Inherited Disorders of Copper Transport

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1. ATP7A gene therapy in murine models of Menkes disease. Menkes disease is a lethal infantile neurodegenerative disorder of copper metabolism caused by mutations in a P-type ATPase, ATP7A. Currently available treatment is ineffective in a majority of affected individuals and mortality is high. The mottled-brindled (mo-br) mouse recapitulates the Menkes phenotype, including abnormal copper transport to the brain owing to mutation in the murine homolog, Atp7a, and dies by 14 days of age. We documented that mo-br mice on C57BL/6 background were not rescued by peripheral copper administration, and used this model to evaluate brain-directed therapies. Neonatal mo-br mice received lateral ventricle injections of either adeno-associated virus serotype 5 (AAV5) harboring a reduced-size human ATP7A (rsATP7A) complementary DNA (cDNA), copper chloride, or both. AAV5-rsATP7A showed selective transduction of choroid plexus epithelia and AAV5-rsATP7A plus copper combination treatment rescued mo-br mice; 86% survived to weaning (21 days), median survival increased to 43 days, 37% lived beyond 100 days, and 22% survived to the study end point (300 days). This synergistic treatment effect correlated with increased brain copper levels, enhanced activity of dopamine-beta-hydroxylase, a copper-dependent enzyme, and correction of brain pathology. These findings provide the first definitive evidence that gene therapy may have clinical utility in the treatment of Menkes disease. Further preclinical proof-of-concept investigations involving AAV serotypes with the capacity for neuronal and glial cell transduction (AAV9, AAVrh10) are under investigation. 2. Novel molecular defects associated with disordered copper metabolism. In collaboration with others, we characterized patients from five families with an unknown disorder of copper metabolism. We documented defects in in SLC33A1 that encodes a highly conserved acetylCoA transporter (AT-1), required for acetylation of multiple gangliosides and glycoproteins. The mutations were found to cause reduced or absent AT-1 expression and abnormal intracellular localization of the protein. We showed that AT-1 knockdown in HepG2 cells led to reduced ceruloplasmin secretion. The finding revealed an essential role for AT-1 in proper post-translational modification of numerous proteins, without which normal brain development is interrupted. We have also participated in the basic science and clinical delineation of MEDNIK syndrome, caused by mutations in an adaptor protein 1 subunit that affects intracellular trafficking of ATP7A and ATP7B.