While the exact mode of inheritance is unknown, it is probably polygenetic. (mascaonline.com)
The congenital form of medial luxation (kneecap dislocated to the inside of the knee) is most common in toy breeds, not excluding Havanese, and is considered inherited although the exact mode of inheritance is not known. (havanesefanciers.com)
The exact mode of inheritance of LPD has been debated among researchers. (italiangreyhound.org)