Albinism is primarily characterized by a deficiency in which of the following?

Albinism is primarily characterized by a deficiency in melanin pigment. Melanin is the natural pigment responsible for the coloration of the skin, hair, and eyes in humans and many other organisms. In individuals with albinism, there is a genetic mutation that leads to a lack of melanin production, resulting in lighter skin, hair, and often light-colored eyes. This deficiency also significantly impacts visual acuity and the ability to tolerate sunlight due to less protection against UV radiation.

The other options focus on different biological aspects not directly related to albinism. For example, phenylalanine is an amino acid and while its levels are important in conditions like phenylketonuria, it does not relate to the pigmentation process affected in albinism. Nerve cell destruction pertains to various neurological disorders, and red blood cell count is a measure of hematological health, neither of which characterizes the condition of albinism. Thus, the primary hallmark of the condition is indeed related to the deficiency of melanin pigment.