New DNA test launched for previously undiagnosed condition in Giant Schnauzers

Animal Health Trust identifies blinding condition in Giant Schnauzers, finds genetic mutation which causes it and promptly launches DNA test

We have identified an inherited retinal disease, progressive retinal atrophy (PRA), which leads to blindness in Giant Schnauzers.

A dog suffering with PRA may begin to lose its vision in lowlight at night, have problems seeing obstacles or finding its way around in familiar surroundings. Over a period of months, or years, their visual impairment increases and unfortunately all dogs with PRA will eventually go blind.

The condition, for which there is no treatment, is well documented in more than 100 breeds of dogs but was previously unrecognised within Giant Schnauzers.

But now, thanks to the work of vets and scientists at the Animal Health Trust (AHT), a DNA test has been developed to eradicate the disease within the breed before it is able to take hold.

The Kennel Club Genetics Centre at the AHT received DNA samples from a litter of four year old Giant Schnauzers. Two of the seven littermates had previously been diagnosed with PRA.

Follow up examinations of one additional dog in the litter and both parents at the AHT’s Small Animal Referral Centre revealed that in fact three of the seven littermates had PRA and both parents were clinically clear of the disease. This confirmed the presence of an autosomal recessive PRA, where an affected dog has to carry two copies of the PRA-causing variant in order to develop the disease.

A genetic study was launched to identify the causal mutation, and results of this research show that mutation is rare within the breed, with approximately one in 35 dogs carrying the genetic mutation.

As this condition in the Giant Schnauzer is quite rare we’re not expecting to find many affected dogs through DNA testing, but it is crucial to identify any carriers in order to prevent more puppies being born with this blinding condition, and to stop it becoming more widespread in future

Rebekkah Hitti, Research Assistant and PhD Student at the AHT

Rebekkah added “We’ve had a good level of interest in this research so far from Schnauzer breeders and we’re confident that this breeding community is keen to get this mutation under control, and in time, eradicate it safely from their breed altogether.”

How the mutation was found

In order to find the mutation responsible, the AHT used whole genome sequencing technology to study all 2.4 billion letters of DNA from just two of the affected Giant Schnauzer littermates, and both unaffected parents.

Traditionally, a genetic investigation into a disease of this nature would require DNA samples from at least twelve affected dogs and the same number of healthy control dogs from the same breed. Now, advanced genome sequencing technology and the use of state-of-the-art computer analysis allows every letter of DNA from a single affected dog to be interrogated and compared to a bank of genome sequences of healthy dogs from different breeds, in order to find the change in DNA responsible for a specific inherited disease. This approach allowed the genetics of PRA in the Giant Schnauzer to be investigated straight away, without collecting additional DNA samples.

The causal mutation was quickly identified as a single letter change in the 2.4 billion letter DNA code. Once this mutation had been pinpointed, it was confirmed by comparison against the genotypes of more than 5,000 different dogs across UK and European genome banks, including those stored in the AHT’s Canine Genome Bank, which is the largest in the UK. Only the Giant Schnauzers with PRA had two copies of the genetic mutation needed to cause the disease.

Rebekkah added: “Our study looked at DNA from a mixture of pepper and salt, and black Giant Schnauzers, and we identified carriers of both colour types. We also found dogs with carrier status in additional breeds of German origin, including Spitz and Dachshund varieties although the significance of this finding is unknown at present.”

We would like to thank the Schnauzer Breed Clubs for their help and support and all the owners who participated in this study.

Rebekkah Hitti, Research Assistant and PhD Student at the AHT

The DNA test for PRA in Giant Schnauzer, costing £48, is available from the AHT DNA Testing Service by clicking here