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Flashcards in Albinism Deck (20):

oculocutaneous albinism features

- its an inherited disorders of melanin biosynthesis 

- light colored hair -light colored skin - light colored iris - blonde retina -hypoplasic fovea -nystagmus -strabismus - reduced vision, photophobia


OCA types

  • type 1:  white hair, very pale skin, and light-colored irises.
  • Type 2: less severe than type 1; the skin is usually a creamy white color and hair may be light yellow, blond, or light brown.
  • Type 3  usually affects dark-skinned people. Affected individuals have reddish-brown skin, ginger or red hair, and hazel or brown irises. Type 3 is often associated with milder vision abnormalities than the other forms of oculocutaneous albinism.
  • Type 4 has signs and symptoms similar to those seen with type 2.


OCA prevalence

1 in 20K


race predilection of OCA

Types 1 and 2 are the most common forms of this condition; types 3 and 4 are less common. Type 2 occurs more frequently in African Americans, some Native American groups, and people from sub-Saharan Africa. Type 3, specifically rufous oculocutaneous albinism, has been described primarily in people from southern Africa. Studies suggest that type 4 occurs more frequently in the Japanese and Korean populations than in people from other parts of the world.


what is th emost severe form of OCA?



name all the OCA variants?

  • OCA1A (the most severe form),
  • OCA1B, OCA1-minimal pigment (OCA1-MP),
  • OCA1-temperature sensitive (OCA1-TS),
  • OCA2, OCA3, OCA4, OCA5, OCA6 and OCA7 (see these terms).


why does albinism occur?

due to mutations in the genes that control the synthesis of melanin


what is the result of a mutation on TYR gene?

 OCA1A, OCA1B, OCA-MP and OCA-TS are caused by mutations in the TYR gene (11q14.3), leading to a total or partial loss of the catalytic activity of tyrosinase.


name the biochemical sequence of melanin synthesis

  1. tyrosine
  2. hydroxylase action to...
  3. DOPA
  4. Tyrosinase action to...
  5. Dopaquinone
  6. Melanine


name the OCA type and the respective mutation

  • OCA1 = TYR gene (11q14.3)
  • OCA2 = OCA2 gene (role in melanosomal proteins)
  • OCA3= TYRP1 gene causing early degradation of tyrosinase
  • OCA4= SLC45A2 gene encoding the membrane-associated transporter protein (MATP) that is responsible for melanosome function and protein transport
  • OCA 5 mutation chromosome 4q24, whose gene has not yet been discovered.
  • OCA6 is due to mutations in the SLC24A5 gene (15q21.1). Recently discovered
  • OCA7 is due to a mutation in C10orf11 gene (10q22.3).


albinism can be dividen in what 2 groups and which is more common?

  1. OCA
  2. OA

OCA is by far more common

overall prevalence is 1 in 20K to 40K worlwide


causes of TIDs?

  • OCA and OA
  • pigment dyspersion syndrome
  • pseudoexfoliaiton syndrome
  • iris atrophy
  • axenfeld rieger


what type of nystagmus do you see in albinism?

pendular nystagmus

infants may have large amplitude with low frequency pattern of eye movement starting at 2-3 months of age, later changing to a pendular form without distinct fast or slow phases. Eye muscle surgery may be considered to reduce nystagmus.


tell me about the abnormal fiber decussation...

  • normally 50% of fibers decussate
  • in albinism almost 90% decussate
  • can do VEP to detect this


how is albinism inherited?

its an autosomal RECESSIVE disorder

so we need TWO copies


how many types of OCA  and OA are there?

  • SEVEN types. 
  • 'its a genetic classification
  • all are autosomal recessive
  • all have nystagmus

For OA there ate 2 types.


whatis albinoidism?

  • autosoma dominant condition
  • hupopigmented skin
  • normal vision., normal eyes


tell me about OCA type 1

  • TYR gene mutation
  • 4 subtypes 
    • OCA1A - most severe form, high risk skin cancer, was know as tyrosinase negative
    • OCA1B - yellow variant” due to reduced, but not absent, tyrosinase activity that produce some pigment. Gainpigment through life. mild vision impairment
    • OCA 1MP. minimal pigment. increased iris pigment through life. Dopa positive
    • OCA 1TS tyrosinase activity is inversely proportional to temperature, leading to dark hair on the cooler extremities but white hairs near the body core such as the axilla, pubic area, and scalp. 


tell me about OCA type 2

  • the most common
  • highest frequency in Equatorial Africa
  • OCA2 gene
  • milder than type 1