Manganese Neurotoxicity and Familial Disorders of Manganese Transport

Manganese is the 12th most common element in the Earth's crust and is an essential industrial component. Biologically, this metal plays an important role as a constituent of numerous enzymes. While manganese is required for normal biochemical and physiological processes, manganese excess can lead to significant toxicity, particularly to the central nervous system. Over the past 25 years, three inherited disorders of manganese transport have been described, leading to a model of how this essential metal is absorbed, distributed to tissues, and eliminated. The first part of this review describes the clinical features and cellular mechanisms of manganese toxicity due to occupational and environmental exposure. The remainder of the review discusses the familial disorder associated with hypomagnesemia, SLC39A8 deficiency, and the two genetic diseases resulting in hypermanganesemia, SLC30A10 deficiency and SLC39A14 deficiency. These latter two disorders are treatable, and the early recognition and institution of chelation therapy and iron supplementation can improve neurological disability. Ongoing research regarding the tissue-specific role of each transporter and their regulatory interplay, the varied mechanisms of manganese toxicity, and its treatment are also described.