Abetalipoproteinemia is an autosomal recessive disorder in which the apolipoprotein B is not synthesized, leading to fat malabsorption, fat-soluble vitamin deficiencies, and retinal and spinocerebellar degeneration. Red blood cells show acanthocytosis. Therapy with vitamins A and E is needed to prevent or ameliorate the retinal degeneration. Testing for vitamin A levels is useful diagnostically in these and other retinopathies associated with vitamin A deficiency states.
The most common form of vitamin A deficiency retinopathy occurs in patients who have undergone gastric bypass surgery for obesity or small bowel resection for Crohn disease. These patients have malabsorption problems and may develop a blind loop syndrome, where an overgrowth of bacteria consumes vitamin A. The patient notes night blindness and, if the condition is untreated, eventually demonstrates loss of foveal function and diffuse drusenlike spots similar to those in retinitis punctata albescens. Prior to the development of retinal degeneration, the condition is fully reversible through vitamin A therapy.