If you are sure that your other kittens have no symptoms, and that the affected kitten has no symptoms other than hair loss, the only condition I can think of would be Congenital Hypotrichosis. This is an inherited condition, although the mode of inheritance has not yet been established. There seems to be a higher incidence of the congenital form of this disease in male kittens and puppies, suggesting that sex-linked inheritance is involved. Certainly, just because both parents are unaffected does not mean this inherited condition is not the cause of the symptoms, since inheritable conditions can be "carried" without symptoms being expressed.

Congenital Hypotrichosis is known to occur in several cat breeds, including the Devon Rex and Siamese. In Birman cats, affected cats have no thymus, and in the Burmese breed affected cats have no claws, tongue papillae or whiskers. If your kitten is not a purebred Birman or Burmese cat, it is likely that there are no other symptoms, however you should check the tongue, teeth and claws for abnormalities. In later life, Congenital Hypotrichosis can cause dermatological (skin) conditions even if there are currently no other symptoms. Additionally, affected cats may be more susceptible to sunburn and skin allergies.

If your kitten develops any additional symptoms, or any other kitten in the litter develops this symptom or any other symptom you should have them thoroughly examined by your veterinarian.