Jack Russell Terrier — questions to ask before paying a deposit
A responsible breeder will have these readily available. Deflection is a red flag.
Primary lens luxation (PLL)can shorten life or cause chronic pain
The lens of the eye detaches from its normal supporting fibres, usually between 3 and 8 years old; it is painful, can cause secondary glaucoma, and is usually treated as a same-day surgical emergency. The causative ADAMTS17 mutation was first identified in this breed (together with the Lancashire Heeler and Miniature Bull Terrier).
Ask to see: DNA test result for the ADAMTS17 primary lens luxation mutation on both parents — part of the UK Kennel Club's official testing scheme, and also offered by UC Davis VGL, Laboklin and other laboratories.
UC Davis Veterinary Genetics Laboratory — Primary Lens Luxation (https://vgl.ucdavis.edu/test/primary-lens-luxation) · PubMed — 'ADAMTS17 mutation associated with primary lens luxation is widespread among breeds' (https://pubmed.ncbi.nlm.nih.gov/22050825/)
Spinocerebellar ataxia with myokymia and/or seizurescan shorten life or cause chronic pain
A juvenile-onset neurological disease (KCNJ10 gene) causing progressive incoordination from as young as 2 months old, often with muscle twitching (myokymia) and seizure-like episodes; affected dogs are usually euthanised before 3 to 4 years old because of declining quality of life. Documented directly in Jack Russell Terriers, not inferred from a related breed.
Ask to see: DNA test result for the KCNJ10 mutation on both parents, sold as 'spinocerebellar ataxia, terrier type' by Paw Print Genetics/Orivet, Laboklin, Canine Genetic Testing (CAGT) and others.
Journal of Veterinary Internal Medicine — Gilliam et al. 2014, homozygous KCNJ10 mutation in Jack Russell Terriers (https://onlinelibrary.wiley.com/doi/pdf/10.1111/jvim.12355) · BMC Veterinary Research — Gast, Metzger, Tipold & Distl 2016 (https://pmc.ncbi.nlm.nih.gov/articles/PMC5057501/)
Congenital sensorineural deafnesscan shorten life or cause chronic pain
Deafness present from birth in one or both ears, associated with the breed's predominantly white coat pattern; it does not progress or improve and has no treatment. The parent club treats it as a genetic issue to be bred away from, not an individual misfortune.
Ask to see: Not a DNA test — a BAER (brainstem auditory evoked response) hearing-test result on the individual dog, performed after 5 weeks of age, per the Jack Russell Terrier Club of America's protocol. Ask whether the breeding stock and the litter itself were BAER tested.
Jack Russell Terrier Club of America — BAER Testing FAQ (https://www.therealjackrussell.com/advice/faqhearing.php)