A copper treatable Menkes disease mutation associated with defective trafficking of a functional Menkes copper ATPase

Copper dependency in humans is most dramatically illustrated in Menkes disease, an X linked recessive copper deficiency disorder that is generally lethal in early childhood. 1, 2 Menkes disease is caused by mutations in a transmembrane copper transporting P type ATPase, MNK (or ATP7A), which is expressed in virtually all non-hepatic tissues. 3- 5 Studies using cultured cells suggest that MNK is located in the trans-Golgi network (TGN), where it transports copper to copper dependent enzymes synthesised within secretory compartments. 6- 8 In addition to this biosynthetic role, MNK functions in the efflux of excess copper from cells via a process of copper stimulated trafficking to the plasma membrane. 6, 9 Copper export via MNK from intestinal enterocytes is essential for supplying the blood with dietary copper. Cell lysates (20 [micro]g) were fractionated by non-reducing 7.5% SDS-PAGE and tyrosinase activity was colorimetrically determined by incubating gels for 15 minutes at 37°C in 10 mmol/l phosphate buffer (pH 6.8) containing 1.5 mmol/l L-3,4-dihydroxyphenylalanine and 4 mmol/l 3-methyl-2-benzothiazolinone hydrazone (Sigma).\n Genotypic studies have indicated that a correlation exists between the clinical severity of Menkes disease and the type of mutation. 18, 29- 31 Null mutations involving deletions and early frameshifts have been identified only in severely affected patients with classical Menkes disease, whereas milder forms of Menkes disease have been associated exclusively with splicing mutations or missense mutations where the possibility exists for the expression of MNK protein with residual copper transport function. 30 As with the correlation between genotype and disease severity, it is highly probable that the response to copper therapy is also closely correlated with genotype, as is the case with treatment response for other inherited metabolic disorders.