Cone-rod dystrophy Health Article

Definition

Cone-rod dystrophy (CRD) is a progressive retinal degenerative disease that causes deterioration of the cones and rods in the retina and frequently leads to blindness. Cone-rod dystrophy is also accompanied by amelogenesis imperfecta, an abnormality affecting the teeth.

Description

Cone-rod dystrophy is characterized by all of the following elements: skin pigmentation abnormality; involuntary, rhythmic movements of the eyes (nystagmus); degeneration of vision (optic atrophy); and sensitivity to light (photophobia).

Cone-rod dystrophy can be inherited as either an autosomal dominant or autosomal recessive trait. In its most common form, however, it is usually inherited as an autosomal recessive trait, which means that both parents have one copy of the cone-rod dystrophy gene but do not have the disease. Autosomal recessive cone-rod dystrophy (arCRD) is a genetically heterogeneous disease with changes (mutations) in the ABCR gene. These mutations cause an abnormality in rod outer segment function that ultimately leads to dysfunction or death of the photoreceptor cells in the retina.

Genetic profile

The CRX gene has been shown to contain mutations that cause an autosomal dominant form of cone-rod dystrophy. This means that only one parent has to pass on the gene mutation in order for the child to be affected with the disease. This genetic form of CRD is clinically known as CORD2, or cone-rod dystrophy 2. Mutations in the CRX gene interfere in the development process of embryonic photoreceptor cells during the early stages of life. The result is abnormal photoreceptor cells with reduced function.

Demographics

Inherited retinal degeneration dystrophies have an incidence of approximately one in 4,000 people. Conerod dystrophy is an uncommon entity. The prevalence is estimated to be in the range of one in 10,000 to one in 100,000.

Signs and symptoms

The earliest symptom of CRD is loss of night vision that usually begins after the age of 20. The vision loss is progressive and unrelenting. Over the next decade, loss of all vision begins and by age 50, most people with cone-rod dystrophy have gone completely blind.

Cone-rod dystrophy is occasionally accompanied by amelogenesis imperfecta, which is characterized by abnormally shaped teeth and abnormalities in the tooth enamel.