeds known to be at risk
• Imaging (X-rays, MRI, ultrasound): To assess skeletal changes and organ involvement
• Biopsy: Occasionally used to examine tissue samples for GAG accumulation

Getting a specific diagnosis matters, because the type of MPS affects both prognosis and how care is prioritized.

Treatment and care for MPS in dogs

There’s no cure for canine MPS, and that’s genuinely hard to sit with. Treatment focuses on keeping your dog comfortable, managing symptoms, and slowing where possible the progression of complications.

• Pain management: Anti-inflammatory medications to address joint pain and stiffness
• Physical rehabilitation: Gentle movement exercises to maintain mobility for as long as possible
• Nutritional support: Dietary adjustments to support overall health and organ function
• Managing complications: Addressing secondary infections, vision problems, and other issues as they arise
• Experimental therapies: Enzyme replacement therapy (ERT) exists for several human MPS types but is not currently available for dogs. Bone marrow transplantation has been studied in animal models and may slow neurological progression when performed very early, but it is not widely available, carries significant risks, and remains experimental in dogs.

Your vet will help build a care plan based on your dog’s specific type and how symptoms are progressing.

Prognosis and quality of life

MPS is a progressive condition, and for many affected dogs, the prognosis is guarded. Lifespans can be significantly shortened, often measured in months to a few years depending on the type. Neurological forms like MPS IIIA tend to decline more rapidly, while types primarily affecting the skeleton may allow for a longer period of managed comfort.

This is hard news, and it’s okay to take time with it. The goal of care isn’t to reverse what’s happening, but to keep your dog comfortable, supported, and as mobile and pain-free as possible for as long as you can. Your vet can help you understand what the trajectory looks like for your dog’s specific type, and what quality-of-life markers to watch for as things progress.

Is MPS in dogs covered by pet insurance?

Yes, mucopolysaccharidosis is covered under Lemonade Pet’s base accident and illness policy, as long as it isn’t pre-existing. That includes eligible costs like diagnostic testing, pain management, and the ongoing supportive care that’s typically part of managing the condition long-term.

MPS is a serious diagnosis, and the cost of care is a real consideration alongside everything else you’re navigating. Having coverage in place before any symptoms appear means that when you’re focused on keeping your dog comfortable and supported, the financial side of things is already handled.

Once signs appear, the condition is typically considered pre-existing and won’t be eligible for coverage. If your dog is healthy now, especially if they’re a breed at higher risk, getting a policy in place is one of the most important steps you can take.

Before we go

A diagnosis of mucopolysaccharidosis is a lot to absorb, especially for a condition this rare. There’s no roadmap that fits every dog, and that uncertainty is hard. What helps most is staying close to your vet, understanding what your dog’s specific type means for their day-to-day life, and focusing on keeping them comfortable and supported as things evolve.

If you don’t have a pet insurance policy in place yet, it’s worth taking a few minutes to explore your options. Getting a quote is straightforward, and having coverage in place before anything develops puts you in a much stronger position when it matters most.

Frequently Asked Questions

A few quick words, because we <3 our lawyers: This post is general in nature, and any statement in it doesn’t alter the terms, conditions, exclusions, or limitations of the policies issued, which differ according to your state of residence. You’re encouraged to discuss your specific circumstances with your own professional advisors. The purpose of this post is merely to provide you with info and insights you can use to make such discussions more productive! Naturally, all comments by, or references to, third parties represent their own views, and Lemonade assumes no responsibility for them. Coverage may not be available in all states. Please note that statements about coverages, policy management, claims processes, Giveback, and customer support apply to policies underwritten by Lemonade Insurance Company or Metromile Insurance Company, a Lemonade company, sold by Lemonade Insurance Agency, LLC.  The statements do not apply to policies underwritten by other carriers.