Albinism is a genetic condition characterized by compromised melanin production. Melanin is a vital pigment which determines the color of the skin, eyes and hair.
Very light skin color, red to brown hair, and light blue or brown colored eyes are usually observed in individuals with albinism. Due to the low levels of melanin, the skin of such people has a very high sensitivity to sun exposure, conferring a high risk of developing skin cancer.
Melanin is also important in the functioning of the optic apparatus. Therefore, individuals with albinism are also more prone to develop visual impairment.
Albinism is essentially a pediatric disease. The diagnosis is simple, being based on the baby’s appearance. However, in a few cases, the lack of pigmentation becomes apparent later. Poor visual acuity may be the first sign in such infants, followed by the appearance of other symptoms more gradually around the age of 3 to 4 months of life.
Two major types of albinism have been reported, which include ocular albinism (OA) and oculo-cutaneous albinism (OCA). While OA is quite rare and affects mainly the eyes, OCA also affects skin and hair. Several other subtypes have also been categorized based on different inheritance patterns and genetic triggers.
OCA is inherited in the autosomal recessive form. Parents of a patient with OCA are asymptomatic carriers, each possessing one defective copy of the affected gene (such as the GPR143 gene). There exists a 50% probability in each pregnancy that any child born to such parents will be a dormant carrier of the disease (just like the parents), a 25% probability that the offspring will be born without any defect in the said gene, and a 25% probability that the child will be born with OCA symptoms.
Unlike OCA, OA is usually passed on via an X-linked inheritance pattern, which means that it affects the genders differently. Because males have only one X chromosome, the mutation of a gene on the single X chromosome in a male leads to the manifestation of definitive signs and symptoms of OA. On the other hand, a female with a mutated copy of gene on one of the two X chromosomes may still manage to have normal vision because of the normally functioning copy of the gene on the other X chromosome.
Therefore, a male may either have an active OA disease or have no OA gene defect at all, but he can never be a carrier of an X-linked mutation. In contrast, a female may typically be a carrier of an X-linked mutation, but rarely develop the symptoms. When a mother is a carrier of such a mutation, there exists a 50% probability with each pregnancy that her daughters might be born as carriers (just like the mother), and a 50% probability that her sons could be born with the symptoms of OA. When a father has X-linked albinism, there is a 100% probability that his daughters will be born as carriers his sons will be born without the said gene mutation, because the single X chromosome in a male offspring is from the (normal) mother.
Several other mutation patterns have been identified which may result in albinism and related symptoms. Hermansky-Pudlak syndrome (HPS) is one such condition which is due to a mutation in any of nine different genes on different chromosomes. HPS is a relatively rare disorder with symptoms similar to OCA, but with bruising and bleeding symptoms in addition. It is also inherited in an autosomal recessive pattern like OCA.
Chediak-Higashi syndrome is another rare type of albinism which occurs due to mutation in the LYST gene. In addition to the OCA-like symptoms, the patients with this disorder also have defects in the lymphocytes which make them vulnerable to various infections.