Albinism is not a disease as most believe it to be; it is in simple words, a disorder caused due to the mutation in the genetic setup of the individual's body. Albinism can best be defined as a congenital disorder, which affects the pigment production in the skin, hair and eyes due to the absence of enzymes that help produce melanin. The main cause of albinism is a mutation occurring in one of the many genes, which provide the chemically coded instructions for making several proteins involved in the production of melanin.
Causes for Different Types of AlbinismBasically, the root cause of albinism is mutations of various genes present in chromosomes in an individual's body. The main types of albinism are:
»Oculocutaneous type: It affects the pigment production in the eyes, skin and hair.
»Ocular type: It affects only the melanin production of the eyes.
Given below is a table which will give you an in-depth analysis of the causes of the different types of albinism.
|Oculocutaneous Albinism Type 1 (OCA1)|
|Cause||Mutation inTyrosinase Gene (TYR gene)||Found inChromosome 11|
|Description||Patients showing symptoms of OCA1 have mutations in the TYR gene found on the chromosome 11. TYR is located in melanocytes and is responsible for the first step of melanin production. It helps convert a protein building block called tyrosine to another compound called dopaquinone. TYR mutations eliminate the activity of tyrosinase thus, preventing melanocytes from producing any melanin all through the lifespan of the affected individual. Depending on the variation in the mutation, this type is subclassified into two types, namely OCA1a and OCA1b.|
|Subclassification||OCA1a: Melanin production in this type is severely hampered.||OCA1b: Production of some melanin is possible. It is further subclassified into two types: OCA1b TS(temperature sensitive) in which, the tyrosinase functions below a certain temperature and OCA1b YM(yellow mutant type), which affects the Amish population.|
|Oculocutaneous Albinism Type 2 (OCA2)|
|Cause||Mutation of the P-Protein||Found inChromosome 15|
|Description||Considered to be the most common type of albinism, it is caused due to the abnormal mutation of the P-protein (also called theOCA2 gene) found in the melanosomal membrane in chromosome 15. The P-protein is involved in the molecule transport of tyrosine from melanosomes.|
|Oculocutaneous Albinism Type 3 (OCA3)|
|Cause||Mutation of theTyrosinase-related Protein 1 (TYRP1)||Found inChromosome 9|
|Description||It is a rare form of gene mutation, which is observed mostly in Africans. It occurs due to the mutation of the tyrosinase-related protein 1 (TYRP1) found in chromosome 9. It is also known as Rufous Oculocutaneous Albinism(ROCA) or Xanthism.|
|Oculocutaneous Albinism Type 4 (OCA4)|
|Cause||Mutation in theMembrane-associated Transporter Protein(MATP)||Found inChromosome 5|
|Description||Similar to OCA2, the OCA4 is caused due to the mutation of the membrane-associated transporter protein gene (MATP) or theAbsent in Melanoma 1 (AIM1) gene. It is inherited in an autosomal recessive (presence of two copies of a gene mutation) manner. It is observed mostly in Europeans and East Asian descent.|
|X-linked Ocular Albinism (OA1) or (XLOA)|
|Cause||Mutations in the G-Protein Coupled Receptor 143(GPR143) gene||Found on the X chromosome|
|Description||Known to affect only males, this type of albinism is inherited when the disorder is located on the X chromosome. Just one altered gene is enough to cause this type of albinism. The cause for this is due to female obligate carriers (the individual remains unaffected but carries the gene mutation).|
|Cause||Mutation in any one of the 8 genes, namelyHermansky-Pudlak Syndrome Protein (HPSP), Subtype 1-8||Found in theChromosome 10|
|Description||Mutation in any one of the following genes will result in this type of albinism. They include: Hermansky-Pudlak Syndrome 1 Protein (HPS1), Adapter-Related Protein Complex 3 subunit Beta-1 (AP3B1 or HPS2), Hermansky-Pudlak Syndrome 3 Protein (HPS3), Hermansky-Pudlak Syndrome 4 Protein (HPS4), Hermansky-Pudlak Syndrome 5 Protein (HPS5), Hermansky-Pudlak Syndrome 6 Protein (HPS6), Dystrobrevin-binding Protein 1 (DTNBP1 or HSP7) and Biogenesis of Lysosome-related Organelles Complex 1 Subunit 3 (BLOC1S3 or HPS8). People with HPS lack dense bodies in their blood platelets, which are responsible for releasing clotting factors. It is a single-gene disorder inherited in an autosomal recessive manner. It is a form of albinism associated with a bleeding tendency (bleeding disorder) along with problems of lungs (lung fibrosis) and bowel diseases.|
|Cause||Mutation in theLysosomal Trafficking Regulator(LYST) gene||Found in theChromosome 1|
|Description||It is a rare autosomal recessive disorder, which arises due to the microtubule polymerization defect that leads to decrease in phagocytosis, which in turn, results in recurrent pyogenic infections and partial albinism.|
To conclude I must say, thank your stars if you were blessed with good genes, yet do not indulge in poking fun at someone who is less privileged. After all, skin color does not make a man any less different from you. Besides, you cannot judge people on the basis of their appearances, as albino people are as much human as you or I are!