Choroideremia
Patient Information
Characteristics
Background and History
Choroideremia was so named because it was thought to be due to an absence of the vascularized layer (choroid) in the eye. It was later found that all layers of the retina and of the choroid in the eye are degenerated but the name has persisted.
Clinical Correlations
Choroideremia is a disease found primarily in males which begins in early childhood with night vision difficulties resulting from progressive damage to the cells in the retina that detect light (rods and cones, or photoreceptors). These are highly concentrated in a ring around the central area of the macula (a specialized area of the retina that gives us the sharpest vision). With time, loss of side vision develops as a ring of blindness develops around this central area. Clinically this often results in tunnel vision as the visual field is narrowed. This is a progressive disorder but vision is highly variable with some individuals retaining good vision and others having extremely poor vision.
There are no general systemic defects associated with choroideremia, but there are a few reports of individuals with deafness and obesity.
Genetics
Inheritance
This is an X-chromosome recessive disorder resulting from a mutation in a gene on the X-chromosome. To inherit choroideremia, a male has to receive a mutation from his mother (fathers do not pass their single X-chromosome to their sons). Females who are carriers of the mutated gene usually have no symptoms, since they have one normal copy of the gene. However, there have been a few reports of affected females.
Pedigree
X-linked recessive, father affected
X-linked disorders are caused by a mutation on the X chromosome and both sexes can pass this to their children. If the mutation is in a recessive gene and carried by the father, he has the disease since his only X chromosome is mutant and he has no normal X to blunt the effects of the abnormal gene. His sons only receive his Y chromosome and thus are all normal. However, all his daughters receive his one and only X chromosome and will be healthy 'carriers'. Thus such males will have no affected children but half their grandsons from those daughters will have the same disease as he does.
X-linked disorders are caused by a mutation on the X chromosome and both sexes can pass this to their children. If the mutation is in a recessive gene and carried by the father, he has the disease since his only X chromosome is mutant and he has no normal X to blunt the effects of the abnormal gene. His sons only receive his Y chromosome and thus are all normal. However, all his daughters receive his one and only X chromosome and will be healthy 'carriers'. Thus such males will have no affected children but half their grandsons from those daughters will have the same disease as he does.
X-linked recessive, carrier mother
X-linked disorders are caused by a mutation on the X chromosome and both sexes can pass this to their children. If the mutation is in a recessive gene and carried by the mother, she usually does not have the disease since the normal X chromosome without the mutation neutralizes the mutation in the abnormal X chromosome. However, half her sons will inherit the mutation-containing X chromosome and therefore have the X-linked disease. Half the daughters will inherit the mutation-bearing X chromosome and are usuallly healthy 'carriers'.
X-linked disorders are caused by a mutation on the X chromosome and both sexes can pass this to their children. If the mutation is in a recessive gene and carried by the mother, she usually does not have the disease since the normal X chromosome without the mutation neutralizes the mutation in the abnormal X chromosome. However, half her sons will inherit the mutation-containing X chromosome and therefore have the X-linked disease. Half the daughters will inherit the mutation-bearing X chromosome and are usuallly healthy 'carriers'.
Diagnosis and Prognosis
Choroideremia is usually diagnosed by an ophthalmologist after a dilated eye exam based upon the appearance of the inside of the eye. In cases where the diagnosis is unclear, a genetic analysis can be performed. A special test called electroretinography (ERG) can also be done to confirm the diagnosis. Vision is highly variable and usually stable, but can in some individuals get worse with time.
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