As everyone is saying, check with a vet. It is possible it is agenetic defect...at least years ago I adopted a parakeet that was unsaleable because she had inherited a trait that ment she would never develop adult feathers on two patches of her wings. It caused her no pain and she was a sweet and loving companion to my other 'keet and me. It ment she was never able to fly very well which frustrated the other 'keet, but again, she lived a lomg a happy life with her patches of down.