Albinism and its Ocular Manifestations Flashcards
What is Albinism?
The result of reduced or absent melanin biosynthesis
What are the two classification groups of Albinism?
- Oculocutaneous albinism (OCA)
- Ocular albinism (OA)
What is melanin?
melanin is produced and contained within melanosomes which is an organelle within melanocytes and retinal pigment epithelium
What is the classification of oculocutaneous?
- hypopigmentation of the skin, hair and eyes
due to a reduction in, or a complete lack of production of melanin - high degree of heterogeneity in pigmentation presentation
What is the classification of ocular albinism?
hypopigmentation primarily affecting the retinal pigment epithelial cells
- hair and skin remain pigmented
What are the 7 genetics of oculocutaneous?
- OCA1 : TYR
- OCA2 : OCA2
- OCA3 : TYPRP1
- OCA4 : SLC45A2
- OCA5 : chromosome location known but gene not defined
- OCA6 : SLC24A5
- OCA7 : C10orf11
What is an AR mutation?
Androgen receptor
What is the OCA1 gene?
two subtypes OCA1A (^severe) and OCA1B
TYR encodes tyrosinase the most important enzyme in melanin biosynthesis
What is the OCA2 gene?
OCA2 encodes P-protein, a melansome membrane protein
What is the OCA3 gene?
Also known as known as Rufous oculocutaneous albinism
TYRP1 encodes tyrosinase-related protein 1
What is the OCA4 gene?
- it encodes a melanosome membrane protein
What is the OCA5 gene?
A non-syndromic AR cause of OCA
What is the OCA6 gene?
- it encodes for the NCKX5 protein
What is the OCA7 gene?
encodes a 198 amino acid protein with 3 leucine-rich repeats and its associated with melanocyte differentiation
What are the signs and symptoms?
- Visual disturbances
- High degree of heterogeneity in pigmentation presentation depending upon the gene
What is the colouration of OCA1A?
- hair, eyelashes and eyebrows are white
- skin is white and does not tan
- pigment does not develop through life
What is the colouration of OCA1B?
- typically born with white hair, eyelashes, eyebrows and pale skin
- develop some melanin pigment in hair and lashes over time
- skin may tan - freckles
What is the colouration of OCA2?
- degree of skin pigmentation varies, pale at birth
- nearly always have pigmented hair at birth often blonde or red
What is the colouration of OCA3?
Red hair and reddish-brown skin
What is the colouration of OCA5?
golden-coloured hair and white skin
What is the coloration of OCA6?
- Hair colour varies from white to blonde or dark brown
- hair darkens with age
What is the colouration of OCA7?
pigmentation varies
- present with lighter pigmentation than unaffected relatives
What is the iris colour for OCA1A?
light blue to almost pink, fully translucent
What is the iris colour of OCA1B?
blue irides that may change to green/brown with age
