The first cat they have seen that is not male or female is a homeless kitten.
Hope, a 15-week-old tabby and white cat, was thought to be female when it was admitted to the Cats Protection rescue centre, but vets found no sex organs.
Cats Protection's senior field veterinary officer,Fiona Brockbank, said it appeared to be a case of agenesis, the failure of an organ to develop.
Cats with male and female sex organs are rare, according to vets. Hope had no sex organs outside or inside.
Brockbank believes that there is an outside chance of some ectopic ovarian tissue hiding away inside.
We didn't have any previous cases on which to base our knowledge of how this will affect Hope in the future, so we spent time monitoring this cat to ensure they can urinate and defecate appropriately before they were considered ready for re-homing.
Hope, who is described as a playful kitten, has endeared itself to staff and volunteers at Cats Protection's Warrington adoption center, where it was first admitted and underwent investigations.
"Discovering Hope's special status has been an exciting time as no one has seen this before or is likely to again."
Hope has been a pleasure to care for and it is great that they are going to be adopted. They will bring a lot of fun and friendship. We would love to hear about our star.