by Dan Roberts
Cone-Rod Dystrophy (CRD) is an inherited progressive disease that causes deterioration of the cone and rod photoreceptor cells and often results in blindness. It can be found as an autosomal dominant trait, but it is usually acquired as autosomal recessive.Symptoms of CRD are seen as decreased visual acuity in the early stages followed by loss of peripheral vision. The disease is similar to retinitis pigmentosa in this way, but there is no loss of night vision, the rate of rod and cone degeneration is equal, patterns of visual field loss are different, and the rate of rod ERG loss is significantly lower in CRD (Birch and Anderson)
There is currently no treatment or cure for CRD, but researchers have identified two genes which may eventually provide answers. These are the CXR and ABCR genes. Mutations in the CXR gene cause interference in the development of embryonic photoreceptor cells (Cell, November 1997). Mutations in the recently-discovered ABCR gene (Allikmet et al.'97 Nat. Gen. 15:236-246) lead to lipofuscin accumulation in the retinal pigment epithelium (RPE). This buildup of fatty waste deposits in the RPE (as in Stargardt's disease) eventually starves the photoreceptor cells (Cell, July 1999). A cure may eventually come either from a process by which lipofuscin buildup can be blocked or from advances in gene replacement therapy. In the meantime, researchers have shown that people with CRD can help to slow down the progression of the disease by protecting their retinas from bright light (Weng at al. '99 Cell 98: 13-23). For more discussion on this subject, see "Stargardt's Patients Need Special Light Protection" in the MD Support Library.