There is defect in production of melanin in all except-
In melasma is a accuired hyperpigmentary disorder affecting predominantly over face. etiology is ultra violet rays. It is also triggered by pregnancy and oral contraceptive pills. All the other given conditions are associated with defects in melanin pproduction IADVL textbook of dermatology, pigmentary disorders,page745
Albinism
Vitiligo
Piebaldism
Melasma
Skin lesions and disorders of pigmentation