Albinism

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Phenotypes in a domestic cat pedigree that segregated for albinism: (a) albino, (b) a Colourpoint (chocolate lynx-point non-albino) sibling ; and c) a litter of kittens that includes an albino (third from the left).[1]
Complete achromia in a young female DSH cat with tyrosinase-positive oculocutaneous albinism
White DSH with subalbinotic eye. Note that the iris lacks pigment and is almost translucent. The pink fundus reflex indicates a similar lack of pigment and also absence of tapetum in the fundus

Albinism constitutes a rare disease of the iris, where there is an absence of normal pigmentation which can frequently be related to coat colour[2].

The only types of oculocutaneous albinism (OCA type 1) that have been described in the cat are those associated with mutations on the albino locus of the gene encoding for tyrosinase, which in affected cats leads to inactivity of this enzyme. Recently, the causative mutations for the siamese and burmese temperature-sensitive alleles have been identified in tyrosinase[3].

OCA type 1 is characterised clinically by complete loss of pigmentation not only of the coat and skin (white coat) but also in retinal and choroidal epithelium in the eye, with associated abnormal optic visual fibres cross over and severe ocular abnormalities (e.g. reduced visual acuity, loss of binocular vision)[4].

White is a common coat color of cats and partial or complete congenital deafness is not uncommon in white cats, especially when one or both irides are blue[5]. Blue-eyed versus pink-eyed albino cats have not been clearly distinguished in the published reports[6]. Thus, it is unclear whether there is more than one non temperature-sensitive albinism allele in cats. Albino cats in a study by Imes et al (2006) had blue eyes. As with most blue-eyed cats, reduced pigment in the tapetum produces a ‘reddish’ (as opposed to a ‘greenish’) tapetal reflection or ‘eye-shine’. The c allele has been reserved for red-eyed (complete) albinism, but the difference in the tapetal reflex suggests that the single report of a red-eyed albino cat may be in error.

Chediak-Higashi syndrome is a rare type of partial oculocutaneous albinism, which is inherited as an autosomal recessive disease and abnormalities include cataracts and decreased pigmentation of the iris and fundus.

References

  1. DL Imes, LA Geary, RA Grahn, & LA Lyons (2006) Albinism in the domestic cat (Felis catus) is associated with a tyrosinase (TYR) mutation. Anim Genet 37(2):175–178
  2. Barnett, KC & Crispin, SM (2002) Feline ophthalmology: An atlas and text. Saunders, USA
  3. Lyons LA, Imes DL, Rah HC, Grahn RA (2005) Tyrosinase mutations associated with Siamese and Burmese patterns in the domestic cat (Felis catus). Anim Genet 36(2):119-26
  4. Guaguere, E & Prelaud, P (2000) A practical guide to feline dermatology. Merial, France
  5. Bergsma, DR & Brown, KS (1971) White fur, blue eyes and deafness in the domestic cat. Journal of Hereditary 62:171-185
  6. Leventhal AG, Vitek DJ, Creel DJ. (1985) Abnormal visual pathways in normally pigmented cats that are heterozygous for albinism. Science 229:1395–1397