WATCH: Adorable German Shepherd's rare condition means he will remain perpetually puppy-sized

Don't let his size fool you.

At 2 years old, Ranger is a full-grown German shepherd, but a rare genetic condition means the purebred pup will never grow any larger, Fox News reported.

Ranger's guardian, Shelby Mayo of Phoenix, told British news agency SWNS he was diagnosed with pituitary dwarfism – a rare genetic mutation to which the breed is susceptible – after he contracted a parasite called Giardia.

According to Fox News, the rare condition has also been known to affect other breeds such as the Saarloos wolfdog and the Karelian bear dog. Meanwhile, People magazine – citing the work of Claudia E. Reusch in "Canine and Feline Endocrinology" – reported a recessive gene inheritance is thought to play a role.

Click " target="_blank">here to watch Ranger in action.

In addition to his small stature, Ranger has also contended with myriad health issues associated with the hypothyroidism that accompanies his dwarfism – including flaky skin and excessive shedding – but he maintains the heart and energy of his full-sized counterparts, SWNS reported.

And while dogs with pituitary dwarfism typically have shortened lifespans, Mayo told the British news agency Ranger is as "healthy and happy as can be as of now and loves jumping around and playing with his ball and squeaky toys with his two sisters Hazel and Jessie."

Cox Media Group