Mutation analysis of copper transporter genes in patients with ethylmalonic encephalopathy, mitochondriopathies and copper deficiency phenotypes

Abstract

The trace metal copper is an essential cofactor for a number of biological processes, including mitochondrial oxidative phosphorylation, free-radical eradication, neurotransmitter synthesis and maturation, and iron metabolism. Consequently, copper transport at the cell surface and the delivery of copper to intracellular proteins are critical events in normal cellular homeostasis. Four genes have been reported to influence the cellular uptake and the delivery of copper to specific cell compartments and proteins. These include hCTR1, which regulates cellular copper uptake; HAH1, which mediates the transfer of copper to the Menkes and Wilson disease transporters; CCS, which is related to the transfer of copper to superoxide dismutase; and hCOX17, which directs trafficking of copper to mitochondrial cytochrome-c oxidase. At present, no genetic disorders have been associated with defects in these four copper transporter genes. In this study, we test the possibility that defective copper uptake or intracellular translocation represents the basic defect in three categories of candidate phenotypes among 22 patients: ethylmalonic encephalopathy; mitochondriopathies of unknown aetiology; and neurodevelopmental abnormalities with clinical and chemical evidence of copper deficiency. Mutation analyses of the copper uptake protein, hCTR1, and the three copper chaperones were performed by direct sequencing of the whole coding regions. No causative mutations were identified for the four copper transporter genes in 22 patients. A heterozygous polymorphism (847G>A) for CCS was detected in 7 patients. For the distinct disease entity ethylmalonic encephalopathy, we additionally show normal mRNA levels for each of the four genes. The negative results notwithstanding, we encourage ongoing study of additional patients with candidate phenotypes. Further, our results are consistent with the notion that other unknown copper-related transporters could be involved in diseases.