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Inborn errors of amino acid metabolism are inherited defects of enzymes that result in important disturbance in amino acid biology.1 Most of them are autosomal recessive disorders. Amino acids are the molecular units that make up proteins, and all proteins are various combinations of 20 specific naturally occurring amino acids.

Diseases of amino acid metabolism may lead to multiorgan disorders with signs and symptoms of mental retardation and dysfunction in numerous additional organs, including skin and hair.2 With more sophisticated diagnostic techniques, metabolic diseases have gained increasing importance, and numerous rare entities have been identified, including hyperphenylalaninemias, hypertyrosinemias, disorders of histidine metabolism, disorders of proline and hydroxyproline metabolism, hyperornithinemias, dysfunctions of urea cycle enzymes, disorders of lysine metabolism, disorders of branched-chain amino acid and keto acid metabolism, disorders of transsulfuration with homocystinuria and homocystinemia, sarcosinemia, and nonketotic hyperglycinemia.3

Several diseases have important cutaneous manifestations that might be a clue to diagnosis (Table 131-1). An example of such a key manifestation representing errors of amino acid metabolism is acrodermatitis acidemica. These patients have characteristic cutaneous lesions that are similar to those in acrodermatitis enteropathica (see Chapter 130). Psoriasiform dermatitis on the trunk and extremities may occur together with diffuse alopecia and brittle hair.4 In general, acral dermatitis with perioral erythema and desquamation is associated with poor feeding, lethargy, hypotonia, vomiting, and dehydration. Patients often have progressive neurologic symptoms. Patients with branched-chain aminoacidopathies may have methylmalonic acidemia, propionic acidemia, glutaric acidemia, biotinidase deficiency, multiple carboxylase deficiency, or maple syrup urine disease, all of which are sometimes accompanied by cutaneous problems.

Table 131-1 Inherited Disorders of Amino Acid and Organic Acid Metabolism with Skin Manifestations

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