Polycystic kidney disease (PKD) is one of the most common hereditary diseases in Canada, affecting roughly one Canadian in every 500. The disease is characterized by the growth of abnormal cysts in the kidneys, causing them to enlarge and eventually crowd out the normal kidney cells vital to survival.

The disease has several variants, including multiple versions of what’s known as autosomal dominant PKD, as well as the much rarer autosomal recessive PKD, which is usually aggressive very early in life. In all cases, the disease is genetic, with no practical way to prevent it. And, until recently, there were a very limited number of therapies effective at targeting it.

"As with any kind of therapy, the key thing is to have a very frank and well-informed conversation between the doctor and the patient."

Why existing drugs don’t help

Because PKD functions differently from other kidney diseases, the drugs that are effective in treating those other diseases of the kidney are of little help against PKD. “Normally in most progressive kidney diseases we look at kidney function, which is measured by Glomerular Filtration Rate (GFR),” explains Dr. Sanjay Pandeya, Nephrologist and Medical Director, Independent Dialysis and Kidney Function Clinic at Halton Healthcare Services.

“Most drug approval processes, in Canada and worldwide, when considering if a drug is indicated for kidney disease, investigate the effect the drug has on the GFR over time. But PKD is a bit of an outlier because it is largely a structural kidney disease with the GFR being affected only in the late stages.”

Patients with PKD will often show healthy kidney function as the disease develops. Cysts will grow in the kidneys, increasing kidney volume, which often means that the first diagnosis comes not from GFR blood testing but from an ultrasound as a result of abdominal pain or blood in the urine. Even so, as the cysts grow and the kidney volume increases, the healthy parts of the kidneys work in overdrive and are capable of maintaining normal kidney function — until they aren’t.

So patients with PKD experience a steady rise in total kidney volume without the corresponding loss of kidney function, until a certain threshold is reached and sudden kidney failure results. Therefore finding a therapeutic drug to combat this disease required looking at kidney drug efficacy in an entirely new way.

Canada leads the way on adopting new treatments

A new drug has recently been developed in Japan which has little effect on GFR, but shows a marked effect on total kidney volume. Understanding this new metric was vital to introducing a new therapy for PKD. “The drug prevents the increase in total kidney volume over time,” says Dr. Pandeya.

“What that means is that it is preventing the development of the cysts that lead to eventual replacement of normal functioning kidney tissue which in time leads to kidney failure. And Health Canada, after reviewing the facts, agreed with total kidney volume as a valid assessment of the drug’s efficacy. As a result, Canada became the second country in the world to approve the drug, after Japan, the originating country.”

For Canadians living with PKD, this means that the options for treating their disease have grown dramatically. “It’s not for everyone with the disease,” Dr. Pandeya cautions. “It’s important to treat patients as individuals and look at whether they, specifically, are likely to benefit from the drug. As with any kind of therapy, the key thing is to have a very frank and well-informed conversation between the doctor and the patient.”

For all patients, however, each new therapy developed brings a new ray of hope.