Bilateral cataract in acrodermatitis enteropathica

Zinc and the Eye

Zinc, a trace element that influences cell metabolism through a variety of mechanisms, appears to play an integral role in maintaining normal ocular function. This element is present in high concentrations in ocular tissue, particularly in retina and choroid. Zinc deficiency has been shown in a number of species to result in a variety of gross, ultrastructural and electrophysiologic ocular manifestations. The physiological functions for zinc have been studied predominantly in retina and retinal pigment epithelium where zinc is believed to interact with taurine and vitamin A. modify photoreceptor plasma membranes, regulate the light-rhodopsin reaction, modulate synaptic transmission and serve as an antioxidant. Suboptimal zinc status in North America may influence the development and progression of several chronic eye diseases. Zinc supplementation trials and epidemiological studies have produced conflicting results concerning the role of zinc in age-related macular degeneration. Additional well-controlled supplementation trials are indicated to clarify the role of zinc in this disease. Future investigations must also expand our understanding of the mechanisms by which zinc regulates ocular morphology and function.

Clinical and laboratory diagnosis of acrodermatitis enteropathica

Acrodermatitis enteropathica is an inborn error of metabolism resulting in zinc malabsorption and severe zinc deficiency. From personal experience and a literature review the following conclusions were drawn: 1. Symptoms other than dermatitis, vary with age. Diarrhoea, mood changes, anorexia, and neurological disturbance were reported most frequently in infancy. Growth retardation, alopecia, weight loss and recurrent infections were prevalent in toddlers and schoolchildren. Spontaneous remission may occur at adolescence. 2. The severity of symptoms also varies. Intermittent or mild cases of the disease and those presenting with uncommon features such as ophthalmic, cerebral or hepatic involvement, are easily overlooked. In the severe cases this may result in a fatal outcome. If untreated, the overall mortality rate is 20%, being higher in males. 3. The laboratory diagnosis is hazardous. In patients, mean zinc values in serum, urine and hair were ca. 50% of normal levels. There is a 15% overlap with healthy controls; moreover, low zinc levels in serum, urine or hair are also found in other diseases. A more specific test is required. 4. In cases of doubt, in vitro or in vivo zinc absorption tests using radioisotopes (65Zn or 69mZn) may be performed. These appear not to be influenced by other conditions and show less overlap with controls. If such tests are unavailable, the clinical response to 3-30 mumol zinc/kg per day for 5 days may be awaited. This is recommended in infants or children with one or more symptoms of acrodermatitis enteropathica.

Ocular histopathology of acrodermatitis enteropathica

Acrodermatitis enteropathica is the clinical expression of congenital zinc deficiency and is now treated with supplemental zinc. This report details the ocular histopathology of a child who died before efficacious treatment was available. The findings include corneal epithelial thinning and loss of polarity, anterior corneal scarring and loss of Bowman's membrane, cataract formation, ciliary body atrophy, retinal degeneration, RPE depigmentation, and optic atrophy.

Zinc metabolism in malabsorption syndromes

Zinc deficiency may complicate many gastrointestinal malabsorptive states. Zinc deficiency may manifest itself in a myriad of ways, ranging from skin lesions to immune dysfunction. This paper reports many of the ways in which zinc deficiency may appear in malabsorption syndromes and possible mechanisms for the development of this zinc deficiency.

Zinc in the eye

Zinc has long been recognized as an essential constituent of various tissues. Many clinical conditions and dietary factors reduce the absorption or the biological availability of zinc, and lead to zinc deficiency which produces structural and functional alterations in many organ systems. The highest concentration of this trace element in the human body is measured in the eye, particularly in the pigment-containing components. The deficiency of zinc has a dramatic effect on ocular development especially when it occurs during early prenatal period. Zinc is required for the structure and activity of many ocular metalloenzymes. Although the exact mechanism of its molecular and cellular functions are largely unknown the essentiality of this element in the component of the eye, including the retina, choroid, cornea and lens, is well established; it is also well known that zinc deficiency causes functional impairments in various parts of the eye. Zinc related toxicities have been shown in human and animal eyes.

Myotonic dystrophy: a disease caused by functional zinc deficiency due to an abnormal zinc-binding ligand?

There are large amounts of zinc in muscle and zinc ions can enhance the degree of muscle contraction in response to direct stimulation while at the same time inhibiting neuromuscular transmission. The opposites of these effects would lead to myotonia and muscle weakness. There are many parallels between the non-muscular features of myotonic dystrophy and those of zinc deficiency. The particular patterns of reproductive disturbance in both males and females, the abnormalities of metabolism, the defects in gut funcion, the defects in bone and the congenital abnormalities are very similar in the two conditions. However there are important differences between simply zinc deficiency states and myotonic dystrophy which mean that the latter is unlikely to be due to the former. Instead it is proposed that the fundamental defect in myotonic dystrophy is the presence of an abnormal zinc binding ligand which fails to deliver appropriate amounts of zinc ions to the tissues. The functioning of this ligand may, however, be affected by dietary zinc, perhaps accounting for the apparent variation in the expression of the dominant myotonic dystrophy gene due to some unknown environmental factor. Some of the effects of zinc may be due to lack of the zinc ion directly, while others are probably related to defects in essential fatty acid and prostaglandin metabolism. The hypothesis can be readily tested by the employment of nutritional measures designed to counteract the defects in zinc and essential fatty acid metabolism.