ABSTRACT
Progressive degenerations of the retina and the choroid are the common feature of chorioretinal disorders. The electrophysiologic findings of this group of disorders are not diagnostic but may be helpful to rule out other retinal dystrophies as well as to assess retinal function. Chorioretinal degenerations involving primarily the macula such as central areolar choroidal dystrophy are discussed in Chapter 10. The outline of this chapter is:
Choroideremia Gyrate atrophy Hereditary choroidal atrophy Helicoid peripapillary chorioretinal degeneration Pigmented paravenous retinochoroidal atrophy (PPRCA)
CHOROIDEREMIA
Choroideremia is a X-linked recessive dystrophy characterized by progressive early-onset atrophy of the retina and
choroid. The disorder was first described in the 19th century and is now known to be produced by mutations of the gene encoding component A of Rab geranylgeranyl transferase called Rab escort protein-1 (REP-1) (1). The enzyme attaches geranylgeranyl lipid groups to selected intracellular proteins called Rab proteins. Rab proteins control cellular secretory and endocytic pathways. Choroideremia is a disease confined to the retina, because there are two Rab escort proteins, REP-1 and REP-2. In choroideremia patients, REP-1 is defective but REP-2 is functional. Retinal cells need both REP-1 and REP-2 to function properly but most cells elsewhere function adequately with only REP-2. Several different mutations of the REP-1 gene are found in association with choroideremia, and variable symptoms and features are frequently encountered. A recent histologic, immunocytochemistry study suggests rod photoreceptors as a primary site of pathology in choroideremia (2).
