Cornish Rex — questions to ask before paying a deposit
A responsible breeder will have these readily available. Deflection is a red flag.
Hypokalaemia
Cornish Rex is named on the WNK4 hypokalaemia test's VGL breed list alongside the Burmese group. The mutation causes episodic muscle weakness from low blood potassium.
Ask to see: WNK4 DNA test, UC Davis VGL, explicitly validated for Cornish Rex. Usually managed with oral potassium supplementation once identified.
Hypokalemia (WNK4) DNA test -- breed list includes Cornish Rex, UC Davis Veterinary Genetics Laboratory (https://vgl.ucdavis.edu/test/burmese-hypokalemia)
Neonatal isoerythrolysis risk (blood type B)
Cornish Rex is named by UC Davis VGL as one of the breeds with a high frequency of the blood type B allele. A type B queen mated to a type A or AB tom risks kittens developing neonatal isoerythrolysis after nursing colostrum containing anti-A antibodies.
Ask to see: AB blood typing test (UC Davis VGL and other labs). Both breeding partners should be blood-typed before pairing.
Feline AB Blood Type test -- notes Cornish Rex among breeds with high blood type B frequency, UC Davis Veterinary Genetics Laboratory (https://vgl.ucdavis.edu/species/cat)