The Menkes and Wilson disease genes counteract in copper toxicosis in Labrador retrievers: a new canine model for copper-metabolism disorders

Abstract

The deleterious effects of a disrupted copper metabolism are illustrated by hereditary diseases caused by mutations in the genes coding for the copper transporters ATP7A and ATP7B. Menkes disease, involving ATP7A, is a fatal neurodegenerative disorder of copper deficiency. Mutations in ATP7B lead to Wilson disease, which is characterized by a predominantly hepatic copper accumulation. The low incidence and the phenotypic variability of human copper toxicosis hamper identification of causal genes or modifier genes involved in the disease pathogenesis. The Labrador retriever was recently characterized as a new canine model for copper toxicosis. Purebred dogs have reduced genetic variability, which facilitates identification of genes involved in complex heritable traits that might influence phenotype in both humans and dogs. We performed a genome-wide association study in 235 Labrador retrievers and identified two chromosome regions containing ATP7A and ATP7B that were associated with variation in hepatic copper levels. DNA sequence analysis identified missense mutations in each gene. The amino acid substitution ATP7B:p.Arg1453Gln was associated with copper accumulation, whereas the amino acid substitution ATP7A:p.Thr327Ile partly protected against copper accumulation. Confocal microscopy indicated that aberrant copper metabolism upon expression of the ATP7B variant occurred because of mis-localization of the protein in the endoplasmic reticulum. Dermal fibroblasts derived from ATP7A:p.Thr327Ile dogs showed copper accumulation and delayed excretion. We identified the Labrador retriever as the first natural, non-rodent model for ATP7B-associated copper toxicosis. Attenuation of copper accumulation by the ATP7A mutation sheds an interesting light on the interplay of copper transporters in body copper homeostasis and warrants a thorough investigation of ATP7A as a modifier gene in copper-metabolism disorders. The identification of two new functional variants in ATP7A and ATP7B contributes to the biological understanding of protein function, with relevance for future development of therapy.

Sensitivity and Specificity of PlasmaALT,ALP, and Bile Acids for Hepatitis in Labrador Retrievers

“…Copper‐associated hepatitis is one of the most common forms of primary hepatitis in dogs as shown by a study conducted in 101 purebred and crossbred dogs in the Netherlands, of which up to 36% of the CH and 24% of the AH cases were copper‐associated. 1 The Labrador retriever is a dog breed known to be affected with hereditary copper‐associated hepatitis, influenced by environmental factors such as dietary copper intake . In the current study, increased hepatic copper concentrations were present in Labrador retrievers with different histologic diagnosis, including histologically normal liver, but concentrations were highest in dogs with AH.…”

ACVIM consensus statement on the diagnosis and treatment of chronic hepatitis in dogs

“…The most common toxic injury causing CH in dogs is a consequence of hepatic copper (Cu) excess . Copper‐associated CH (CuCH) may develop in any breed, including mixed breeds, but the Bedlington Terrier (BT), Dalmatian, Labrador Retriever (LR), Doberman Pinscher, and West Highland White Terrier are predisposed.…”

“…Recently, a candidate gene ABCA12 has been implicated independent of the COMMD1 deletion . Cu‐mediated liver injury in LR may be influenced by mutations in ATP7B gene, which predispose to Cu accumulation, and mutations in ATP7A gene, the intestinal Cu transporter, which protects against Cu accumulation . Although genetic testing for these mutations is commercially available, the predictive and diagnostic utility of such testing currently is unknown.…”

Phenotypic convergence of Menkes and Wilson disease

“…4 ATP7A variants as modifiers have been studied in Wilson disease based on a recent canine model carrying mutations in either ATP7A or ATP7B . 5 The 2 proteins share sequence homology for residues involved in copper translocation, regardless of their directionally different trafficking. A 38 amino acid segment within the third transmembrane domain is implicated in the trans-Golgi retention of ATP7A.…”