Chondrodysplasia (short-leg dwarfism)
A dominant mutation shortens the long bones of all four limbs; it is the Munchkin's defining trait, present in every cat that has it, and lethal before birth in kittens that inherit two copies. Short, abnormally loaded limbs may predispose affected cats to painful osteoarthritis and reduced jumping ability, though the welfare literature itself says this has not been formally measured. This is genuinely contested rather than settled: UFAW (an academic animal-welfare body) states that many pedigree associations refuse to recognise the breed for this reason and recommends affected cats not be bred from, while TICA and breed advocates maintain that most Munchkins move and behave normally. Both positions are reported here rather than one being picked.
What to ask for
No DNA test is offered or needed — the trait is visible at birth. Ask about the cat's activity level and any signs of joint stiffness, and whether older breeding cats have had their joints checked or X-rayed.