Epidemiology, Signs and Symptoms of Inherited Retinal Dystrophies Flashcards
(34 cards)
What is a genotype?
your genetic classification
e.g. you have a mutated gene that codes for a protein that leads to a disease
What is a phenotype?
Physical appearance
e.g. you actually show the disease
- this depends upon the mode of inheritance and penetrance
What is x-linked?
The gene is coded on the X chromosome
- females have 2, males have 1
What is autosomal?
The gene is coded on one of the 22 non-sex chromosomes
What is dominant?
In order to show the phenotype you only require 1 mutated gene
What is recessive?
In order to show the phenotype you require 2 copies of the mutated gene
What is penetrance?
Even if you have the genotype you may not get a severe form of the disease
What is Retinitis Pigmentosa?
A collection of inherited disorders that share a common set of signs and pathology
What happens with Retinitis Pigmentosa?
- Px present with nyctalopia (night blindness ) due to progressive cell loss and retinal dystrophy
- Starts peripherally and progresses towards the posterior pole
- Rods are affected
What are classic signs of Retinitis Pigmentosa?
- Bone-spicule pigment
- initial halo around disc : later peripapillary atrophy
- arteriolar narrowing
- waxy, pale optic nerve head
- early onset cataract
Why does Retinitis progress?
due to mutations that may result in ineffective RPE phagocytosis of rod outer segments
- debris accumulates, causing rod dysfunction and death
How does the functional loss show?
- The electroretinogram shows loss of a-wave : definitive diagnosis
- progressive visual field loss with ring scotoma due to there being no rods in the fovea and far periphery is not affected
What is Usher’s Syndrome?
syndrome that includes both vision and hearing loss
- affects the autosomal recessive gene
- progression from RP from childhood
What is the diagnosis of RP?
- nyctalopia primary presenting complaint
- delayed recovery to photostress test
- ERG is the definitive diagnosis with a reduced a-wave seen
- peripheral vision loss may be noticed
What is Cone Rod Dystrophy?
Large group of genetically diverse conditions that present with macular pigmentary changes that are not age related
- affect cones
What are symptoms of Cone Rod Dystrophy?
- VA loss
- Colour vision defect
- photophobia
- later rods become involved as RPE fails and nyctalopia is observed
What are homeobox genes?
CRX photoreceptors survival gene
- leads to autosomal dominant cone rod dystrophy
What is retinoid metabolism?
ABCA4; responsible for 30-60% of autosomal recessive cases
- mutations also seen in Stargardt disease
What are the diagnosis tests for Cone Rod Dystrophy?
- visual field which shows central loss
- Cone ERG amplitude significantly reduced
What are DDX for Cone Rod Dystrophy?
- Leber’s : congenital
- Stargardt’s presents with white/yellow flecks over fundus prior to any macular scarring
What is Congenital Stationary Night Blindness?
Present at birth, not progressive and the primary symptom is nyctalopia
What is type 1 CSNB?
- Abnormal dim scotopic ERG
- bright flash remains normal
What is type 2 CSNB?
- Very abnormal dim scotopic
- Abnormal light flash : a wave is present but no b-wave or oscillatory potentials
What is Oguchi Disease?
This is a variant of CSNB
the retina has a strange golden appearance that disappears with dark adaptation
- has a autosomal recessive pattern
