Acrodermatitis Enteropathica

A rare inherited inborn error of metabolism resulting in a severe zinc deficiency and characterized by acral dermatitis, alopecia, diarrhea and growth failure.

Epidemiology

The prevalence of Acrodermatitis enteropathica (AE) is unknown. It is more common in the North-West of Tunisia.

Clinical description

AE usually presents in the first 4-10 weeks of life in infants that are not breast-fed and at around the time of weaning in breast-fed infants, as cow's milk contains more zinc-binding phytates that impede zinc absorption. AE is characterized by eczematous pink scaly plaques that can become pustular, vesiculobullous, psoriasisform or crusted. Lesions usually involve the acral, periorificial and typically the anogenital areas. Skin lesions may evolve into erosions without treatment and are susceptible to secondary staphylococcal and candidal infections. Diarrhea, generalized alopecia and Beau-Reil lines on the nails are frequent manifestations. Paronychia, conjunctivitis, blepharitis and erythematous oral mucous membranes are also sometimes observed. Other features associated with severe and chronic zinc deficiency include failure to thrive, mental slowness, photophobia, hypogeusia, anemia, poor wound healing, hypogonadism in males, and delayed puberty.

Etiology

AE is due to a mutation in the SLC39A4 gene (8q24.3) that encodes a zinc transporter protein (called the Zip4 transporter). Zip4 is needed for the transcellular absorption of zinc into the enterocytes of the duodenum and jejunum where the ZnT-zinc transporters (that are not affected) allow for the transport of zinc into the bloodstream. Mutations in the SLC39A4 lead to zinc malapsorption. This can only be corrected by a high dietary intake of zinc that allows for a small fraction of zinc to be absorbed paracellularly, without the aid of Zip4.

Diagnostic methods

Diagnosis is based on clinical findings (diarrhea and acral dermatitis) as well as laboratory testing. Patients have low plasma zinc concentrations and low levels of serum alkaline phosphatase. Molecular genetic testing can identify a mutation in the SLC39A4 gene, confirming diagnosis of AE.

Differential diagnosis

Differential diagnoses include impetigo contagiosa, candidiasis, psoriasis, and other pathogen-related skin diseases. Sickle cell disease and related diseases, non-genetic or acquired causes of zinc deficiency such as glucagonoma (see these terms), chronic liver and renal diseases, nutritional deficiency, chronic inflammatory bowel diseases, AIDS, burn injuries, and excessive perspiration in hot climates should also be excluded.

Genetic counseling

AE is inherited autosomal recessively. Genetic counseling is recommended to identify other affected family members before the onset of symptoms.

Management and treatment

There is no cure for AE. In the majority of cases, zinc supplementation therapy results in the disappearance of AE symptoms, but this treatment is life-long and relapses can occur. Initial dosages of 5-10 mg/kg/day of elemental zinc, followed by maintenance doses of 1-2 mg/kg/day are recommended and are taken orally. Zinc sulphate is the best tolerated preparation, in most cases, but it can also be administered as acetate, gluconate and amino acid chelates. Zinc and copper levels should be monitored regularly. Dosages need to be increased during periods of growth, such as adolescence and during pregnancy, when relapses can occur.

Prognosis

With adherence to life-long zinc substitution therapy, the prognosis is good. Only when infants are left untreated can the disease be fatal.