Albinism

Question 1

oculocutaneous albinism features

Answer 1

• 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

Question 2

OCA types

Answer 2

• 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.

Question 3

OCA prevalence

Answer 3

1 in 20K

Question 4

race predilection of OCA

Answer 4

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.

Question 5

what is th emost severe form of OCA?

Answer 5

OCA1A

Question 6

name all the OCA variants?

Answer 6

• 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).

Question 7

why does albinism occur?

Answer 7

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

Question 8

what is the result of a mutation on TYR gene?

Answer 8

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.

Question 9

name the biochemical sequence of melanin synthesis

Answer 9

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

Question 10

name the OCA type and the respective mutation

Answer 10

• 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).

Question 11

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

Answer 11

1. OCA
2. OA

OCA is by far more common

overall prevalence is 1 in 20K to 40K worlwide

Question 12

causes of TIDs?

Answer 12

• OCA and OA
• pigment dyspersion syndrome
• pseudoexfoliaiton syndrome
• iris atrophy
• axenfeld rieger
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Question 13

what type of nystagmus do you see in albinism?

Answer 13

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.

Question 14

tell me about the abnormal fiber decussation…

Answer 14

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

Question 15

how is albinism inherited?

Answer 15

its an autosomal RECESSIVE disorder

so we need TWO copies

Question 16

how many types of OCA and OA are there?

Answer 16

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

For OA there ate 2 types.

Question 17

whatis albinoidism?

Answer 17

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

Question 18

tell me about OCA type 1

Answer 18

• 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.

Question 19

tell me about OCA type 2

Answer 19

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